Int J Prosth November December 1999 Volume 12 Issue 5

Guest Editorial

Prosthodontics—Where to Now?

D

ental schools are being chalienged on many fronts and need measured discussion for planning a different set of priorities in dental education. The 1995 Instilule of Medicine report' comprehensively addresses these issues and has inspired comment and ¡ustificalion for rapid change.

The basis for the challenges faced by dental schools is threefold, involving changing community oral healthcare needs, the need to introduce appropriate learning methods for students who are more demanding and computer sltilled, and finally, a revision ot funding priorities in universities. The iast tactor has left dentai schools vulnerable; their high costs and traditional emphasis on face-to-face teaching must be balanced against the expense of quality research. Oral healthcare is becoming more demanding with the "graying" of communities and with the increasing complexity of care required, especially for elderly, intellectually and physically disabled, and medically compromised patients. The unmet need tor even primary oral care in the lower socioeconomic groups is a major community concern.

Dental schools are addressing educational resource issues,^"^ together with the need for: fV clear accountability to governments and universities as well as the communities they serve; Í2) developing alternative funding sources: (3> enhancing research output and competitiveness in gaining research grants; I4I developing strategic educational links with medicine and other health science disciplines' ': (51 broadening the educational experience of students; and ¡61 engendering an enthusiasm tor litelong learning through continuing professional education.

These are not impossible challenges. On the contrary, the need for dental schools to rechart educational, organisational, and funding directions and priorities is timely and there is a degree of excitement about the possibilities. Educational change is facilitated by our students, who are impressive in their capabilities and willingness to take on tasks independently as in smali-group problem-based learning (PBLt.--'-^ Unlike their predecessors they are computer skilled, which is an appropriate foundation for both clinical skills development and self-directed leaming.

Undergraduate Prosthodonlics The undergraduate curriculum in prcsthodontics should be based on community needs, which vary significantly within cities, between cities and rural communities, between states, and between countries. Prosthodontic programs need to reflect each country's overall priorities and be sufficiently flexible to meet changing needs.

Undergraduate programs cannot be expected to develop competence in all areas of prosthodontics. Programs should provide background knowledge in key areas and more indepth knowledge and clinical skills in the areas that are the focus of community need. Whatever the balance, new graduates will be inexperienced and will have limited procedural skills development, although their knowledge base is probably greater than at any other time in their career Clinicians in practice are often concerned at the apparent lack of skills and clinical experience ot their new assistants, but unfortunately fail to remember their own level ot expertise at the same stage.

There is a need for ongoing vocational training (VTl for all new graduates. Many European countries have introduced vocational training programs (VTP) to accommodate their own community needs, and such a program has been under consideration in Australia.

A VTP enhances clinical confidence at a time when new graduates are most in need of further skills development. It provides an opportunity to gain experience through a series of rotations in urban and rural general practice, public health clinics, and major public hospitals. These experiences are fundamental for many new graduates in deciding their preferred career path and have the added benefit of enhancing procedural skills before they enter practice Prosthodontics would benefit greatly trom VTP programs as currently all aspects of this tield sutfer trom insufficient clinical experience in the undergraduate curriculum. The pressures of commercial marketing are another concern that should be addressed'' through VTP programs as many dentai graduates lack the knowledge or confidence to question new developments in materials and techniques.

The general guidelines for undergraduate prosthodontics have been defined'-"; it remains for each dental school to determine the appropriate instruction time to be allocated to didactic, preclinical, and clinical aspects of the areas of prosthodontics most relevant to their community needs. The development of procedural skills requires an interdisciplinary focus that emphasizes total oral healthcare and is based on comprehensive treatment planning. Such an approach will maximize the educational experience and optimize oral health outcomes for each patient. Undergraduate prosthodontics includes three main clinical requirements, which may vary in relative proportion in individual schools and require a change in emphasis from past programs:

Prosthodontic Training Removable prostiiodonEics has been the cornerstone of dental education in terms of curriculum time devoted to clinical and technical procedures. Technical requirements were often overwhelming and of questionable relevance to dental practice.

The need for a change in emphasis from technology to biology^ is now recognized. This may be facilitated by vertical integration of basic and biologic sciences with clinical sciences, small-group self-directed learning, and an emphasis on comprehensive oral care. Each is crucial for a contemporar>' curriculum, and these changes are already occurring in some dental schools,=••'•8 The decisions surrounding the revision of prosthodontic education have been difticult,'" and this issue bears further scrutiny.

Volume t2. Number 5,1999

1. Prirtijt denture prosttiodontics remains a simple, inexpensive alternative to implant restoration.

381

The Interrationsl lourrrsl of Prosthodoniics

Interdisciplinary planning linking primary oral care, tooth conservation, and periodontics wilh partial proslhodont íes establishes a common goal that benefits patient care.

Partial denture prosthodonlics should be introduced al the beginning of the clinical proslhodontics program.

2. Fixed and implant prosthodontics should be recognized as a core subject for undergraduate prosthodontics. Implant treatment is best introduced as a clinical simulation block in ñxed prosthodontics. It is Ideally suited for small-group PBL projects. The iniiial clinical experience may be shared by a group of students who participate in the development oía treatment plan as thefirst part of a vertical course structure allowing progressive learning and skills development.

3. Gerodontics and oral health management ot the older adult is an expanding community need. In the process of developing a knowledge base in the anatomic, histoiogic, and behavioral changes in gerodontics there is a need to integrate restorative and periodontai care with tooth loss.

The psychology of tooth loss and the problems of clinical management of complete denture patients''' logically lead to implant-supported overdenture treatment for edentulism. A clinical overdenture program is best included in the final undergraduate year, when students have more advanced clinical skills.

Skills Development and Dentolegal Responsibility Fundamental knowledge, with an emphasis on integrated diagnosis and treatment planning, is the essential requirement ofthe undergraduate program; skills development in the more demanding areas of fixed and implant prosthodontics falls outside the responsibility ofthe undergraduate program. A 1-year VTP will help to tocus the new graduate's attention on many important aspects of clinical practice, but can only be expected to develop clinical skills to a limited extent. Enhancing the more clinically and technically demanding aspects of prosthodontics requires further training, which could be offered as: (1¡ an optional second year of VT In which two or three clinical options are elected to develop knowledge and clinical skills in areas of special interest (as the second optional year ot VT now offered in the United Kingdom); or (2} postgraduate certificate or diploma programs in advanced general practice or specific disciplines, which may be offered as didactic blocks that allow the completion of clinical components in practice.

Registration authorities could be proactive in conjunction with dental schools by requiring additional training and clinical skills to ensure competence before allowing the more complex aspects of prosthodontics—especially fixed and implant prosthodontics—to be offered in practice. It is disturbing to acknowledge that the highest litigation area in dentistry has for some time involved crown-and-bridge prosthodontics and now includes implant prosthodontics (Phillips D, Personal Communication), and it is time to acknowledge that there is a need for further training and skills development as a legal requirement before complex care is offered in practice.

Graduate Prosthodontics There are now 3-year full-time clinical masters degree programs leading to specialization. Prosthodontic programs are ideally 60% to 70% clinical academic coursework and 30% to 40% research. This combination ot coursework and research is a powerful mechanism for developing advanced clinical skills in assessment, treatment planning, prosthodontic care, and critical self-appraisal.

The Inieinalional journal of Prosthodonlics 382

Links between graduate and undergraduate programs ^^ advantageous and may be developed by: iV gradúale .> dents providing clinical supervision in undergraduate ics; and (2> establishing treatment teams composed of gra uate students and senior and junior undergraduates for sharing diagnosis, treatment planning, and différent ;.T"'"^* ° integrated patient care. A treatment team approi ' '^"^ strategy !o integrate developing student expertise in a .. .'Maboratrve structure, bringing undergraduates into partnership with graduate students. Sharing patient care is an effective mechanism to broaden clinical experience.

In relation to dentolegal responsibility for specialist prosthodontic practice, registering authorities should, as is currently the case, consider the level of clinical skills in prosthodontics on the basis of the training program undertaken by each applicant. In their accreditation of prosthodontic programs, dental councils will in the future consider international benchmarking for ensuring acceptable levels of clinical training. It is envisaged that the sharing of didactic coursework units through the internet will facilitate international collaboration and benchmarking. iven Klineberg, AM, RFD, BSc, MDS, PhD IjP Associate Editor Professor of Prosthodontics University of Sydney, Australia

References 1. Field Mj. Dental Education at the Crossroads. Washington, DC: National Academy Press, 1995.

2. Howeli TH, Matlin K. Damn the torpedoes—Innovations for the future: The new curriculum at the Harvard School of Dental Medicine.! Dent Educ 1995;59:893-898.

3. Robertson PB. Diversify and critical forces in dental education. J Dent Educ 1 997;61:412-11 6.

4. Fincham AG, Baehner R, Chai y, Crowe DL, Fincham C, iskander M, et al. Problem-based learning at the University of SouthernCalifornraSchoolof Dentistry. I Dent Educ 1997;61: 417^25.

5. Valachovic RW. Making science clinically relevant, j Dent Educ 1 997;61:434-436.

6. General Dental Council. The First Five Years—The Undergraduate Dental Curriculum. GDC, 1997.

7. Creene JC. Science and the shitting paradigm in dental education. ) Dent Educ 1997;6i:407—111.

8. Wetherell J, Mullins G, Winning T Townsend G. First year responses to a new problem-based curriculum in dentistry.

Aust Dent | 1 996;41:351-354.

9. Baum B). Science education and dentistry: Improving the connection.] Dent Educ 1997;61:405-406.

10. Klineberg 1. Dentistry—Some thoughts for the tuture [guest editorial!. I Dent Res 1992;71:1,944-1,945.

11. Simonsen RJ. Dentistry today: Putting profit betöre patients.

DentAbstr 1998;43:256-258.

12. Fisher RL, Ryan !E, Nimmo A. American Association of Dental Schools—Curriculum guidelines: For removable prosthodontics; for fixed prosthodontics; In implant dentistry for general practice residency and advanced education in gênerai dentistry programs. J Dent Educ 1993;57:45-Se. 13. Ettinger RL. Implications for geriatric concepts for the prosthodontic curriculum. ! Dent Educ !992;56:690-683 14. Fisk 1, Davis DM, Frances C, Gelbier S. The emotional effects of tooth loss in edentulous people. Br Dent! 1998;! 84:90-93

Volume 12, Number 5,1999

Implant-Supported Removable Overdentures in the Edentulous Maxilla: Clinical and Technical Aspects

i^kola Ursula Zitzmann, Dr, DMD' Carlo Paolo Marinello, DMD, PhD, MS''

Purpose: The aim of this article is to describe the indication criteria and the treatmcnf planning tor a maxillar\' implant-supported removable overdenture. Proslheses are designed according to the requirements of ihe bar system and the factors influencing the e>:tension of ihe prosthesis base. Materials and Methods: The decisive factors in determining whether a bar-retained overdenlurc prosthesis is indicated should be evaluated during fhe initial clinical examination and wilh the help of a reformatted computed tomographic (CTi scan that is performed wifh a radiologie template in place.

Titanium markers represent the ideal location otthe denture leeth in the diagnostic setup so that the implant position can be selected and the available space for the bar system can be assessed vertically and boriiontaliy. Results: For the overdenture prosthesis that is solely implant supported 6 to 8 implants arc placed ideally ata distance of about 10 to 14 mm from center to center. A pretabricated bar system tbat allows the clips to be inserted beKveen the implants can then be used. When the available bone restricts implant placement to adjacent tooth positions an individually milled bar tbat includes additional frictional pins and/or retentive elements needs to be planned. The prosthesis design, in particular its buccal and palatal tlange extension, is determined during setup try-in, taking into account the patient's smile line, tbeir need tor tacial support, and their pbonetic requirements. Conclusion: Tbe removable implant-supported overdenture otters flexibility in placing implants in either adjacent tooth positions or with greater distances between them depending on the available bone, as either conventional bar and clip systems or individually milled bars can be used. Adjustment of tbe buccal prostbesis tlange and the palatal prostbesis base is made to fulfill tbe patient's requirements concerning estbetics, pbonetics, comfort, and tunction. inf j Prosthodont 1999;! 2:385-390.

concept thai summarizes the crucial factors involved in deciding whether to perform a fixed or removable implant-supported maxillary prosthesis has been described previously.' The fixed implant-supported superstructure might be the patient's preference because comfort and function are assumed to be similar 'Assistsnl Professor, Department oĂ­ Fixed arid Removable to the natural dentition.- However, there are clear inProslitodanlics and TMj Disorders. University of Baiel, Switzeriand. dication criteria for the removable implant-supported ''Professor and Ciiairman. Departmem of Fixed and Removable overdenture, for example, when tacial support is Proilhodonlics and TMJ Disorders, University of Basei, needed, when a prognathic appearance has fo be Switzerland. compensated for, or when speech disruption is to be Reprint requests: Dr Nicola U, Zilzmann. Ciinic of Fixed and treated by adjusting the palatal contour tor an ideal Removabie Prostbodontics and TMI Disorders. Dental School. S ridge. Other factors such as a high smile line, which University ofBasef. Hebeklrasse 3, CH-4056 Basel. Switzerland. is trequentiy associated with a short upper lip length Fax:* 41-61-2672660.

F

or an implant-supported prosthesis in the edentulous maxilla, the screw-retained fixed partial denture design and the removable overdenfute prosthesis are the mosf common solutions. A treatment

yoiume 13, Numbers. l

385

i al Proslhodontics

Irtiplanl-SupportetJ Overdenlures in the EdentuIoLs

Zilzmanti/iVlarinallo

Fig 1 Implant positions are planned based on the Denta-Scan, wtiich sfiows ideal interimplant spaces.

and a iiigii tonus of the orofacial muscies, determine theidisplay of the maxillary incisors and tiie alveolar mucosa. For esthetic reasons a removable overdenture may be indicated for patients who display the maxillary mucosa during speech and smiiing. An overdenture prosthesis is also indicated to restore soft and hard tissue deficits in patients with severe rĂŠsorption of the aiveoiar bone. When discussing the adyised prosthetic solution with patients the computed tomograph ic (CT] scan can be used to show the existing bone defects and convince them to accept the recommended reconstruction. Alternatively, augmentation to compensate for soft and hard tissue deficiencies can be discussed with the patient.

It Is the aim ofthis article to describe the treatment planning for an implant-supported overdonture to reconstruct the edentulous maxilla. The removable overdenture reconstruction with its different bar designs is presented in detail, including the progressive clinical procedure, wbicb is closely lini<ed to the technicai steps in the dental laboratory.

represent the ideal location ofihe denture teeth in tbe diagnostic setup. In tbe reformatted transversal sections the residual bone and the available space for the bar system become assessable in the vertical and horizontai dimensions (Fig 1). If a bar-retained removable overdenture is chosen the selection of the ideal implant sites is not restricted to the areas defined by the titanium markers. Using prefabricated elements such as the Hader-type bar-clip mechanism (Lifecore BiomĂŠdical) or the Vario-Soft system (BredentI with clip dimensions of 5 and 7 mm, respectively, a minimal distanceof about lOlo 12 mm between implant centers is required. To provide sufficient space for the clip arrangement implant placement can be planned in every other tooth position (about 14 mm apart), eg, in tbe area of the central incisors, the canines, the second premolars, and, optionaliy. in tbe second molar region or the tuberosity excluding the sinus cavity (Fig 2). However, if the transversal images in the recommended areas reveal that implant placement is not feasibie because of a reduced aiveoiar bone quantity it may be necessary to select adjacent tootb positions such as the canine, first, and second premolar regions. In tbese cases an individually milled bar is planned and retention is derived from the trictional fit of the overcast implantsupported superstructure (Fig 3). Placement of additional retentive attachments (eg, Ceka, Alpba-Dent) and/or frictional pins sbould be considered. Generally

Surgical Treatment Planning Innplant position, angulation, and length are planned on the basis of the reformatted CT scan (eg, DentaScan, Philips), which is performed with a radiologie template in place.*-^ Tbe titanium markers are generally placed in every tooth/implant position and

I of Prostliodontii

386

Zilzmann / Marinello

I m plan (-Supported Overdenlures m the Edentulous Masilla

Fig 2 Ideal implant positions are marked on the moditied template.

Fig 3 bar.

the radiologie template is used as a surgical guide during implant placement and should therefore be modified as previously described.-

overdenture. Buccal orpalatal bulk in the anterior can resultfrom inadequate implant angulation or too great a distance between the 2 anterior implants (eg, canine or first premolar region) with a V-shaped alveolar ridge contour.^ In cases where there are a reduced number of implants and their distribution is restricted to the anterior region it is necessary to construct the overdenture as combined implant- and tissue-supported prosthesis.'' When only 2 implants are placed in the canine region complete palatal coverage is required to allow for optimal support on the hard palate. Even in situations with only one anterior clip or 2 matrices a cast metal reinforcement embedded in a massive denture base is recommended to prevent any base fracture,^

ProstheticTreatment Planning Fora removable overdcnture in the maxilla, implants are normally joined with a bar splint to facilitate primary stabilization, retention, and load distribution.^ When the bar-retained overdenture is designed to be solely implant-supported the placement of 6 to 8 implants Í5 recommended.''ThÍ5 number is similar to that advised for fixed implant-supported restorations (8 to 10 implants),- because prosthesis support is also derived primarily from the implants.^ However, when planning the implant number several factors have to be considered, including bone quality, prospective loads, vertical bone height (bone quantity, which influences the implant length), and patient-related factors.

The technical requirements for proper bar fabrication include a minimum intermaxillary space of about 10 mm in the vertical dimension. This distance is measured from the alveolar ridge mucosa to the ¡ncisal edge of tbe mandibular incisors or to the occlusal plane of the posterior teeth. Standard abutments IBrânemark-type) are selected to extend 1 mm above the mucosa (see below). This means that when using the shortest 3-mm standard abutment the implant shoulder must be located at a minimal vertical distance of 12 mm from the mandibular incisai edge or occlusal plane. Care must be taken that these distances can be provided posteriorly because in this region alveolar ridge résorption is normally moderate, wbile the pneumatization of the maxillary sinus may increase considerably. Single retainers such as ball attachments or magnets should only be applied if a bar splint is not feasible, ie, if it is likely to cause overcontouring of the

u,i

'•>, Number 5,1999

Siiort inteimpiant dislances require an individuaily milieu

Flange

Considerations

For esthetic purposes the titanium abutment cylinders extending above the oral mucosa are covered by the denture base. The buccal and palatal flanges are extended to replace the missing soft and hard tissues adequately: •

•

387

The labial flange is extended in the vertical dimension according to the alveolar ridge form and the lip line to avoid displaying the buccal margin while smiling. In the horizontal dimension the thickness of the buccal flange is formed according to the need for soft tissue support.

The palatal extension is determined by phonetic considerations. An adequate contour of the S ridge is formed duringthe wax trial. In the case of a reduced number of implants (< 4) the palate should alsobeusedfor prosthesis support to decrease implant loading (combined implant- and tissue-supported prosthesis). A posterior seal with maximum coverage of the denture-bearing area is applied when only 2 implants are present.''

Journal of Pros(liodon(ics

Implanl-S端pporled Cverdentuies in Liie Edentulous Maxilla

Zitzmann /Marinello

to check for accuracy of the impression and the working cast. The technician screws the copings back to the implant replica of the master cast and spiints them with resin. During the subsequent visit this stent is tried in intraorally and checked for passive fit. If any inaccuracy is observed the stent needs to be separated and rejoined with resin, and the position of tbe impiant replica must be corrected in the master cast.

If a removable denture has been planned a diagnostic period with an ideal provisional restoration is not necessary because neither soft tissue management nor adaptation of the interproximai spaces are required. However, care must be taken during setup tryin to determine the appropriate extension of the buccal and palatai flanges with respect to the individual needs (see above). The accepted arrangement of the denture teeth in the wax triai is keyed witb a silicon or piaster index. The height of the cast-on gold cylinders is selected according to the interarch space. The bar is waxed to correspond with the ideal tooth position undertheocclusai contact areas. When the incisors are placed anterior to the residual ridge the bar should also be located more anterioriy to avoid any rotation during incising.^ When implants are lacking in the posterior region a distal bar extension can be considered. The bar waxing should contact the underiying soft tissue, but provide adequate oral hygiene access mesiodistal to the goid cylinders. Thus, it is necessaryto perform the final impression after soft tissue heaiing has taken piace.

Fig 4 Preliminary cast with selected try-in abutments, prepared impression coping splint, and impression tray tor the pickup technique.

Prosthetic Treatment Sequence The reentry is usually performed 6 months after implant surgery. Since it is difficult to predict the soft tissue healing it is recommended to place inealing abutments to extend about 1 mm above the mucosa.-' When soft tissue healing has taken place the mucosal height above the implant shoulder is measured.

Standard abutments can then be easily chosen intraorally or with the help of the try-in abutments (Abutment Selection Kit, Nobel Biocare). The abutments are ideaily piaced above the mucosal ievel fo ailow sufficient access for orai hygiene underneafh the bar. However, adequate vertical space is required toestabiish the bar system and the superstructure. The impression is then tai<L'n at abutment ievel with a custom impression tray, clastomeric impression material, and intraorally spiinted impression copings.

Depending on the number of impiants and their arrangement in the edentulous arch it might be difficult to splint the copings intracrally with resin, in such cases with several implants distributed over the entire arch, a preiiminary impression at implant Ievei during reentry is preferable. This is used for abutment selection and preparing the splinted impression copings that are screwed onto the selected try-in abutments (Fig 4). The resin splints are thinly separated and piaced intraorally when the soft tissues have healed. The splints are then rejoined with acrylic resin and the finai impression is taken at abutment ieyel with the pickup technique. This method provides the greatest accuracy because the amount of resin used for intraoral splinting is minimal, as is its shrinkage; additionally, the resin bar is entirely embedded in the impression material. If the preiiminary impression at implant Ievei is not avaiiabie and impression copings could not be splinted intraorally, then the fabrication of a verification stent is necessary

Tlie Intemalional lournal of Proslliodontii

Bar Fabrication Provided that there is sufficient space between the gold cylinders, prefabricated burnout plastic patterns (eg, Hader or Vario-Soft) with paraiiei buccolingual surfaces are inciuded in the bar waxing. With minimal interimpiant distances the waxed bar is preliminarily mi端ed wilh a 2-degree taper to create paraiiei iabial and palatal walls that coincide with the path of insertion of the superstructure. After casting the bar is finaily milled and retentive attachments (eg, Ceka) and/or frictional pins are incorporated. The bar is then checked for passive fit during try-in with FitChecker (CC) and periapicai radiographs.-'*''"'^^ Superstructure Fabrication Depending on the available palatal space the superstructure can be designed with a metal backing to obviate an irregular bulge in the phonetic zone. Using a bar-ciip system matrices are luted (eg, Hader) or just placed (eg, Bredent) in ihe Cr-Co superstructure (Fig 5). For the Bredent system, clips are available in 3 different retentive strengths and can be easily exchanged

388

Volume 12,'

Zitzmann/Marinellรป

Fig 5

implant-Supported Overdentures in the Edentulous Maxilla

Co-Cr superstructure wilh soft plastic clips.

Fig 6 Galvanized framework luted into the superstructure fits the milled bar.

with a special kit. When fabricating a milled bar an overcast that fits the bar precisely is cast using the same gold alloy for both the bar and the superstructure.'- Depending on the overcast's dimensions a large amount ot gold alloy may be required. This entails adding considerably to the weight of the maxillary superstructure. Alternatively, a galvanized framework made from pure gold by electrodeposition can be fabricated. Because the 300-[jm-thick galvanized superstructure is not sufficiently stable on its own it is luted into a Cr-Co superstructure (Fig 6ยก. The denture teeth are transferred back to the superstructure and the overdenture can be processed in heatpolymerizing acrylic resin ยกFig 7). When the superstructure is deiivered oral hygiene Instructions for the area around the bar need to be given; cleaning is usualiy performed with a thick super floss underneath the bar and interproximal brushes or a periobrush in the abutment region.

Fig 7 Finai situation with the buccal flange extending above the smile line (patient with milled bar].

place or implant failure leads to a reduced implant number. In these cases overdentures are more common as this design offers the flexibility of relying on the posterior denture-bearing areas. Additionally, financial restrictions may lead to the choice of an overdenture, which is then constructed to be implant- and lissue-supported, thereby requiring fewer implants.

If an overdenture that is solely implant-supported is planned, loads similar to those for a fixed reconstruction can be expected and, therefore, a minimum of 6 implants should be used.^'^-'^ Provided that 6 to 8 implants can be placed, the prosthesis support is derived from the implants so that no soft tissue support is needed. The extension of the buccai and palatal flange is determined during setup try-in to take into account the smile line, the need for facial support, and phonetic requirements. If the removable overdenture prosthesis can be ideally fabricated with a horseshoe-shaped design, a similar degree of comfort lo that expected with a fixed reconstruction may be achieved.

Discussion Compared to fixed screw-retained implant prostheses, in which implants should be meticulously placed in the intended tooth position, the removable overdenture prosthesis offers greater latitude with respect to implant position and angulation. For a barretained overdenture implants are best placed with an interimplant distance that allows an adequate clip arrangement; otherwise a milled bar is advised.

The success of overdenture treatment in the resorbed edentulous maxilla has recently been reviewed.'^ It was found that implant and prosthesis success rates are similar to those of fixed implant prostheses when treatments are matched for bone quantity and quality, allowing a similar number of implants with similar iengths to be placed.''' However, with severe bone loss fewer implants are possible in thefirst

Numbers,1999

389

The tnternatjonal loumal ot Prosthodonlics

Iniplanl-Sjpported Overdeiilures in tlie Edentulous

Zit^rrann/Marineilo

Acknowledgments

7.

8.

The authors wish to thank Mrs Ana Suter, Cerana Laijoratory, Zurich Gidttbmgg, ana Mr Alwin Schönen berger, Zurich Clattbrugg, for the technical work they performed with great patience and enthusiasm.

9.

References 10.

1.

Zitzmann NtJ, Marinello CP. Treatment plan for restoring the edentulous maxilla w i t h implant-supported restorations: Removable overdenture versus fixed partial denture design. | Prosthet Dent 1 9 9 9 ; 8 2 : 1 8 8 - I % .

2. Zitzmann NU, Marineliü CP. Clinical and technical aspects of irrplant-supporled restorations in the edentulous maxilla: The fixed partial denture design. Int I Prosthodont ¡ 999;12:307-312.

3. Quirynen M, Naert i, van Steenberghe D, Teerlink |, Dekeyser C, TheunicrsG. Periodontai aspects of osseointegrated fixtures supporting an overdenture. J Clin Periodontoi 1991;18:719-728.

4. Beumer ] lii, iHamada M O , Lewis S. A prosthodontic overview.

Inl) Prosthodontl993;6:l26-130.

5. Davodi A, Nishimura R, Beumer | III. An implant-supported fised-removabie prosthesis with a milled tissue bar and Hadei d i p retention as a restorative option for the edentulous maxilla.

J Prosthet Dent 1997;78:2I2-217.

6. Desjardins RP. Prostiiesis design for osseointegraied implants in the edentulous maxilla. int| Oral Maxilbfat implants 1992;7:311-320.

Literature

11.

12.

13.

14.

15.

Taylor TD. Fixed Implant rehabilitation for iheedentulous maxilla. Int 1 Oral Maxillofac Implants 1991,-6:329-337. ^ Langer V, Langer A. Root-retained overdL-ntJres. Part -— Biomechanicai and clinical aspects. | Prosthel rifnt I991;6b: ;84-789.

Lewis S, Sharma A, Nishimuta R. Treatment of cduniulous maxillae with osseointûgrated implants. I Prosthet Dcni 1992;68: 503-.5O8.

Lothigius E, Smedbcrgli, De Bucií V. Nilner K. A new design for a hybrid prostiiesis supported by osseointegrated implants: 1.

Technical aspects. Int | Oral Maxiilofac Implants 1991;6:80.-e6.

SmedbergH, Lothigius E, Nilner K, De Bucit V. A new design for a hybrid prosthesis supported by osseointegrated implants: 2.

Preliminary clinical aspects. Inl | Orai Maxillofac Implants 1991;6:154-159.

Finley | M . Restoring the edentuious maxilla using an impiantsupported, ma tr in-ass i s ted secondary casting. | Prosthodont 1998,7:35-39.

Char MFW-Y, Närhi TO, de Baat C, Kalk W. Treatment of the atrophie edentulous maxilla with i m pi ant-supported overdentures: A review of the literature, int | Prosthodont 1998;11:7.-l S. lemtT, Lekholm U. Implant treatment in edentulous maxillae: A 5-year follow-up report on patients with different degrees of jaw résorption. Int | Oral Maxillofac Implants 1995:10:303-311.

Krämer A. Weber H, Benzing LJ. Implant and prosthetic treatment of the edentulous maxilla using a bar-supported prosthesis. Int J Oral Maxiilofac Implants 1992;7:251-255.

Abstracis-

A clinical évaluation of 76 implant-supported superstructures in the composite grafted tnaxilla.

This study reports damage to implant-supported superstructures in 76 patients with 37 ouerdentures, 26 fixed partial dentures, and 13 fixed complete prostheses. Atter a mean of 22 months in function damage was found in 4 7 % of the cases. Atter 40 months ttie rate of d a m ages had increased to 7 0 % , mairily because of the fact that at that point 100% of the overdentures had damage, whereas there was no turttier increase in damage in the fixed prostheses.

A remarkable finding was that the damage rate was muoh greater for the tixed complete than fixed partial prostheses.

Kaptein MLA, De Putter C, De Lange GL, B\\\doip PA. J Oral Rehabin9S9.2B:(,'\B-623. References: 13.

Reprints: Dr M. L. A. tíaptein. Department ot Oral Maxillotacial Surgery, Prosthoäantics and Special Dental Care, Faculty ct Medicine, Unwersiry o\ Utrecht, Universiteitsweg 100, 3584C6 tjlrecht. The Netherlands—Ak

Marginal discrepancies of screw-retained and cemented metal-ceramic crowns on implant abutments. in this in uitro study 2Û ITI solid-screw dental implants (Straumann) were used, divided into 2 groups of l O s p e c i m e n s e a c h . The first group was selected to receive a cement-retained restoration, and the second group received a screw-retained restoration. Metal-oeramio crowns were fabricated for both groups according to standard laboratory protocol In the first group 5 specimens ware cemented with glass-ionomer cement and the other 5 were oemented with zino phosphate.

The rnarginal discrepancy was measured at different sites using a stereo microscope at 50 x magnification. The mean marginai discrepancy was smaller for the screw-retained crowns compared to the cemented crowns ( P < 0 . 0 0 1 ) . The discrepancy was also smaller for the crowns oemented with gtass-ionomeroement compared to those cemented with zinc phosphate ( P < 0.05)Kelth SE, Miller BH, Woody RD, HIgglntiottom FL. inlj Oral Maxillofac Impiants 1999; 14:369-378, References: 73. Reprints: Dr Scott E. Keith, 188 Longwocd Avenue, Boston. Massaciiuaetts 02115-5886—SP

The Inlernationa! lournal of Prostilodontii

390

Vclimie I ! , N - - - ' —

Prosthetic Restoration Following Maxillary Resection Without an Oroantral Defect: A Case Report

Goran Stegersjö, LDS^ Karl-Erik Kahnberg, LOS, Odont

Di''

Purpose: The aim of this article was to present tiie oral reiiabilitation of a patient witii a large, created intraorai detect after the surgicai extirpation of a pathoiogic process.

Materials and Methods: On osseo integra led oral implants, a bar was fabricated to support a partial overdenture by means of attachments. Results: The treatment was successful and the construction iias been in service for more than 5 years. Conclusion: In cases with large intraorai defects removable dentures may have ciinicai advantages over fixed partial dentures. In this patient the restoration of missing teeth, aiveoiar crest, and soft tissue was accomplished at tiie same time oral tunction was restored, and good oral iiygiene access was obtained, int ) Prosthodont 1999:12:391-394.

P

rosthetic réhabilitation of surgically created intraorai defects remaining after the extirpation of pathologic processes such as tumors is always technically difficult. Both functional and esthetic demands are very difficult to satisfy. In the past, the therapist was often iimited to extensive removable partiai dentures to restore the loss of bard as well as soft tissue. Osseo in teg rated oral implants bave made it possible to treat patients with less extensive prostheses instead of such removable dentures. Scientific data on the long-term prognosis of fixed o s seo in teg rated prostbeses^'^ are very good, and the data on overdentures^ are satisfactory. Even when bone grafts are used with implants, the survival rate is good."* New techniques today allow the use of impiant-supported prostheses to restore even large defects. Anatomic conditions may sometimes be more suited to a removable rather than a fixed impiant-supported prosthesis. An attachment-retained removable partial overdenture may be a f;reat advantage to patients wbo were previously forced to wear extensive removable partial dentures. With tbe use of intraoral impiants more

convenient prostheses can becreated.The aim ofthis article is to present the oral rehabilitation of a patient who was surgically and prostheticaliy treated for a large capiliary hemangioma" in the maxilla.

Clinical Report

A female patient was diagnosed with a large capillary hemangioma in the left part of the maxilla wben she was just 4 years oid. Her face became more asymmetrical with time, and malocciusion developed. The tumorwassurgicaiiy removed after embolization when she was 7 years old. The surgery was, however, not radical and the tumor continued to grow (Fig 1 ). A second surgery was performed 3 years iater. The teeth from the maxillary right central incisor to the left third molar were extracted and the left maxilla was partiaily resected. The resection was an infrastructure maxillectomy and resulted in the ioss of aiveoiar process but nooroantrai defect. At this time the patient received a removable partial denture (Fig 2). At the age of 17, 7 years later, a more permanent and convenient impiant-supported prosthetic treatment was planned; it was accomplished when the patient was 20.

'Head, Prosthetic Dentistry, Pubiic Oental Service, Boras, Sweden.

In the remaining part of the ieft maxilla 3 ''Professor and Chairman. Department of Oral and Ms\iihfacisi Surgery, Fgcuity of Odontology. Golebo'g University, Sweden.

Brânemari< implants (Nobel Biocare) were placed: 10Reprint requests: Dr Goran Stegersjö, Spedaiistkiiniken for Oral mm impiants in the position of the left lateral incisor and second premolar, and a 13-mm implant in the Protetik, Lilia Kyrkogatan 25, S-503 35 Boras. Sweden.

Si.VoIiime12,Ni]mber5. 1999

391

The International lojcnal of Prostfiodontii

ProsLlielit Krílor.ilinn Following Mssillary R

sjö / Kahn berg

Fig 1 Radiograph shows contihuihg growth of the tumor at the age of 10, 3 years atter first surgical treatmenL Fig 2 ¡rigtit) Occlusal view of the removable partial denture.

Fig 3a

Radiograph shows situation atter abutment connection.

Fig 3t» (rigtit) Occiusal view oí situation atter abutment connection.

studies have been based on patient assessment of the outcomeof implant therapy in terms of well being and quality of lii'e. Therefore, clinical experience, with clinical reports, is the most valuable aid when choosing between conventional and implant therapy.

The conventional way of treating this patient was to give her a removable unilateral partial denture retained by clasps. She received tbis kind of denture when she was 1 3 years old and, with continuous adjustments, it served for almost 7 years, although not without problems. The patient's complaints about the denture were that it was unstable, uncomfortable, strained the remaining teeth, and caused a lisp, and furthermore, it fractured twice. Therefore, a more permanent prosthetic treatment was planned and performed. With the technique described a comfortable treatment was carried out without any preparation of the patient's natural teeth.

In this case it would have been impossible to construct an implant-supported fixed partial denture to replace the missing teeth, alveolar crest, and soft tissue while meeting the esthetic demands of a young woman and still obtain ing oral function and allowing

position of the left canine. After a healing period of 7 months abutmeni connection was carried out with standard 7-mm abutments on all 3 implants (Fig 3).

An individually designed gold bar with vertically parallel smooth surfaces and a corresponding removable partial denture was fabricated (Fig 4). To achieve retention between the 2 parts of the prosthesis, Ipso-clips (Cendres & Métaux) were used. The prosthesis has now been in service for 5 years and the patient is very satisfied with il. During the annual checkups only a few problems have been observed.

After 2.5 years the male parts of the Ipso-clips were damaged and replaced with new ones, and after 3.5 and 5 years 2 of the gold screws connecting the bar to the abutments had to be tightened.

Discussion Fvery patient with a large surgically created defect is unique. This makes it difficult to find scientifically based data to support the choice between implants and conventional removable parlial denture therapy.

In a literature review Locker^ stated that very few

392

. 12, Numticr S, 1999

Siegersjรถ / Kahnhety

Pro^thclic Kestor.ilion Followina M.i\illjrv Rmof lion

Fig 4a

Gold bar and overdenture on model.

Fig 4b

Facial view of gold bar connected tc implants.

Fig 4c

Occlusai view ot gold bar connected to impiants

Fig 4d

Faciai view ot partiai overdenture in piace on goid bar.

Fig 4e

Occlusai view of partial overdenture in place on goid bar.

adequate oral hygiene. With the type of prosthesis described in this article there have been no problems achieving symmetry between the right and ieft sides ofthefaceorrepiacing the missing dentoalveoiar tissue. There wouid aiso have been unfavorabie, nonaxial forces on the implants'during occlusion if a fixed partiai denture had been the therapy of choice. In this type of prosthesis the removable part is the weaker part and it will be the first to break if it is overloaded, saving the implants from unnecessary complications.

There have been no problems with the patient's adaptation to the prosthesis. This corresponds weii with the results of Feine et al,^ who compared patients' preference between fixed and removabie implant-supported mandibular prostheses and found good adaptation to both types of prostheses. Finally, when removing the removabie part of the prosthesis there is full access for both a toothbrush and an interspace brush for both !he abutments and the bar.

Oral hygiene can be maintained at a high ievei.

Ipso-ciips have been used for decades in prosthetic dentistry with favorabie results as attachments connecting removable partial dentures to crowns or fixed

.Volume 12, Numbers, 1999

partial dentures in cases with only a few remaining teeth. The connection between the fixed and the removable part of the prosthesis becomes reiiabiewith the use of Ipso-clips. Among other advantages is the possibility of constructing a prosthesis that is both rigid and slender. There are also few complications associated with the ci ips, and those that occur are often

393

The Imernatioiisl lournal of Prostliodontii

Prosthetic Restoration Following Maxillary Resection

Stegersjö / Kahn berg

3. Watson RM, !emtT, Chai], HarnettJ, Heath MR, Hutlor IE, et a .

Prosthodontic treatment, patient response, and the need for maintenance of complete implant-supported overdenture^: An appraisai ofSyearsofprospectivestudy. lnt|Prasthodontl997;in:345-354.

easy to manage. The problems with the clips in this case were caused by the patient herself when she had to insert her prosthesis quickly and it was not seated in exactly the right position. Both the ball and the spring ofthe Ipso-clips were damaged and were replaced to reestablish original function.

Through careful Ireatmenl planning and the use of old as well as new knowledge and technology, the prosthetic treatment of this young woman has been successful for a follow-up period of more than 5 years.

4. Kahrbers K-£, Nystrüm E, Bartholdbsun L. Combined use of bone grafts and Bränemark fixtures in the treatment of severely resorbed maxillae. Int] Oral Maxillofac implants 19B9;4:297-3()4.

5. ShaferWG, Hine MK, Levy BM. Benign and malignant tumors of the oral cavity. In: Shafer WG, Hine MK, Levy BM (eds]. A Textbook of Oral Pathology, ed 3. Philadelphia: WB Saunders, 1974:!42-145. b. Locker D. ?atient-based assessment of the outcomes of implant therapy: A review of the literature. Int ! Prosthodont 1998;11 : 453-461.

7. Rangert BR, Sullivan RM, JemlT. Load factor control for implants ¡n the posterior partially edentulous segment. Int J Oral Masillofac Implants 1997;12:3 60-370.

8. Feine !S, de G rand mont P, Boudrias P, Brien N, LaMarcheC, Taché R, et al. Within-subject comparisons of implant-suppoiled mandibular proslheses; Choice of prosthesis.! DertRes 1994;73: 1,105-1,111.

References 1. Adell R, Eriksson B, Lekholm U, Brânemark P-l,!emtT. A long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int! Oral Maxi Ilofaclmplantç1990;5:347-3S9.

2. Lekhoim U, van Steenberghe D, Herrmann I, BolenderC, Folmer T, Cunne], etal. Osseointegrated implants in the treatment of piirtially edentulous jaws: A prospective S-year multicenter study. Int J Oral Maxillofac Implants 1994;9:627-635.

Literature Ai}str3cti-

Implant-retained overdenturesi A 5-year follow-up study of clinical aspects and patient satisfaction.

The aim ot this prospeotive randomized controlied ciinicai triai was to evaluate and compare clinical aspects and satistaction during a 5-year penod. The patients were all complete denture wearers with consistent problems. They were randomly assigned to one ct twc grcups: (tj the implantretained overdenture (IRO] group (n = 61], who received two dental implants in the mandible connected with a round bar supporting an overdenture, and a new complete maxillary denture; or (2} the conventional denture (CD] group (n - 60]. who were treated with new complete dentures.

For the IRO group two implant systems (Branemark, Nobei Biocare, and IMZ, Interpore] were equally used. Eight implants (four of each type] were lost during the follow-up period (survivai rate 93%); all patients were successtully reoperated. Before treatment there was no difference between the groups with respect to denture satistaotion as measured on a ten-point scale. One year after treatment there was a signiticant difference between the groups, with a mean ot 8.8 for the IRO group compared to 6.6 for the CD group. After 5 years there was still a significant difference.

Ttiere was no tendency to a difference between the groups regarding complaints about the maxillary denture. It was concluded that there mas a high survivai rate for the implants after 5 years, thatthere was a consistently higher satisfaction rate in the IRO group, and that implants in the mandible did not have a negative effect on the function of the maxillary denture.

Mei!erHJA, Flaghoebar GM, Vant't Hof MA, GeertmantWE, VanOort RP. Clin Oral Implants Res •\393:\0: Í38-244. References: 24. Reprints: Dr H. J. A Mei¡er. Department ot Orat-Maxiiiofaciat Surgery and tiflaxiiiofacial Prosthodontics. University Hospitai Groningen. PO Box 30 001, 9700 Rß Groningen. Tlie Netherlands—SP

Gender aesthetics in the natural dentition.

It is often suggested that there is a difference in the appearance of natural maxillary anterior teeth between men and women. This study questions that statement. Forty-six casts of natural teeth were given to eieven experts who assessed the gender of the patients. On average only 55% of the casts were correctly classified as to gender. It was concluded that dentists cannot distinguish between genders by the visual assessment of casts aione.

Hyde TP, MoCord F, Macfartane T, Smith J. Eur J Proslhodont Restorative Denl 1999:7:27-30.

References: 13. Reprtnts: Or T. Paul Hyde, Tjrnsr Dental Schoot, University Dental Hospital Of Manchester, Higher Cambndge Street, Manchester, Ml 5 6FH, UK—AW

I oí Pr05thodonlii:s

394

Í 12, Number 5, 1999

Measurement of the Margins of Partial-Coverage Tooth Preparations for CAD/CAM

Harry W. Denissen, DDS, PhD' JefM. van der Zel, PhD'' Marinus A. ) . van Waas, DDS,

Purpose: This study tested the hypothesis that a scanning laser 3-dimeiisiona[ digitizer is a precise and accurate instrument to measure chamfered and beveled margins of partialcoverage tooth preparations for computer-aided design/computer-aided manufacturing (CAD/CAM). Materials and Methods: The margins were measured by the digitizer on stone die; and calculated by triangulation into a 3-D representation, instrument precision was defined as the abilit\' to reproduce the same margin in repeated measurements and expressed as the coeĂź'icient of variation as a percentage. Instrument accuracy for chamfered and beveled margins was estimated by correlating their measurements to the measurement of the margin of a spherical calibration "phantom" with known dimensions.

Accuracy was expressed as the standard deviation. Resulfs: The precision errors for the box- and cusp-chamfered margins and cusp-beveled margins were 3,9%, 3.4%, and 2.4%. respectively. With regard to accuracy tbe sfandard deviations of the measurements of tbe box- and cusp-cbamtered margins and cusp-beveled margins were 19 pm, 21 |jm, and 24 |jm, respectively, compared to 15 pm tor the phantom. Conclusion: Measurements of chamfered and beveled margins by a scanning laser 3-D digitizer for CAD/CAM are (1) precise (error < 4%) and (2) accurate, with a standard deviation of less tban 9 (jm compared to optimal measurements of the spherical margin of the phantom.

intj Prosthodont 1999;T2:395^00.

T

he measurement of the partial-coverage tooth preparation surface is the first step in the computer production oftherestoratiotn. Partial-coverage preparafions include preparation forms that are also described as onlays, V' crowns, and f. crowns. The authors advocate chamfered and beveied preparation margins for ceramic computer-produced partialcoverage restorations.

The precise and accurate measurement of the margins is of crucial importance for the computer-aided design ICAD) and the computer-aided manufacturing

(CAM) of the partial-coverage restoration. A potentially useful method lo measure chamfered and beveled margins is the scanning laser 3-dimensional digitizer technique.' The feasibility of measuring the margins will depend on the performance of the digitizer. The assessment of instrument performance is characterized by the precision and accuracy of its measurements.- instrument precision in fhe digitizer technique is reflected by the ability to reproduce the same margins in repeated measuremenfs. The accuracy of the measuremenfs concerns the dimensional error that might occur in the measurementof the margin.

The measurement of the margin of the preparation 'Mentor, CAD/CAM Research. Department of Orai Function and Prosthetic Dentistry. Academic Center for Dentistry Amsterdam. entails a so-called optical impression with computer Tije Netherlands. surface digitization,' The scanning laser 3-D digitizer ''Teciinicai Director. Cicero Dentai Systems. technique uses a laser-stripe scanning method to mea'^Professor, Department of Orai Function and Prosthetic Dentistry, sure the 3-D geometry of the prepared tooth on the Academic Center for Dentistry Amsterdam, The Netherlands. stone die. The measurement of the dimensions of the Reprint requests: Dr H. W. Oenissen, Department of Orai Functionmargins is closely linked to the future marginal adapand Prosthetic Dentistry, Academic Center for Dentistry tation of the restoration. One way to estimate the diAmsterdam (ACTA), Louwesweg 1, ÂĄ066 EA Amsterdam, The mensional error of the measurement is to correlate Netheriands, Fax: + 31 20S188414.

S},,Volume 12, tJumberS, 1999

395

The International Journal oĂ­ Prosthodon[ics

Margins of Piirtial-Cowr.igi- Tootii PrĂŠparations for CAD/CAM

Fig l a Stone die wiih partial-coverage preparation ot a mandibular moiar. Note the ctiamtered box and buccai cusp marginai surfaces ot the preparation (c/osed arrow). The iinguai occiusal cusp has a broad, beveled surtaoe ÂĄopen arrow). The regions below the ohamtered and beveled margins were painted biack to prevent retlection of ttie laser beam.

Fig 1b Ceivical view of measured meshed surtace of the partial-coverage preparation of a maxillary molar. The wire mesh was extracted trom the data obtained from the scanning laser digitizer.

Tine chamfered margins of the boxes and the palatai cusp are indicated by dosed arrows and the beveled buccal cusp by an open arrow.

this measurement to the measurement of a calibration "phantom." The authors opted for a spherical steel phantom with a known surface.

This study tested the hypothesis that measurements of chamfered and beveied margins of partialcoverage tooth preparations by a scanning laser 3-D digitizer are precise and accurate.

Measurements with Scanning Laser 3-D Digitizer

Materials and Methods Preparation of Posterior Teeth Patients in this study had large amalgam or composite filiings that had to be replaced. Deep gingivai chamfers were prepared in the boxes and around the functional cusps (buccal aspect of mandibular teeth and lingual aspect of maxillary posterior teethi.

The functionai cusps were thus enclosed. The nonfunctional cusps (Iinguai aspect of mandibular teeth and buccal aspect of maxillary posterior teeth) were prepared with broad bevels foilowing tbe inclined occlusai plane pattern. The nonfunctional cusps were thus covered. The axial walis were prepared at the same time and the transitions from the gingival to proximai and occlusai were rounded and smoothed.

Polyether-rubber impressions (Impregum, Espe} were obtained and poured in white stone (New FujiRock, GC). Stone dies of one maxillary molar, one maxillary premolar, and one mandibular molar were used for the measurements of the surface geometry of the chamfered and beveled margins of partial-coverage preparations.

The Internarional I ou mal of Prosthodoniii

For the measurements the digitizer of the ComputerIntegrated Ceramic Reconstruction System (CICERO, Flephant Dentai Systems) was used. The surface of the shiny steei phantom was painted white to reflect the laser beam. The area of the stone die below the finish line was hand painted blaci<. Tbis was done with great exactness, using magnifying glasses to prevent errors. Consequently, the margins of the chamfered and beveled margins could be clearly extracted from the scanning data (Fig 1 ).

The phantom and stone dies were placed in a tray in a scanner-clamping device, which has a ball-andsocket scanner table that can be tilted and locked in a direction so that the patb ot insertion of the future restoration coincides approximately with the vertical Z axis of the scanner. The ciamping device of the scanner table was mounted on 2 linear translation tables that were perpendicular for X and Y axes. A ruby laser was mounted above the stone die with its beam directed |3arallel to theZaxis. The wavelength of the helium-neon laser beam was 640 nm. Tbe laser beam was expanded iiy a zoom line projector into a long, thin, straight red stripe. The focus laser had a 0.3-mm thickness. The laser beam had a fixed position but tbe scanner tabie was moved in 4 different positions toward the iaser beam.

In each position the tray was scanned 4 times.

Two charge-coupled device (CCD) cameras with retinas as laser-ligbt sensors were rigidly attached to tbe laser with their axes aligned 30 degrees from the 2 axis.

The laser beam was projected on the surface of tbe

12, Numbers, 1999

rKins of Parli-T I-Coverage Tooth Preparation; tor CAn/CAM

Fig 2a Superimposed cross seotions of 5 repeated measurements of the surfaces ot the phantom.

Fig 2b (above right) Buccal view ot a mesiodistal cross section ot a partial-cove rage preparation. Both bos-chamfered margins are indicated by arrows and the occlusal seat by s.

Fig 2c (rigtit) Mesial view of buccopalatal cross section. The beveled buccal margin is indicated by b. the seat portion by s, the lingual cusp by c. and the chamfer by CH.

phantom and stone dies. The straight projected beam was reflected by the geometry of the surfaces and the resulting illuminated spot on the phantom or slone die was captured by the CCD video cameras. The X, Y, and Z coordinates of the laser-illuminated spot on the phantom or stone die were then calculated by the computer.

This conversion of this spot into a 3-D coordinate is called triangulation. Ail laser-illuminated spots produced a 3-D representation of the surfaces of the phantom and the preparations. Tbe computer sofuvare imaged a 60-pm-thick cross section of this representation for the precision analysis ofthe measurements (Fig 2).

In a preliminary study the phantom die was measured for precision and accuracy analyses. In the definitive study the system was calibrated by means of the phantom prior to the measurements of the margins on tbe stone die.

measurements was expressed in the (relative) coefficient of variation (CV) as a percentage. The CV was defined as standard deviation (SD)/mean ofthe measurements X TOO. Accuracy. For the accuracy analysis the radius of the phantom was measured by digitizer and by light microscopy as an independent method. After surveying the white-painted phantom and indicating opposing points on its surface the radius was measured using a light microscope (Olympus BX 60), a CCD color video camera (Sony), a computer (FHewlett Packard), and Kontron software (Kontron Elektronik Imaging System KS 100, version 2.00). Five repeated microscopic measurements were done on four cross sections. Results were expressed as mean Âą SD.

Phantom Measurements

Chamfered and Beveled Margin Measurements by Digitizer

Precision, To determine the precision of the measurements of the phantom in the preliminary study up to 175,000 points were measured and analyzed on its 5urface. The measured points were tested for distribution and normality. The precision error for the phantom

Precision. Five successive measurements were made without repositioning the phantom and stone dies toward the laser beam; 60-|jm-thick cross sections ofthe 3-D representations were obtained and these five cross sections were superimposed on them. The parts

O/olume ]2, Number 5, 1999

397

Thf Intcmalionol loumal of Prosthadonlics

Denissen et al

Margins of Partial-Cove rage Toclh Preparations for CAD/CAM

Fig 3a (leñ) Enlarged marginal part of 5 superimposed mea surements ct the phantom. The thickness ot the cross seciiur is 60 |jm and the iength is 0.7 mm. The dimension of the cross seotion was defined as the distance between LI and L2 being

Fig 3b (below left)

Chamfered margin with a dimension ot 59

Fig 3c (below) Beveled margin with a dimension ot 68 [im.

section/dimension of tbe phantom cross section x SD of the measurement of the phantom.

of the superimposed cross sections extending more than 0.7 mmfrom the outiine of the preparation were enlarged on the computer screen. The centers of the uppermost and the iowermost cross sections couid tben be indicated on the screen. The distance between the centers was calcuiated and defined as the dimension of the superimposed cross sections (Fig 3).

These dimensional measurements were done for five different cross sections of the margin of the phantom and five cross sections each of the box- and cuspchamfered margins and cusp-beveied margins. The means and SDs of the dimensions of each cross section of the box- and cusp-chamfered margins and cusp-beveled margins were then calcuiated and the precision error determined.

Results Measurements by tíie Scanning Laser 3-D Digitizer The digitization trajectory for the overall scan of the tray with the dies was done in 1,600 lines in 8 views that were completed in 149.5 seconds (10.7 lines/s). Fora single die these data were 2,240 iinesinS viewscompieted in 165.5 seconds (1 .Î..S lines/s). The system was rapid and could supply approximately 100,000 surface points per minute. This is such high definition that filtering was used without any loss of information. The reliability' of the measurements increased with the density of the points on the surface. The fully automatic measurement of the stone cast, including conversion of the data, took approximately 15 minutes.

Accuracy. The SDofthe measurements of a given object determines the accuracy of the digitizer technique.^ As a parameter for correlating the accuracy of the measurements of the phantom to the chamfered and beveled margins, the dimensions of the cross sections of 5 superimposed measurements were chosen. The accuracy of margin measurement was thus calculated as dimension of the marginal cross

The In ter nations i lournal a\ Prosthodontics

Precision and Accuracy Analyses of the Phantom The number of points measured on the surface of the phantom was 75,442. The histogram showed a regular

398

Volume12, Number 5, 7993

Margins of Partial-Covtrage Tooth Preparations for CAD/CAM

Table 1

Precision Error Analyses of Measurements of Margins

Type of margin

Cross section

Dimension' (pm)

Dimension (mean ± SD [|imj)

55,9 52.4 57.9 54.4 53.8

54.9 ±2.1

Preoision errort (%)

Box-chamfered

Cusp-chamfered 62,3 59.4 62.4 6Q.4 64.8

Cusp-beveled

70.3 67.7 70.4 66.5 68.5 'Dimension = distance between the centers oí the uppermost and lowermost measurements in the 'Precision error (CV%) calculated as SD/mean dimension.

tapered shape ofthe graph, indicating a normal distribution ofthe measured points. The mean radius calculation ofthe phantom by scanning laser digitizer was 6.002 ± 0.015 mm. The system thus gave an SD of ± 15 |jm for each illuminated point on the phantom circumference. The precision error expressed as the CV% for the radius calculation of the phantom by the laser digitizer was 0.015/6-002 x 100% = 0.25%. The radius ofthe spherical steel phantom measured by microscope was 6.000 ± 0.01 7 mm. The precision error for the microscopic measurements expressed as the CV was 0.01 7/6-000 X 1 00% = 0.29%.

Measurements of Margin of tbe Phantom and Chamfered and Beveled Margins The mean dimension of 5 superimposed cross sections of repeated scans of the phantom was 43 ¡jm.

The results of the precision analyses of the measurements of the chamfered and beveled margins are shown in Table 1. With regard to accuracy SDs of the measurements ofthe margins ofthe box- and cuspchamfered margins and cusp-beveled margins were 19 pm, 21 fjm, and 24 \¡m, respectively, compared to 15 fjm for the margin of the phantomDiscussion Awareness of the favorable periodontai and functional aspects of cast gold restorations for the partial coverage of teeth has increased significantly during the last 30 years.'' A drawback of these restorations is the color of gold and the handmade production. All-ceramic

.Voljme 12, Numbers, 19!)9 399

computer-made restorations would be an alternativeA prerequisite for CAD/CAM construction of well-fitting partial-coverage restorations is a precise and accurate digital measurement of the margins ofthe preparation. Therefore, we felt it would be advantageous to test the hypothesis that measurements by a scanning laser 3-D digitizer are precise and accurate.

Stone dies ofthe preparations were used for surface measurements- The part ofthe stone die below the finish line was painted black so the computer cou Id automatically "grab" the finish line, instead of requiring the operator to trace it afterward on the screen with an input device such as a mouse.

Previous studies of computer-produced crowns have not attempted to evaluate separately the precision and accuracy of surface measurement.''^ Persson et al'' were the first to isolate the accuracy of a digitizer device consisting of a contact probe and a ball-shaped tip.

They measured the surface of a square gauge and found a maximum shape-related error of 10 |jm.

Persson and coworkers^-'concluded that their studies demonstrated that there is effective control of their digitizer process for complete-crown coping production.

We used an approach to assess instrument performance that uses precision and accuracy as the scientific rationale for evaluation-'*"''^ The stability of the measurements was controlled by measuring the phantom each day. The precision error for repeated measurements of the phantom was 0.25%. The measurements by digitizer and microscope ofthe phantom differed by only 2 pm. This slight difference might be partly a result of a difference in thickness ofthe white paint applied to the phantom surface.

The imernalionai lourndi of Prusthodontics

Margins ût Partial-Coverage Tooth Preparations for CAD/CAM

compatible with the CICERQ scanning laser 3-D digitizer. Currently tbis partial-coverage design is being tested for digitization by tbe Procera (Nobel Biocare) contact probe and bal 1-sbaped tip digitizer The preparation design was found fo be expedient for (he CEREC optical impression (Siemens), as could be i>;pected.

Measurements of chamfered and beveltd margins by a scanning laser 3-D digitizer are (1) precise (error < 4%) and 12) accurate, with an SD of less than 9 pm compared to optimal measurements of the spherical margin of the phantom.

The smaller SD for digitizer measurements also indicates that the digitizer technique is even more reliable than microscopic measurements. Our results are in agreement with those of Quick and Holtan,^ who compared the laser digitizer for analysis of dental materials with micrometer data and found that the digitizer SDs were smaller than 15 pm, well within the 40-|jm range of acceptable error for dental impression materials. Calibration of the digitizer by means of the spherical phantom just before each margin measurement ensured accuracy of the measurements of the comparatively irregular chamfered and beveled preparation margins.

Acknowledgments

The precision errors for the measurements of the boxand cusp-chamfered margins and the cusp-beveled margins were 3.9%, 3.4%. and 2.4%, respectively. The differences in measurement values and thus in the precision errors between the metal phantom and the stone dies are caused by 2 factors: fíjthe perfectly round surface of a spherical phantom is an easy surface for the laser beam to measure compared to the more or less irregular chamfered and beveled marginal preparation surfaces; and ¡2) there is a difference in optical texture of the different surfaces. The relatively rough surface of a stone die is diffusely reflective, in contrast to a smooth metal phantom that is fairly reflective. Quick and Holtan^ found that a difference in reflective (or absorptive] properties of surfaces resulted in different amounts of light being reflected from the laser to the CCD camera, and a longer time was required to read each data point; consequently, thetotal scan time was increased. A solution to this problem is the use of phantoms made of stone die maferiai. However, the shape of these phantoms is difficult to standardize and they are easily damaged.

The authors gralefully acknowledge Simon Vlaar and W i l j o de Ruiterfor the digitizer measurements and Jaap Reisig for the dental laboratory wori<, and loke Denissen-Gruter tor her heip in preparing the manuscript.

References

The accuracy of fhe margin measuremenfs was calculated by means of the SD (15 pm) of the measurements of tbe calibration phantom. As a parameter for comparison the dimensions of the cross sections of 5 superimposed measurements were chosen.

The dimension of the cross section of tbe phantom was 43 |jm and for the cross sections of the box- and cusp-chamfered margins and the cusp-beveled margins if was 55 ]jm, 62 |jm, and 69 pm, respectively.

ThecalculatedSDsfortbebox-and cusp-chamfered margins and cusp-beveled margins {19 pm, 21 pm, and 24 pm, respectively) were small.

It has been stated that the marginal fit of crowns is a decisive factor in any prosthetic fabrication system, whether it is based on conventional techniques or modern ones such as CAD/CAM.^ The clinically accepted standard for resulting marginai gap dimensions is 100 jjm."-''' In the CAD/CAM technique the marginal fit depends on the digitization of fhe surfaces of the chamfered and beveled margins. Our preparation design for partial-coverage toofh preparations was

The International lournal of Prosthodontics

1.

Van derZei|M.Cerarric-fii5ed-to-metal restorations with a new CAD/CAM system. Quintessence Inr 1993;24:769-778.

2.

Wahner HW, Steiger P, von Stetten E. Instruments and measurement techniques. In: Wahner iHW, Fogelman I (eds). The Evaluation of Osteoporosii: Dual Ereigy Absorptiometry in Clinical Practice. London: Martin Dunitz, 1994:14-34.

3.

Q u i c k D C , H o i t a n JR. Use of a s c a n n i n g laser threedimensional digitizer for analysis of dental materials. Biomed Instrum Technol 1991;25:60-67.

4.

Christensen C|. The coming demise of the cast gold restoration? |AmDentAssoc1996;127:l,233-l,236.

5.

Mormann WH. C A D / C A M in Aesthetic Dentistry. Beriin: Quintessence, 1996.

6.

Persson M, Anderssor M, Bergman B. The accuracy of a highprecision digitizer for CAD/CAM of crowns. I Prosthet Dent 1995:74:223-229.

7.

Anderssor M, Carlsson L, Persson M, Bergman B. Accuracy of machine milling and spark erosion with a CAD/CAM systerr. J Prosthet Dent 1996;76:I87-193,

8.

Ammann P, Rizzoli R, Siosman D, BonjourjP. Sequential and precise ir vivo measurement of bone mineral density in rats using dualenergy x-ray absorptiometry. | Bone Mirer Res I992;3:3I1-316.

9.

G r i f f i n M C K i m b l e R , Hopfer W, Pacifici R. Dual-energy ï-ray absorptiometry in the rat, Accuracy, precision, and measurement ofboneloss. I Bone Miner Res 1993;7:795-800.

10.

Sato M. Comparative x-ray densitometry of bones from ovariectomized rats. Bore 1995;4(cuppl¡:1 57-162.

11.

Denissen H, Veihey H, de Blieck |. Dual x-ny absorptiometry for alveolar bone: Precision of peri-implant mineral measurements ex vivo. ] Periodontal Res Í996;31:265-27O.

12.

Denissen iH, de Blieck |, Verhey H, Dual-energy x-ray absorptiometry for histologie bone sections. J Bone Miner Res 1996; 11:63e-644.

13.

McLean |W, von Fraunhofer JA. The estimation of cernent film thickness byan in vivotechnique.Br Dent J I971;13:1O7-111.

Karlsson S. The fit of Procera titanium crowns: An in vivo and clinical study. Acta OdontolScand 1993;51:I29-134.

14.

15.

400

Denissen H, Van der Z e i l , Reisig J, Vlaar S, De fiuiter W, Van WaasR, Computer copings for partial coverage. Int J Computer Dent (forthcoming).

!12, Number 5,1999

David Bartlett, BDS, PhD, MRD, FDS (Rest), RCS (Eng)' Keith Phillips, DMD, MSD^ Bernard Smith, BDS, PhD, MS (Mich), MRD, FDS, RCS (Eng), FDS, RCS (Fdin)<^

A Difference in Perspective— The North American and European Interpretations of Tooth Wear

Purpose: There is considerable interest in the European dentai research literature about the problem of tooth wear and specifically about dentai erosion, but this interest does not appear to be matched in North America based on the voiume of the literature there. The purpose of this article is to consider the possibie expianations for this difference.

Materials and Methods: This article examines the reasons for this disparity and attempts to explain the difference hy reviewing the North American and European literature on the etiology, pathogenesis, and prevalence of tooth wear. Results; It would appear from the literature that the reason for the difference in interest between the 2 continents is a reflection of how the appearance, etiology, and terminology are interpreted and used to define tooth wear, attrition, and erosion. Conclusion: Attrition is the wear of teeth against teeth; theretore, by definition any worn surface that does not contact the opposing tooth must have another etioiogy. An appropriate descriptive term is "tooth wear" when the etiology is muitifactorial or cannot be determined. A search of the literature shows more studies in the European literature of the etioiogy and prevaience of tooth wear than in the North American literature. The thrust of the European studies supports the view that erosion is more important than attrition in the etioiogy of tooth wear. Intj Prosthodont 1999:12:401^08.

Definition

M

uch of the emphasis on the nature of tooth wear in the European literature has recently been directed to erosion caused by dietary or gastric acids.

On the other hand, research from North America has appeared to concentrate on attrition as the predominant factor, with little acknowledgment of the role of acid erosion. Tbis difference will be explored by reviewing the etiology, prevalence, and appearance of erosion, attrition, and abrasion.

"Tooth wear" is an all-embracing term used to describe the combined processes of erosion, attrition, and abrasion, or when the specific diagnosis cannot be determined.' Erosion is defined as the chemical dissolution of teeth by acids other than those produced by bacteria, attrition is the wear of tooth against tooth, and abrasion is the wear of teeth by physicai means other than opposing teeth.^ The term tooth wear can be used as a generic description until a more 'Lecturer. Division af Consen/ative Dentistry, Cuy'i, King's and St specific diagnosis can be made; this is comparable to making the observation that a patient is pyretic and Tilomas' Denrai Institute. London, UK. Mssííl3n( Professor and Director, Graduate Prostbodontics, then moving on to a diagnosis of pneumonia and then University of Washington School of Dentistry, Seattle. Wasitington. investigating the cause of pneumonia. Some tooth "^Professor and i-lead, Division of Conservative Dentistry, Cuy's, wear continues as a slow process throughout life and King's and St Titomas' Dentai institute, London. UK. is normal, but in some individuals the rate increases Reprint requests: Dr David Bartiett. Fioor 25. Division oí to such an extent that the longevity of the teeth is Conservative Dentistry, Guy's, King's and St Thomas' Dentai compromised. The term "pathologic tooth wear" has institute. London Bridge. SEI 9RT. London. UK. Fax: + 44 been used to describe the state when the destruction 0719S5493S.e-niail:david.bartlettmkd.ac.uk

2. MumberS, 1999

401

The Inlern aliona i

alof Prosthodortii

North American and European Interpretations of Toolh Wear

impact on the teeth.''•' FHoidingor "swilling" carbonated drinks within the palatal vault may cause significant erosion, especiallyon the palatal/lingual surfaces of the maxillary anterior teeth, altliouiih erosion in this area is usually associated with •.>< id originating in the stomach,^"'''' There has been considerable interest in the link between dietary acids and dental erosion, but the evidence from studies that bave compared the severity of erosion with tbe consumption of acidic food and drinks is not conclusive. Most research on the role of dietary acids in erosion has been based in the laboratory.'^'''^ However, care should be taken when applying in vitro experimental methods to clinical problems. It appears from in vitro reports that dietary acids havethecapacitytocauseerosion of dentin and enamel,"''^'^^ but tbere are few published clinical trials on the effect of acidic drinks on teeth. A recent controlled clinical study by West et aP" compared the amount of erosion caused by orange iuice to water in volunteers from the staff of a dental hospital. Not surprisingiy, the orange juice was significantly more erosive than water. Thomas^' also investigated the effect ofdietary acids on volunteers and noted erosion in most subjects. Interestingly, some of the subjects who consumed high quantities of acids appeared to have marked erosion after 6 weeks whiie others with a similar diet did not. Thomas^' suggested that other factors such as drinking habit, the buffering capacity ofthe saliva, and the physical state of the teeth might have caused the difference in the degree of erosion observed in the subjects. Neither study used subjects with preexisting erosion, who might have been more susceptible to acids in the diet.

There is some epidemiologic evidence to support the hypothesis that diet is implicated in erosion.^^ Millward et al,^^ in an investigation of 100 schoolchildren, identified significant correlations between the reported consumption of acidic food and drinks and the prevalence of erosion. However, in a study of 210 schoolchildren in southeastern London, Bartlett et al^"* did not report statistical correlations between the prevalence of erosion and the reported consumption of acidic food and drinks. The data for thisstudy were collected during the summer and the correlations reported were in spite of the fact that the mean consumption of carbonated drinks was 3 to 4 cans per day. A problem with all of these studies is that data on diets relies on questionnaires, which can be notoriously inaccurate, especially in children.

The difference in appearance between eroded and noneroded enamel surfaces can be difficult to detect, especially in the early stages of erosion. Most prevalence studies on erosion have reported significant levels of enamel erosion and lower levels of more severe

of the teeth has reached a level at which restorations are indicated.^ Erosion

There are 3 main sources of acid erosion of teeth: dietary, gastric, and industrial acids.

Dietary Erosion

Darby"' reported the role of acids in the diet as early as 1892 when he described fruit juices dissolving teeth. Since that time many in vitro studies have investigated the acidity of food and drinks and their ability to erode enamel and dentin,'"" but the evidence from clinical studies remains poor.

Citric acid is found in citrus fruits and drinks and as an additive in carbonated drinks.'''^ It is one of the most potent erosive agents found in foods because of its ability to chelate calcium in hydroxyapatife, increasing the rate of dissolution. This ability to chelate hydroxyapatite is believed lo continue even after the piH increases at the tooth surface, thereby prolonging the erosion.^ Erosion caused by citric acid in the form ofvitaminC tablets and drinks has also been reported.'^''^ Other important dietary organic acids are commonly found in fruits such as pineapples, grapefruits, apples, cranberries, and black currants. Other dietary additives have also been implicated in erosion; these include phosphoric acid (found in some drinks), carbonic acid (found in all carbonated drinks), and others. The pH of some of these products falls below 4.0, which is recognized from in vitro studies as the approximate threshold for erosion to occur/''^ The carbonation ofthe drink is probably less important than its pH because carbonic acid is weak.^'' Carbonated water, therefore, is probabiy not particularly erosive, whereas carbonated lemon or cranberry juice would be more so. A popular drink in the United Siates is iced tea, which is normally served with a piece of lemon. While the tea itself would nol be acidic, the impact ofthe lemon—especially if the fruit is sucked or chewed—would have a greater potential for erosion.

Frequent consumption and the type of acidic food or drinks will to some extenl depend on where a person lives. Hotter climates necessitate a higher frequency and volume of fluid consumption and this may take the form of fruit juices or carbonated drinks.^^ FHowever, this ignores the influence of fashion and peer pressure on young people, which is associated with the consumption of carbonated drinks."' Not only is the type of acidic food or drink important, but the way it is consumed may have an

The International Journal of Prostliodontic^

402

Volume 12, Number 5,1999

Bartletteiai

North American and European inierpretations of Tooth Wear

erosion involving dentin.-^-^^ However, most of the statistical correlations related to the diet are based on minor enamel changes and these changes are especially difficult to differentiate from the appearance of uneroded tooth surfaces. Conversely, dentin exposure is much easier to diagnose but there is little evidence from the literature that erosion of dentin is correlated to tbe diet. Therefore, while it may be reasonable to conclude that erosion is sometimes caused by acidic food and drinks, tbe association with severe erosion has not been readiiy established.

Frosion Caused by Gastric ¡uice

Gastric juice has a pFH of around 1 and if it enters the oral cavity regularly the damage to teeth can be catastrophic. Oneofthe most powerful effects of gastric acid has been shown on the teeth of patients suffering from the eating disorders of anorexia and bulimia nervosa.-^ Typicaily, affected patients may induce vomiting to purge themseives of food or drink. The distinction between anorexia and bulimia can be unclear as some patients pass through episodes characteristic of both diseases. Frequent vomiting during pregnancy can have a similar effect.

The most important constituent of stomach juice is hydrochloric acid formed in the parietal cells lining the stomach walls and secreted in response to food.

The erosive potential of gastric acid is related to the time of consumption of food. Recently swaliowed food enters a highly acidic environment necessary for protein digestion. After some time the ingested food buffers the hydrochloric acid, reducing the erosive potential of the gastric contents.'^ If vomiting or regurgitation occurs soon after consuming food the gastric juice will have its greatest erosive potential, but if food is vomited later the gastric juice becomes less erosive. Acidic food and drinks are i<nown to provoke refiux and therefore have a greater potential to cause régurgitation erosion.^^ Régurgitation is an involuntary phenomenon whereby gastric acid passes into the mouth without conscious controi; unlike vomiting, it is not coordinated by the autonomie nen^ous system.^^ The regurgitation of gastric acid into the mouth is not normal and is associated with the condition known as gastroesophageal reflux (CER|.'^^ Heartburn is the most common symptom of GER and is caused by gastric acid that has leaked from the stomach, irritating the mucosal lining of tbe distal esophagus. In most people any leakage of gastric acid into the esophagus is temporary and the acid is quickly returned to the stomach by peristalsis. In others the acid remains for longer periods and symptoms become chronic and prolonged and patients require treatment. Other

íi(.ímo n

Numbers, 1999

403

evidence that regurgitated gastric juice causes paiatal erosion has been derived from research in chronic alcoholics and ruminants, in whom pathologic GER may aiso be involved.'"-^' Dental erosion has been identified in patients participating in upper gastrointestinal investigations for GER,-*- and GER has also been diagnosed in patients presenting with dental erosion."•^'' It appears that the 2 conditions are related and that régurgitation caused

by GER is responsibie for erosion in some patients.

There is also evidence that régurgitation erosion causes more extensive damage than dietary erosion.'

However, a history of heartburn and other symptoms may not always indicate the presence of GER. In an investigation of 36 patients presenting with dentai erosion 26 were diagnosed with GER using criteria developed by gastroenterologists.'^ Interestingly, 9 of these patients did not have symptoms of GFR; they are calied "silent refluxers." Therefore, the presence of dental erosion in these patients appeared to be a better indicator of GER than the disclosure of symptoms.

Gastroesophageai reflux is an important cause of dental erosion but is difficult to diagnose in some patients because of tbe lack of symptoms. Since the diagnosis of GER requires gastroenterologic investigations and the influence of dietary acids requires oniy a questionnaire, the iatter tends to receive more blame.

Industrial Erosion

The work environment has been reported to cause dental erosion. Historicaiiy, car battery workers, those exposed to industrial eiectrolytic processes, and others working with acids that are present as vapor in tbe air have suffered from dentai erosion.^^ Exposure of the teeth to acid continuousiy through the contaminated air produced erosive lesions similar in pattern to those caused by dietary acids. Improvements in occupational health and safety have made this type of

Attrition The constant rubbing of teeth against one another during routine function and during parafunction must be regarded as normal and the resuiting wear as part of the aging process.^' The amount of contact between teeth that normally occurs while eating a modern diet is probably insufficient to cause significant attrition even over a lifetime. However, frequent clenching or grinding ofteeth for purposes other than mastication (bruxism) may produce fiattened cusps.-'^•^'' Bruxism can occur during the waking hours or during sieep and, aithough common, may be regarded as abnormal if it damages teeth or produces symptoms.'^

The International Journal of Prosthodonlks

North Afneritan and European interprétations of Tooth Wear

identified in patients with bruxism, but it is often difficult to determine whether the intetierence caused tne bruxism or whether the interference was produced as aresultofthebruxism. Whichever is true, liriixismcan cause considerable damage to teeth that m.»y be made worse if teeth are restored with abrasive materials such as unglazed porcelain.

However, a close inspection of worn incisai edges often reveals areas of exposed dentin where the opposing teeth do not contact in any excursions (Fig 1 ).

This is common, especially in older patients, and cannot be entirely caused by attrition- Therefore, there must be some other explanation (this will be discussed later)- A useful diagnostic observation is whether the maxillary and mandibular occluding surfaces aie wearing at the same rate. If they are, this suggests attrition; if not, something else—usually erosion—must be accelerating the wear in one arch more than the other.

Fig 1 Wear of anterior teetti caused by a combination of erosion and attrition Ttie cupped out" incisai surface of the canine could not have been caused solely by attrition as the center ot Iha worn area cannot contact the opposing tooth.

Attrition produces wear facets on the occluding surfaces of teeth, including the incisai edges."" Tbis commonly begins soon after eruption or may start later in life. Eventually the cusps become flattened, the incisai edges are shortened, and dentin is exposed. Once dentin is exposed the wear resistance of the tooth is reduced and rate of wear is increased.'"

The distinction between damage caused by bruxism and by the normal aging process can be difficult to determine, especially in middle to late life, except in extreme cases.

The cause of bruxism is unknown, but Ramfjord and Ash"*^ described 2 possibilities- They suggested that the act of bruxism in some way relieves stress, eliciting some gratification; tbis could occur while asleep or awake. Alternatively, the process could be more mechanical. An occlusal interference may trigger a bruxing habit, producing attrition- To test this hypothesis Ramfjord''^ experimentally provoked bruxism in 10 Rhesus monkeys by placing high occlusal amalgam restorations in their mandibular molars.

The bruxing hegan immediately and continued unlil the amalgam was no longer high. The author considered that the cause of the bruxism was a subconscious effort by the monkeys to remove the high spots. Therefore, in the author's opinion the occlusal interference triggered the bruxism.

However, not all researchers agree with this concept. Rugh etaM* placed crowns with deflective contacts in 10 human subjects and reported that the interferences did not stimulate bruxism- The evidence based on these studies remains unclear as tbe reported studies used low numbers of subjects- There is some evidence to suggest that bruxism is a condition related to daytime stress or the anticipation of stress.""* However, a clear relationship between the 2 has yet to be proved. Clinically, occlusal interferences are

The tnternaiional lournal of Prosthodontii

Abrasion Abrasion is physical wear caused by materials other than teeth- Abrasion has been assumed to be associaled with over-zealous toothbrushing, especially along the cervical margins of the canines and premolars. Toothbrushing may or may not be the main factor as these lesions also appear on the lingual surfaces of molars and on lingually displaced teeth, where access by a brush is difficult- There is considerable debate but little scientific evidence on the etiology of V- and saucer-shaped cervical wear lesions and tbe less common vertical defects on the facial surfaces of posterior teeth.

Svinnseth et al''^ and Redmalm''^ believe that the mechanical action during toothbrushing combined with the abrasive in toothpaste causes abrasion. Lewis and Smith''^ argue that the process is more likely to be multifactorial, with erosion as tbe major influence. Acids present in the diet or originating from the stomach could weaken the tooth, making it more susceptible to abrasion.'"''

Abfraction is another popular concept. The wear is thought to originate from occlusal loads acting on teeth to produce minute stress concentrations around tbe cervical margin- Continual loading of the tooth will produce stress fractures called abfractions, which make the area more susceptible to erosion and abrasion.'"* Abfraction remains a controversial theory with little evidence to support its existence. A combination of factors seems the most likely explanation of these lesions.

The texture of food is thought to have caused abrasion in the past, although the abrasive influence ofthe modern Western diet is unlikely to be a significant

404

Volume 12, Ml

Banlett et al

North American and European Interpretations of Tooth Wear

factor. Bread containing grit from the millstone is thought to have produced abrasion/attrition. Today, in certain parts of the world, for example the Aborigines in Australia, people continue to have a high rate of tooth wear and abrasion; food is thought to be the cause.-'"'-'^

with unworn teefh released higher concentrations of calcium than the worn teeth. If is possible, therefore, fhat factors other than acids or attrition may be important in tooth wear, but as of yet research is not available to identify the effects of these factors.

Importance of Site and Pattern of Wear

Relative Importance of Erosion, Attrition, and Abrasion in Etiology of Wear

The sife of tooth wear can be used to some extent to suggest the source of the acid. Typically, but not always, acid originating from the stomach strikes the palatal surfaces otthe maxillary incisors, eroding enamel and in due course dentin. Possibly, in the early stages of fhe process the tongue protects the other surfaces of the teeth. As fhe erosive action persists the protective mechanisms of the mouth are overwhelmed and a more generalized pattern of erosion emerges, commonly affecting the occlusal surfaces of fhe mandibular molars, followed by the maxillary occlusal and posterior palatal surfaces.^^ The lingual surfaces of the mandibular teeth are seldom affected.

In 1984 Smith and Knight' reported that 35 of 100 consecutive patients with footh wear referred to a dental hospital for diagnosis and treatment planning suffered from erosion, while only 11 suffered from attrition, larvinen et al'''' reported similar findings in 1989 in a study on Scandinavian patients. Davis and Winter'" reported fhat a combination of erosion and attrition increased the rate of tooth wear fo a greater degree than if either factor was operating independently. Dental erosion in Europe is acknowledged to be the most cornmon cause of tooth wear, either independently as in eating disorders, or in combination with attrition or abrasion. The appearance of "cupped out" dentin on fhe incisai edges of anterior teeth or on the cusps of posterior teeth that do not contact the opposing teeth suggests a combination of erosion and attrition.

Dietary acids probably cause some erosion, especially in the young.-^-^ The influence of the diet is probably more important in the early stages of erosion than in more severe cases. This association is supported by the common use of acidic food and drinks in the Western dief.^'^^ Dietary acids are less likely to cause severe erosion; regurgitated gastric acid—with its lower pH and established association with eaiing disorders—CER, and other conditions are more likely to be the main etiologic factor,-•'•^' There have been few studies to investigate the effect of other factors on the etiology of tooth wear.

Gudmundsson et al^^ suggested that salivary buffering capacity might be important in dental erosion.

Further support for fhe role of saliva in erosion was reported by Milosevic and Dawson'^ when they compared flow rate and bicarbonate concentration in 9 bulimics. Interestingly, a few years earlier one of the same authors reported no association between saliva and patients with dental erosion and an eating disorder.^"* Some researchers have postulated that the abrasive surface of the tongue lying against the palafal sutfaces of the maxillary incisors may contribute to erosion.^^ Milosevic and Dawson^^ investigated the susceptibility of different tooth surfaces to erosion with an enamel biopsy technique. The results suggested that tooth surfaces have differing susceptibiliiies to erosion. Surprisingly, the enamel of the group

It has been suggested tbat sipping an acidic beverage will erode fhe buccal or facial surfaces of the maxillary incisors, and after prolonged use a more generalized pattern of erosion develops.'^ However, palatal erosion may also resulf if the beverage is held in the palatal vault or "swilled" around the mouth prior to swallowing.'" Therefore, although fhe pattern of erosion may be useful in identifying the source of acid it is by no means definitive.

Early enamel erosion is seen as smoothing of the minor enamel irregularities to produce a shiny, unstained surface. Once the dentin is exposed it erodes more quickly because it is less mineralized. As the denfin is exposed the foofh color changes from the creamy white of enamel fo fhe yellower color of dentin. In extreme cases erosion will result in the teeth becoming short and/or thin, and they may become level with tbe gingival margin. Ultimately the form of the tooth is lost and the function of the teeth impaired.

Hypersensitivity to temperature changes may be a problem with rapidly progressing erosion as the dentinal tubules are exposed to the oral cavity. However, if the wear is slow enough the pulp responds by forming secondary dentin and sensitivity is not a common problem even in severe cases, particularly in older pafients.

Prevalence of Tooth Wear Tooth wear is acknowledged to be an almost universal condition and part of the aging process.' In a study of 1,007 adult patients attending dental practices in southeastern England, Smith and

405

Á

Tiie International loiirnal of Pro^thodoritics

North Americün and European Inteipretation; of Toolh Wear

BartletLetai

progression of tootb wear using indices measuring occlusai wear.

reported that almost 98% had evidence of some tooth wear but only 3% to 5% of tooth surfaces in the younger age group had levels of wear that might necessitate treatment. FHowever, this rose to 8% to 9% in patients over age 5 6 . " Robb et al,^'^ in a controlied study on the prevalence of tooth wear in 151 Roman and Saxon skulls in Britain, reported that the condition is not a modern phenomenon; 30 skuils (nearly 20%) showed extensive tooth wear. Other European research by |arvinen et ai^'' reported that erosion was present on all teeth of 106 patients referred to a dental hospital. A better indication of the prevaience of tooth wear was reported by Linkosaio and Mari<kanen^^ in a random sample of Swiss adult patients. The amount of tooth wearvaried according to site and age, mostiy occurring on tbe facial and occlusai surfaces, while the ieast commoniy affected surface was the paiatal surface of the maxillary incisors. The largest pubiisbed survey on the prevalence oferosion wason 10,000 extracted teeth from southern California and showed that 18% of the teeth had evidence of erosion.^^ No clinical epidemiologic studies on dental erosion were found in the North American literature, but studies of the prevalence of erosion have been conducted on chiidren in Europe. In 1992 the UK National Child Dental Heaith Survey of 1 7,000 children reported tbe presence of erosion in 5 to 15 year olds.^^ The results showed that over balf of the 5 and 6 year olds had evidence oferosion in the deciduous dentition and in near iy a quarter of these dentin was involved. Palatal erosion was tbe most commonly affected site with 52% of incisors affected, while only 18% presented with buccal/facial erosion. In the permanent dentition dentin exposure was found in 2% of affected 13 to 15 year oids. Milosevic et al,^° reporting on 1,035 14-year-old children, observed that 30% had exposed dentin, mainly on the incisai surfaces. Millward et aP^ and Bartlett et al,^" in studies of 178 and 210 children, respectively, observed levels of erosion similar to those found in the UK National Child Denial Health Survey. As in the larger study the mosi commonly affected surface was the palatal surface of the maxiiiary incisors.

There is evidence in tbe literature to support these findings from North America, but unlike the European studies the incidence of attrition is reported. Sel igman etaP^reportüdtheseverityofattrition on the occlusai surfaces of study casts in 222 young adults by studying the appearance of the casts. Like Smith and Robb," Seligman et al observed (hat more than 90% of the subjects had evidence of wear, but a direct comparison between the 2 studies is impossible because each used a different method of assessment.

Silness et al*^' and Pintado et al^^ observed the

l of Prosthodonlics

Criteria for Assessing Prevalence of Tooth Wear One of the problems in attempting to record the prevalence of tootb wear is bow the condition is defined and what parameters are used to measure it. The evidence from the iiterature is confusing and difficult to compare. Some researchers have reported the prevalence of erosion,^'*'^^ some have reported the prevalence of tooth wear,''''^•*'' and to complicate the matter further, others have reported the prevalence of attrition.'^'^"^ The use of different terminology also confuses the interpretation of studies from tbe 2 continents and from different European countries.

Smith and Knight^ described a method for measuring tooth wear using an index to record the loss of tooth tissue on the lingual/palatal, buccal, cervical, and occlusal/incisal surfaces of teeth. Tbe index graded the degree of wear from 0 to 4 depending on its severity; 0 is defined as no wear, while 4 represents severe wear or pulpal exposure. This index was used to report the prevalence of tooth wear in 1,007 patients examined in gênerai practice in southeastern England as described earlier.*"^ In the UK National Child Dentai iHealth Survey^^ the authors used the Smith and Knight index but reduced the grading to 3 levels, making a comparison to the results of other studies on chiidren and adults difficuit.^^*''' In severai studies a diagnosis has been made and then an index used to record itsprevalence, for example, the prevaience of attrition on the incisai or occiusal surfaces of teeth.^''^^ Identifying the prevalence of tooth wear by specifying the etioiogy is hazaidous uniess individuai clinical histories of each patient are thoroughly investigated. This is not ai ways achieved. In 1988 Sei igman et al' ^ reported the prevalence of attrition recorded from study casts taken from 222 young adults and reported that nearly 92% had evidence of dentin exposure on their incisai or occlusai surfaces. Hugoson et al^^ reported simiiarly high levels of incisai or occiusal wear in 527 children. Although some of these authors used the term tooth wear in the titie of their articles, they used an occiusal score to record the severity of the wear, which ignores by definition ail other surfaces. This type of index excludes palatal/lingual wear, which is most commoniy associated with erosion.

It would appear that at least one group of North American researchers reported on the prevalence of erosion in their study of 10,000 extracted teeth.''^ However, on close inspection of the methodology the authors appear to ciassify cervical wear lesions as erosive in origin. The appearance of the cervical wear lesion has traditionally been associated with abrasion

406

North Americün and European Interpretations of Tooth We

and erosion rather than just erosion, an etiology that tends to be at some variance to the literature.

References

Early Tooth Wear as a Predictor of Later Susceptibility?

1.

Smith BCN, Knight |K. A comparison ot patterns of tooth wear with aetioiogical factors. Br Dent 11984:157:16-19.

2.

The glossary ct prosthodontic terms, ed 6. ) Prosthet Dent 1994; 71:43-112.

Smith BCN, Knight JK. An index for measuring the wear of teeth. Br Dent ) 19Ö4;1 56:435-438.

Darby ET. Dental erosion and gouty diathesis: Are they usually associated? Dent Cosmos 1892;34:629-640.

3.

An important factor in measuring tooth wear is the extent of damage. If dentin is exposed on the incisai edges ofthe maxillary anterior teeth in a 15 year old and the situation remains reiativeiy stable for the next 40 years it is unlikely to be a significant problem. However, if the wear continues and ultimately compromises the appearance and funaion of the teeth there is a problem. Most ofthe studies on the prevalence of erosion, attrition, or tooth wear report that early wear is common and severe wear, by comparison, is not.

There is some evidence that wear in the young may predict wear later in life. Knight et al'"' measured occlusal/incisai wear in the pretreatment and posttreatment records of 223 patients treated orthodontically. The authors reported that there were statistically significant associations with wear on the mandibular deciduous incisors and in the entire mouth of the same person asan adult. Pintado et aP^ measured wear over 2 years on 1 8 adults and also reported that attrition had progressed. The possibility that wear is episodic is supported by evidence that children pass through active phases of wear between the ages of 3 and 1 2 years and then the wear slows later in life.^^ If so, some of the high levels of erosion reported in children in the UK may later become inactive in adult life. Until a method is developed to measure wear, and in particular dental erosion, accurately this question will remain unanswered.

Conclusion Fundamental to interpreting the information from studies on tbe etiology and prevalence of tooth wear are the differences between erosion, attrition, and abrasion.

It would appear from the Furopean literature that the most common and destructive cause of tooth wear is erosion. Conversely, mostofthe prevalence studies in North America bave concentrated on attrition rather than tooth wear or erosion. It is only through a comprehensive history, studying the appearance of a wear lesion, and considering the etiology that a specific diagnosis can be properly made. If a specific diagnosis of predominancy erosion or attrition cannot be made despite a thorough investigation, then the descriptive term tooth wear should be used.

Perhaps the reason there is more interest in tooth wear, and in particular dental erosion, in Furope is that tbere bas been more research in Europe on the etioiogy and prevalence, much of it on children.

Volume 12, Number 5,1

4 5.

6.

7.

8.

9.

10.

11.

Asher C, Reid M|F. Early enamel erosion m children associated with ihe excessive consumption of citric acid. Br Dent J 1987; 162:384-387.

12.

Clurta |L. Denial erosion resulting from rhewable vilamin C tablets. I Am Deni Assoc 19li3;l 07:253-^^56

13.

Eccles ID, lenkms W C . Dental erosion and diet. | Dent 1974; 2:153-159.

14.

Milosevic A. Toothwear: Aetiology and presentation. Dent Update1998;25:6-11.

15.

Seligman DA, Piillinger AC, SolbergWK. The prevalence of dentai attrition and its association with factors of age, gender, occlusion, and TMJ symptomatology. | Dent Res 19e8;67:l ,323-1,333.

16.

KelleherM, Bishop K. The aetiology and clinical appearance of toothwear. EurJProsthodont Restorative D e m i 998;5:157-160.

17.

Bartlett DW. The causes of dental erosion. Oral Dis 1997; 3.209-211.

18.

Lussi A, Jaeggi T, Jaeggi-Scharer S. Prediction otthe erosive potential of some beverages. Cariei Res 1995;29:349-354.

19.

Lussj A, laeggi T, laeggi-Scharer S. The influence of different factors on in vitro enamel erosion. Caries Res 1993;27:387-393.

ZO.

West NX, Maxwell A, Hughes |A, Parker DM, Newcombe RC, A d d y M . A method to measure clinical erosion: The effect ot orange juice consumption on erosion of enamel, j Dent 1998; 26:329-335.

Thomas AK. Further observations on the influence of citrus fruit juices un human teeth. N Y State Dent j 1957;23:424-^30.

Johansson A-K, Johansson A, Biriihed 0 , Omar R, Baghdadi S, Carlsson G Dental erosion, soft-drink intake, and oral health in young Saudi men, and the development of a system for assessing erosiwanteriortooth wear. Acta Odontoi Scand 1996;54:369-378.

Millwanj A, ShawL, Smith A], RippinJW, Harrington E. The distribution and severity oí tooth wear and the relationship between erosion and dietary constituents in a gn^up of children. Int j Paedtr Dent1994;4:l5l-157.

21.

22.

23.

24.

Bartlett DW, Coward py, Nikkah C, Wilson RF. The prevalence of tooth wear in a cijsler sarrpie ot adolescent schoolchildren and its relationship wilb potential explanatory tactors. Br Dent I 1998;184:125-129.

25.

O'Brien M. Children's Dental Health in the United Kingdom 1993. London: Otficeof Population Censuses and Surveys, 1993.

Helistrom I. Oral complications in anorexia nervosa. Scand ] DentRes1977;85:7l-86.

26.

407

Crenby TH, Mistry M, Desai T. Potential dental effects of infanrs fruH d r i n b studied in vitro, Br| Nutrition 1990;64:273-283.

Crenby TH, Fhillipî A, DesaiT, MtstryM. Lahoralory sludies of dental properties of soft drinks. Br| Nutr 1989,-62;45I^64 Rytomaa I, Meurman | H , Koskinen |, Laakso T, Gharazi L, Tur jnen R. in vitro erosion of bovine enamel caused by acidic drinks and other foodstuffs. Scand ) Dent Res 1988 ;96;324-333.

Meurman | H , Harkonen M, iNaver H, Koskinen |, Torliko H, Rytomaa I, et si. EK peri menta I sport drinks with minimal dental erosive effett. Scand J Dent Res 1990;98;120-128.

Smith AJ, Shaw L. Baby fruit juices and tooth erosion. Br Dent] 1987;! 62:65-67.

Davis WB, Winter P|. Dietary erosion of adult dentine and enamel. Br Dent ¡ 1977;143:116-119.

The lnternation.il lournal of Prosthodontii

North American and European Interpretations of Toclh Wear

27.

28.

29.

Bartlett et al

Levine DF, Wiiigate DL, Pfeffer JM, Butcher P, Häbituiil ruminaticn: A benign disorder. Br Med J (Clin Res Ed) 1983; 287:255-256.

Bartlett DW, Evans DF, Smith BCN. Oral regurgiiation after refluï-provoking meals: A possihle cause of dental erosion?) Oral Rehabil 1997:24:102-108.

Bartlett DW, Evans DF, Srnilh BCN. Review: The relationship between g.istro-esophageal reilus disease and dentai erosion. ) Oral Rehabil 1996 ;23:289-297.

49.

50.

51.

52.

30.

Robb NO, Smith BCN. Dental erosion in patients with chronic alcoholism. I Dent 19B9;] 7:219-221.

31. Cilmour AC, Beckett HA. The voiuniary reilux phenomenon. Br D e n ! | 1994:175:363-372.

32. Jarvinen V, Meurman JH, Hyvarinen H, Rytomaa I, Murtoniaa H. Denial erosion and upper gastrointestinal disorders. Oral Surg Oral Med Oral Pathoi Oral Radiol Endod 1988;65:298-303.

33. Sctiroeder PL, Filier SJ, Ramirez B, Lazarchii< DA, Vaezi M f , Richter JE. Dental erosion and acid reflux disease. Ann Intern Med 1995:122:809-815.

34. Sartlett DW, Evans DF, Anggiansah A, Sniilh BGN. A sLudy oí the association between gastro-esophageal reflus and palatal dentalerosion. Br DentJ 1996:181:125-132.

35. Skogedal O, Silness], TangerudT, Laegried O, GilhLus-MoeO Pilot study on dental erosion in a Norwegian zinc factory.

Community Dent Oral Epidemiol 1977;5:248-251.

36. Petersen PE, Cormsen C. Oral conditions among Cernían battery factory workers. Community Derit Oral Epidemiol 1 9 9 1 : 19:104-106.

37. Berry DC, Poole DFC. Masticatory function and oral rehabilitation.] Oral Rehabil 1974;l:191-205.

53.

54.

55.

56.

57.

58.

59.

Woda A, Courdon A M , Faraj M, Occlusai contacts and tooth wear. ; Prosthet Dent 1987;57:85-93.

39. Xhonga FA. Brusism and its effect on the teeth. J Oral Rehabil 1977;4:65-76.

40. MolnarS, MckeelK, MolnariM, Prjybeck TR. Tooth wear ratci among contemporary Austraiian aborigines. J Dent Res 1983:62:562-565.

4 1 . Ramfjord S, Ash M Occlusion, ed 3. London: WB Saundeis, 1983:179-182.

42. Ramijord SP. Bruxism, a ciinicai and EMC ;tudy. | Am Dent Assoc i961;62:21-^4 43. Rugh ID, Barghi H, Drago C). Experimental occlusai discrepancies and noclurnal bruxism. J Prosthet Dent 1982:51:548-SS3.

44. Rugh ID. Psychological factors in the etiology of masticatory pain and dysfunction. Chicago: American Dental Association, 1983:85-94.

Milosevic A, Young P|, Lennon MA. The prevalence of tooth wear in 14-vear'old school chiidren in Liverpooi. Community DentHeailh 1994:11:83-86.

61.

Silness I, Berge M, lohannessen M. Longitudinal study of incisai tooth wear in children and adolescents. Eur J Oral Sei 1995: 103:90-94.

Pintado MR, Anderson CC, DeLong R, Douglas W H . Variation in tooth wear in young adults over a two-year period. J Prosthet DentI997;77:313-32O. Smith BCN, Bartlett DW, Robb N D . The prevalence, etioiogy and management ot tooth wear in the United Kingdom. | Prosthet Dent1997;78:367-372.

46.

47 48.

62.

63.

Svinnseth PN, Cjerdet NR, Lie T. Abrasivity of toothpastes. Acta Odontol Scand 1987:45:195-202.

Redmaim C. Dentifrice abrasivity. T h e u i e o f laser lighffoi dptermination of the abrasive properties of different silicas. An in vitro study. Swed DentJ 1986:10:243-250.

The Internat ion

i of Frost hod on til

64.

Knight D|, Leroux BC, Zhu C, Aimond |, Ramsey DS. A longitudinai study of tooth wear in onhodontically treated patients.

Am I Orlhod Dentofac Orthop 1997:112:194-202.

65.

Miilward A, Shaw L, Smilh A|. Dental erosion in four-year-old chiidren from differing socioeconomic backgrounds, j Dent Chiid 199S;61:263-266.

Lussi A, Schaffner M, Ho\a P, Suter P. Dental erosion in a popuiation of Swiss aduits. Community Dent Oral Epidemiol 1991; 19:286-290.

66.

Lewis K|, Smilh BCN. The relationship of erosion and attrition in extensive tooth tisiue loss. Br Dent] 1973:135:400^04.

Lee w e , Eakle WS. Possible role of tensile stress in the aetiology of cervical erosive lesions of teeth. | Prostiiet Dent 1984:52: 374-379.

408

Robb N D , Cruwys E, Smith BGN. Régurgitation erosion as a possible cause of tooth wear in ancieni British populations. Arch OralBion991;36:595-602 Jarvinen V, Rytomaa I, Meurman | H . Location of dental erosion in a referred population. Caries Res 1992:26:391-396.

Linkosalo E, Markkanen H. Dental erosions in relation to lactovegetariandiet. ScardJ Dent Res 1985;93:436-44I. Sognnaes RF, WolcottRB, Xhonga FA. Erosion-like patterns occurring in association with other dental conditions. J Am Dent Assoc 1972:84:571-576.

60.

38.

45.

Molnar S, Richards L, McKee |, Molnar I. Tooth wear in Australian populations from the River Murray Valiey. Am J Phys Anthropoi 19B9;79:185-196.

Jarvinen V, Rytomaa II, Heinonen OP. Risk factors in dental erosion. I Dent Res 1991:70:942-947.

BartleltDW, Smith BCN. The dental impact of eating disorders.

Dent Update 1995;21:404-t07.

Cudmundsson K, Kristletfsson C, Theodors A, Holbrook WP. Tooth erosion, gastroesophageal leflux, and saiivary buffer capacity. Oral Surg Oral Med Oral Pathoi Oral Radiol Endod 1995: 79:185-189.

Milosevic A, Dawson L|. Salivary factors in vomiting bulimics with and without pathological tooth wear. Caries Res I996;3O: 361-366.

Milosevic A, Siade PD. The orodental status of anorexics and bulimics. Bf DentJ 1989:167:66-70.

Smith BCN, Robb N D . The prevalence of tooth wear in 1G07 dental patients. ] Oral Rehabil 1996,23:232-239.

67.

Hugoson A, Bergendal T, Ekfeldt A. FHelkimo M. Prevalence and severity of incisai and occlusai tooth wear in an adult Swedish population. Acta Odontol Scand I988;46:255-265.

68.

Cash RC. Bruxism in children: Review of the literature. | Pedod 1988:12:107-127.

Voliime12,Nurrber5, t999

Wear Behavior of Precision Attachments

Manfred G. Wicbmann, DOS, Witold Kuntze, DOS''

Purpose: The purpose of this article was to compare the wear behavior of precision attachments with plastic inserts to conventional metal-alloy precision attachmentsMaterials and Methods: In a comparative study attachments of various designs were subjected to alternating load cycles in a wear simulator. In addition to conventional adjustable attacliments with metal-alloy matrix ¡ind patrix elements, attachments with feniaie elements that are lined with plastic inserts were investigated for the first time- In each wear test 10,000 separating and joining movements were performed in an axial direction under a continuous spray of artificial saliva at 37°C. Results: The attachments with metal surfaces shewed a rapid loss of approximately 60% of the required separating/joining forces during the first 1,000 cycles; after a further 9,000 cycles these forces fell to 25% and 35%, respectively, of the initial value. The attachments with plastic inserts, by contrast, showed only a 4 % and 8% loss, respectively, of the required ieparating/joining forces even after 10,000 wear cycles. With one attachment type a reproducible 20% increase of retention occurred during the testings. Conclusion: The precision attachments with plastic female inserts showed only negligibie amounts of wear and the most consistent retentive force in comparison with conventional precision attachments consisting of metal-alloy matrix and patrix components- Intj Prosthodont

1999:12:409^ 14.

A

ttachment-retained dentures represent one hightech solution to removable partial denture prosthodontics in both functional and esthetic terms.' ' The classic indication for precision attachments is in patients with natural anterior teeth and unilateral or bilateral posterior edentui ism for whom high esthetic demands must be met. In the majority of cases prefabricated precision attachments, wbicb

are available in great variety, are used.^ The basic classifications for attachments are precision/ semiprecision and intracoronal/extracoronal-''~^The precision attachment uses machined surfaces manufactured to very narrow tolerances. The semiprecision attachment differs in the fabrication method. In most cases matrix and patrix are cast components using prefabricated plastic parts as patterns. In combination with a cast lingual bracing arm, wbich reduces the wear on the attachments significantly/ precision or 'Assistant Medicai Direaor, Deportment of Prosthodontia. semiprecision attachments represent a considerably Medical University of Hannover, Germany. rigid system.^'^ The side walls provide lateral force M55/sMnt Professor. Department of Prosthodontics, Msdicsl transmission and rotation control; the gingival floor University oí Hannover, Germany. provides occlusal force transmission.'^''° The retention Reprint requests: Dr Manirea C- Wichniann, Corl-Neuberg-Strasie of an attachment-retained partial denture depends f, D-J0625 Hannover. Germany. Fax: + 49 511-532-4778. eon static and sliding friction between matrix and maii: mw@prothetik.zmii.mii-h3nnover.de patrix."''^ The precision attachment should have Tbi; psper was presented in part at the annuai meeting of tbe a minimum height of 5 mm fo satisfy functional Internationai Association for Dentai Research, ¡une 1996, Nice, requirements such as retention, bracing, and France.

409

l of Proslhodorlii

Wichmann/KuntïË

Wear Behavior of Precision Altatiiments

support,"''^ Wear-induced material losses at the atfachmenf surfaces occur during insertion and removal of the partial denture as well as during minimal movements under functional load as a result of friction between the female and male éléments, leading to a loss of retention.'^ Tbe extent of wear depends on the material and the design of the precision attachment. Thus, alloys with a high gold content seem to tolerate a larger number of separating/joining movements with less wear than, for example, alloys containing nonprecious metals.''' The film of saliva between matrix and patrix acts as a protective layer and lubricant that reduces wear,'^"^ Wear at the attachment surfaces leads to a long- or mid-term loss of partial denture retention,'^ To counteract this undesirable effect most precision and semiprecision attachments can be adjusted to restore wear-induced losses of friction. This is achieved by design elements such as latches, partial or completely slotted male parts, setscrews. or exchangeable parts. [n addition to fhese conventional attachments precision or semiprecision attachments with exchangeable plastic inserts that line the matrix element are becoming increasingly available. However, their wear behavior has not yet been determined in clinical studies, with the exception of one preliminary study indicating precision attachments with plastic matrix inserts to be advantageous compared with conventional metal precision attachments."

Wear-induced loss of retention in attachmentretained dentures poses a major clinical problem. For this reason the choice of an attachment type essential ly depends on which design provides the best conditions, ie, the least wear, to ensure long functional life.

In view of the large number of precision attachments currently on the market few studies are available on their retention and wear behavior.'^-^^ In fact, no comparative investigations at all are available on fhe wear behavior of precision or semiprecision attachments with exchangeable or adjustable plastic matrix inserts.

The aim of fhe present study was therefore to investigate the wear behavior of attachments with plastic inserts in comparison to conventional metal-alloy precision attachments.

I ^

Fig 1 a Metal attachments tested: McCollum attachment, left, and tJltraTec attachment, right.

common connecting elements in use in Germany.^' Tbe SC precision attachment (Cendres & Métaux) is an extracoronal adjustable device, the female element of which is lined by a plastic insert (Fig 1 b). A set 5crewallowsfhepressurewith which the female part encloses the male part to be adjusted. The Mini SC-F (Cendres & Métaux) and the Preci-Vertix (Cekal attachments are extracoronal devices in which exchangeable plastic layers of various size are used in the female elements to vary fhe retention force (Fig 1 b). The plastic insert is made of Galak (Cendres & Métaux), a polyoxymethylene (polyacetal) homopolymer plastic. The Preci-Vertix attachment, the only semiprecision attachment investigated in fhis study, uses prefabricated plastic parts as patterns.

The plastic insert is made of polypropylene.

Materials and Methods A total of 5 attachment types representative of different attachment construction designs was selected for the study. The well-known McCollum (Cendres & Métaux) and UltraTec (SITec) precision attachments were used as reference devices (Fig 1 a). Both devices feature metal-alloy female and male elements. Both are intracoronal, adjustable precision attachments, the McCollum attachment being one of tbe most

lof Prosthodontics

410

In a wear simulator in which a play-free linear slide was moved in finely defined intervals by means of a computer-controlled stepper motor, 6 separating and joining movements each minute were executed in the axial direction under a spray of warm OZ^C), finely filtered artificial saliva (10 mL/min) consisting of bisodium hydrogen phosphate 0.5 g/L, potassium bihydrogen phosphate 0.5 g/L, tartaric acid 0.75 g/L, acetic acid 0,6 g/L, lactic acid 0.8 g/L, sodium chloride 0.58 g/L, and bisodium ethylenediaminetetraacetic acid (EDTA) bihydrate 1.86 g/L at a pH of 5.25. In each cycle the female and male parts were fully separated.

A force sensor in tbe setup measured to within 0,02 N tbe force required to join and separate the female and male parts simultaneously during the test cycles.

Wichmann / Kuntîe

Wear Behsvio, of Precision Atfachmenls

Fig 1 b Attactiments with plastic matrix inserts testöd (left to right): Mini SG-F attachment, SG attachment, ana Preci-Vertix attachment.

With tbe belp of a parai leiometer the female and maie parts of tbe attachment under examination were cemented in a precise axial direction in the premilied mounts of the wear simulator using an autopoiymerization composite resin ¡NimeticCem, Espe). Thus, errors caused by casting or soldering were avoided. The adjustable attachments were set at a retention force of 7 Nat the start ofthe experiment.^"'Both the McCollum and the UltraTec attachments with metal-alloy female andmaleelementshad to be adjusted at tbe start to obtain a retention force of 7 N since the required joining and separating forces are less than 3 N upon delivery from the manufacturer. For attachments for which the retention force could be varied in rough increments by using different plastic inserts, those that yielded tbe value most closely approximating 7 N were used.

Five specimens of eacb attachment were subjected to tbe wear tests. These consisted of a total of four consecutive cycles of 10,000 separating and joining movements eacb. After every ten cycles the maximum force needed to separate the attachment was measured and recorded. Thus, curves in Figs 2 and 3 are each based on 1,000 measured values. The results were statistically analyzed with SPSS for Windows, version 6.12 and Excel for Windows, version 6 (Microsoft]. The arithmetic mean, the standard deviation, and the 95% confidence interval were determined for each attachment type. A more detailed statistical analysis was not possible because of the heterogenous nature of the groups. A scanning electron microscopic (SEM] examination of tbe attachments before and after the tests provided information on the condition of their surfaces and the presence of specific signs of wear.

- - Numher5, 1999

411

Results During the first 1,000 cycles of the wear test the McCoilum attachment (Fig 2) showed a mari<ed initiai increase of the separating and joining forces, followed by a rapid fail of 3 to 4 N. With the UltraTec attachment this increase was minor (Fig 2]. During the foilowing 9,000 test cycles there was a further slight decreaseto values of between 2 and 3 N, withsiightly higher values for iJltraTec. In contrast to the metal attachments a slight increase of the required separating force from 7.5 to 8.5 N was found during the first 200 test cycies with all SG attachments. The values then gradually returned to the initial level during the next 2,500 test cycles.

Thereafter the retention force remained almost constant up to the 10,000th test cycle (Fig 3).

With the Mini 5G-F attachment with the red plastic insert ("normal retention"] initial retention values of 11 N were measured. The required mean separating force increased to 14.4 N during the first 1,000 test cycies, after which it declined steadily to 13.2 N by the 10,000th test cycle although it remained above the initial force of n N (Eig 3|.

With thePreci-Vertixattachmentfitted with the yellow insert ("normal retention"] the retention force increased from 14.8 to 17.2 N during the first 60 test cycles. Subsequently the retention force decreased steadiiy to reach 13.6 N after 10,000 cycles (Fig 3].

Examination of the matrix and patrix surfaces by SEM showed marked signs of wear in the metal attachments, eg, detachment of metai particles and tbe presence of grooves and scores (Fig 4). In contrast, all attachments with plastic inserts showed minimal signs

The Internat i oral lournal of Frosthodontics

Wear Behavior of Precision Attachments

Wichmann / Kuntze

Fig 2 Cun/a through the means ot tfie requireO separating and joining torces tor each of 5 McCoilum and UltraTac attachiments dunng 10,000 test cyoles.

No. of loading cycles

Fig 3 Curve through the means ot the required separating and joining torces tor each of 5 SG, Mini SG-F, and Preci-Vertix attachments during 10,000 tesf cycles.

Force (N)

18 17 16 15

7 6 5' 4 3' 2-

— ss — Mini Se-F — Prsci-yertI»

^^

o

o

o

o

o

No. cf loading cycles

of wear on the insert surface ¡n the form of fine grooves that ran perpendicular to the load direction (Fig 5).

retention force of 7 N' set at the start of the tests was selected in accordance with the retention forces required to maintain a removable partial denture in place.^^-™ The resu Its of the tests on 5 attachments of one type showed a small standarddeviationaswellasanarrow 95% confidence interval as a result of the good reproducibility of the measurements. The wear behavior of the attachments with metal surfaces agreed with the results of earlier investigations.'""''' The results of our investigation also confirmed the results ofthe only earlier investigation'^ indicating that precision attachments with plastic matrix inserts show reduced

Discussion Long-term wear tests of attachments were carried out in an in vitro setting to permit comparison under standardized conditions. Our choice of 10,000 repeated test cycles was based on the assumption that a partial denture is removed and replaced 3 limes daily for cieaning.'^''' Thus, the number of test cycles corresponds to a clinical life of approximately 10 years. The

412

Volumel2, Number 5,1999

Wichmann / Kuntze

Wear Behavior of Precision Attachments

Fig 4 SEM view ot ttie mais element ot a McCoilum attachment after 10.000 test cycies Signs ot coarse wear w, h materiai ioss can be seer> on the side of the adjustable slot, especialiy at the edges of the male hT 40 1 longitudinal grooves and scores. B a r . 1 mm. ¡Original magnification left x 2i •

Fig 5 SEM views ot the fetnale element Ota Mini SG-F attachment atter 10,000 test cycles. Only the surface otthe plastic insertshows very slight signs ot wear in the tormot tine grooves perpendicular to the load direction. (Original magnification x 40.)

wear compared with conventional metal precision attachments.

We intentionally avoided para-axial loads, which would be expected to occur in clinical use, to obtain an isolated conclusion regarding the wear behavior of plastic-metal friction pairs used in attachments with plastic inserts. However, a follow-up study will investigate the influence of para-axial forces on the fit of the attachments used.

The reproducible initial increase of the retaining force in one attachment type with a plastic insert (Mini SG-F) was probably caused by swelling as a result of 0.2% water absorption at 23°C and/or thermal expansion of the plastic on being warmed to 37"C. In the case of the melal attachments the initiai increase was conceivably caused by seating processes in the metal surfaces.

12. Number 5, 1999

Compared to the attachments with plastic inserts, which tolerated 10,000 test cycles with no appreciable loss of retention, the attachments with metal surfaces showed substantially greater wear. This is consistent with the clinicai observation that attachment-retained dentures suffer a loss of retention in the short to mid term. Even if—contrary to expectations—the attachments with plastic inserts were to exhibit a Ioss of friction in clinical use because of influences that were not simulated in the in vitro test (eg, aging of the plastic), the initial friction could be readily restored by replacing the plastic inserts during routine checks. The results of the wear tests were confirmed by SEM examination of all attachments. Without exception the surfaces of the metal attachments showed marked signs of wear (Fig 4), which were absent on the attachtTtents with plastic inserts (Fig 5).

413

The Inttrnationoi Journal of Prosthodonlies.

Wear Behavior of Precision Aitdthments

Wiclimann / Kuntze

There may also be an aspect of patient comfort with attachmentsconsistingofplastic matrix inserts, as these devices do not twist and they permit gentle denture insertion and removal with perceptible friction. A disadvantage of attachments with plastic inserts is their periodontally unfavorable extracoronal arrangement compared to an intracoronal arrangement, in contrast to the Preci-Vertix attachment the SC and especially the Mini SC-F attachments have sides facing the mucous membrane that are so smooth that no corners or angles form, thus providing acceptable periodontai conditions. Nevertheless, patients fitted with these attachments should be made aware ofthe necessity to clean the cavity between the extracoronal male element and the mucous membrane to prevent periodontai damage.

Conclusions • Precision and semiprecision attachments with plastic inserts showed continuous friction in the in vitro wear test even after 10,000 test cycles.

• SEM examinations revealed no signs of wear on attachments with plastic inserts.

• With metal precision attachments the friction fell by approximately 60% within the first 1,000 test cycles and by up to 80% after a further 9,000 cycles.

• SEM examination revealed pronounced signs of wear on precision attachments with metal female and male components.

• In terms of the wear factor investigated in this study, attachments with plastic matrix inserts seem to be recommendable for clinical use.

The authors would like to thank Ceka (Antwerpen, ßelgiumi. Cendres & Métaux IBiel, Switîerland), Degussa (Hanau, Germany], and SiTec (Cevelsberg, Germanyl for their generous supportof fhis study.

References 1.

3.

Graber G. Color Atlas of Dental Medicine: Removable Partial Dent jres. New York: Thjeme, 1988.

Preiskel HW. Precision Attaciiments in Dentist^, ed 3. St Louis: Mosby, 1979:95-97.

Zahler|M. Intracoronal precision attacfiments. Dent Clir Nortli

The Iniernalional lournal of Prosthodontics

Stiittgen U. E x p e r i m e n t e l l e U n t e r s u c h u n g z u m VerschleiEverhalten der dentalen Gußlegierungen Degulor M, Micro-bond-NP2 and W i r o n 77 unter spezieller Berücksichtigung des Teleskopsystems. Dtsch Zahnarztl Z 19B3;38: 1,024-1.025.

Stüttgen U. Zum Einfluß dei Speichelschmierung auf e>iperim e n t e l l e erschleilSunteisuchungen an EM- und NEMGußlegieruiigen. Zahntechnik 1 9 8 5 ; 4 3 : 4 6 6 ^ 7 1 .

Kragelski IW. Reibung und Verschleiß. München: Hanser, 1971. ¡ung T, Borchers L. Experimentelle Studie über mechanische Eigenschaften von Präzisiorsverbindungen. Dtsch Zahnarzt! Z 1983;38:986-989.

Besimo CH, Egii B, Sener A, Graber G, Gysin R, Fischer J. Konfektionsgeschiebe in der Teilprothelik. Phillip | 1995;12: 591-596.

Besimo CH, Bichweiler UM. Experimentelle ünteisuchungen über die Eigenbeweglichkeit konfektionierter intrakoronaler Profilgeschiebe. Z Stomatol I987;84:391^O4.

Koeck B, Grüner M, Werner BE. Vergleichende Untersuchung einiger vorgefertigter Verbindungselemente bei paraaxialer Belastung. Dtsch Zahnarztl Z 1993:48:622-624.

Sauer G. Vergleichende Untersuchung der gebräuchlichsten prothetischen Hilfsteile. Dtsch Zahnarztl Z 1976;3I:542-546.

Steward BL, Edwards RO. Retention and wear of prec i si er-type attachments. J Prosthet Denl 1983;49:28-34.

Friedrich R, Kerschbaum TH. Petraitis D. Der Parodontalzustand von Halte- und StùtZïahnen nach Anwendung intra- und extrakoronalerVerbindungselementefür Freiendprothesen. Dtsch Zahnarztl Z 1988;43:542-546.

Acknowledgmerits

2.

Am 1 9 8 0 ; 2 4 : l 3 i - 1 4 1 .

Berecca G, MacEnlee MA. Classification of precision attachmcnl;. J Prosthet Dent ] 987;589:322-327.

Burns DR, Ward JE. A review of attachments for removable partial denture design: Pari 1. Classification and selection. Int | Prosthodont l990;3:9e-IQ2.

Baker HL, Goodkind RJ. Theory and Practice of Precision Attachment Removable Partial Dentures. St Louis: Mosby, 1981.

Coye RB. Precision attachment removable partial dentures. | Calif Dent A55OC1992;20:45-52.

Gro55er D. The dynamics of internal precision attachments. | Prnsthet Dent 1953;3:393-4O1.

Zinnci ID. Locking types of semiprecision attachments. Dent Clin North Am l985;29:81-96.

Singer F. Improvements in precis ion-attached removable partial dentures. ; Prosthet Dent I967;1 7:69-72.

Zinner ID. Precision attachments. Dent Clin North Am 1987; 31:395^16.

Zinner ID. Prefabricated metal intracoronal semiprecision attachments for removable partial dentures. Int | Prosthodont 1989:2:357-364.

Finger IM. Trouble-shooting, repairs, and relining. Dent Clin North Am1985;29:199-214.

Caldwell RC. Adhesion of foods to teeth. J Dent Res 1962;14: 168-171.

414

Voiume 12, Number 5, 1999

Vincent ¡ardel, DCD, DU' Michel Degrange, DCD, DSO, DEO'' Bernard Picard, DCD, DSO^ Gérard Derrien, DCD, DSO, DEC/'

Surface Energy of Etched Ceramic

Purpose: !n a previous arficie the authors examined the evolution of the bond strengths of 2 dental feldspathic ceramics. The objective of the present study was to evaluate the effect of surface modifications with hydrofluoric acid gel (concentration 10%) on the surface energy of 2 dental feldspathic ceramics (GC and PVS). Materials and Methods: For an energy characterization, 30 sarrples of CC and 30 samples of PVS were built. This study comprised the measurement of contact angles to determine the work of adhesion (W^) of the 2 ceramics. The evolution of the work of adhesion depended on the action of the hydrofluoric acid gel on the roughness of the surface of the 2 ceramics. Results: In a polished stafe PVS presented a higher work of adhesion than CC. Etching the ceramics with hydrofluoric acid gel increased the work of adhesion, especially for CC, but this treatment was not sufficient to obtain a high work of adhesion. Conclusion: Etching with hydrofluoric acid gel was not sufficient to raise the work of adhesion of fhe 2 ceramics.

Silanizafion is preferable to etching, int¡ Prosthodont I999;19:415-4i8.

B

ond strength is provided by a combination of physical, mechanical, and chemical factors.'"^ The physical component is dependent on the surface State of the substrate, which can be characterized by its surface energy. Natural or artificial alterations (etching, silanization, etc) of this surface increase or decrease the surface energy and the adhesion. Thus, activating the dental enamel byacidetching increases its suriaceenergy, while topical application of fluoride reduces it.•''" Energy characterization determines the sutface energy of a substrate such as dental tissue or biomaterial, enabling adhesive potential to be evaluated. The scale factor is traditionally assessed by measuring the contact an-

gles of various reference liquids with the surfaces tested.

Ideally these should be planar, low energy surfaces. This is rare for dental surfaces and biomaterials such as ceramics, which exhibit the topographic defects associated with highly polarized, high surface energy, A liquid can be partially or totally spread over the surface of a solid, D jpré's and Young's equations characterize these phenomena.'^ " Dupré's equation determines the work of adhesion as a function of energies (Fig 1 ):

where W^ = work of adhesion, y^^, = free energy oi solid's surface, y^^,, = surface tension of liquid 'Aisociate Professur, Department of Prosthodontics, Facuity of balanced with its vapor tension, and75j = interfacial energy.

Dentistry, Brest University. France. ''Professor and Director. Laboratory of Biomaterials, Faculty of Young's relation describes the equilibrium of a Dentistry. Paris V University. France. drop of liquid on a solid as a function of 3 interfacial '^Professor and Director. Laboratory of Biomaterials, Faculty of energies (y^^,, y^y,, and y^¡} expressed as a function Dentistry. Paris VII University, France 'Professor and Director, Department of Prosthodontics, Facuityof of the contact angle 6 (Fig 11'^^'-'O' ' : Dentistry. Brest University, France.

Reprint requests: Dr Vincent¡ardei. J Rue Amiral Lacaze, 29200 Brest, France, e-maii: Vincent.Jardei&univ-breit.fr

¡2, Numbers, t999

415

The International

i at Prosthodontics

Surface Ener¡;y of ttfiied Ceramic

Table 1

Jartlei et al

Product Specifications

Product

flanutacturer

GC ceramic

GC Dentai

PVS ceramic

SS White

Hydrotluortc acid

Symphyse

Specifications Feidspalhic ceramic for iniays and porcsiain laminate veneers Feldspathic ceramic tor inlays and porceiain laminate ueneers Concentration = 10%

Fig 1 Dupré's equation determines the adhesive ettort as a function of energies: yg^,,. = tree energy of soiid's surface, yi_y.. = surface tension of iiquid balanced with its vapor tension, and •lgi_ = interfaciai energy

Fig 2 G1 Krüss instrument for oonfaot angle measurement. C = camera; Sy = synnge that delivers calibrated drops of reference iiquid; O = position of observer, observer, and and measurement measurement of of the the contact act angle angle of of the the drop; drop; G G= = magnitying magnitying giass, giass, F F= = tioodliglit; tioodliglit; R = oom i with temperature and pressure stabilized; d = drop of reference lliquid d (distilled ( d i t i l l d water); t ) Sa S = sample le of cen ceramic ramic.

where 6 = contact angle and lie = spreading pressure [generally ignored when low).

Measurement of a contact angle for a liquid with a known y¡_y, provided the VV, value for a material, in this case 2 feldspathic dental ceramics with a iow density of crystalline fillers and a large vitreous pbase (CC ceramic |CC| and PVS ceramic [SS White], Tabie 1 ).

Materials and Methods

SY-G-92-04372

between etching, siianization, and bond strength for the 2 feldspathic ceramics GC and PVS.'-^ The present study consisted of an energy characterization comprising measurements of contact angles to determine the differences in the evolution of surface energy between poi ished and etched states of the 2 ceramics. The contact angle measurements were recorded with a G1 Krüss instrunient (Zeiss]. In a room where temperature was stabiiized at 37°C and pressure was kept at 1 atm, a drop of liquid with a standardized volume was positioned on the surface of the ceramic disk of the sample; the contact angle was measured 5 seconds later (Fig 2).

Distilled water was selected as the reference liquid to monitor the contact angle's evolution depending on roughness and to determine the W^ value for each ceramic. At first, 15 samples of GG ceramic (group A) and 1 5 samples of PVS ceramic (group C] were built. After firing and removal of excess material, the thickness of the ceramic mass was adjusted on a Struers dap-u polisher (D-8950, Biberach/Riss].

Eacb ceramic-tipped rod was positioned perpendicuiar to the surface of a 220-grain abrasive disk that turned at 300 rpm and was constantly irrigated with water to prepare a flat, normai ceramic surface. The choice of etching time and hydrofiuoric acid gel concentration depends on the authors. Chen et aP^ used a hydrofluoric acid gel concentration of 5% for only 2 minutes. Generally the concentrations of acid gei have varied from 7.5% to 10%; tbe etching time also ranged widely, from 2 to 10 minutes."'-^''Once polished, 15 samples of GC ceramic (group B] and 15 samples of PVS ceramic (group D) were etched [5 minutes) with hydrofluoric acid gel (Table 1 ) as in the authors' previous mechanical and topographic study.'^ After polisiiing or etching each sample was subjected to measurement in airofthe contact angle. The l-l/j values were then determined for all sampies:

Eor an energy characterization, 30 samples of GC ceramic and 30 samples of PVS ceramic were randomly divided into 4 groups of 15 sampies; group A = polished samples of GC ceramic, group B = etched samples of GC ceramic, group C = polished samples of PVS ceramic, and group D = etched samples of PVS ceramic.

These2-part(metaliic and ceramic) sampies were fully described in a previotjs article on the relationships

\ nf I=ro51hodomit

171061

509815

W , = -y^^,(l -H Cos6] 4-ne ríe was ignored, and for distilled water ~ii^^- 72.6 A statistics software package (Stat View I), Brain Power) on a Macintosh PowerBook 1400cs/166

416

Volume 12,

lardel e[ ¿i\

Surface Energy of Elchcri CersmJc

Table 2

Results of Energy Characterization Study*

Group

Ceramic

H (degrees)

A B

C D

GC (polishsd) GC (etched) PVS (polished) PVS (etched)

CosH

(mJ/m^)

Mean

SD

Mean

SD

Mean

SD

58.3 15.7 57.6 2O.d

3.2 3.3 5.4 2.9

0.5 1 0 0.5 0.9

0.05 0.02 0.08 0.02

110.7 142.4 111.4 140.6

3.4 1 1 5.9 1.3

'Rtleen tesis foi eacn group SD = standard deviation.

(Apple Computer) was used for a one-way analysis of variance (ANOVA) and a Scheflé test at a 95% confidence level for all results.

a W, (or polislied GC and PVS • W^ for elclied GC and PVS 150-

Results

140-

Results from 60 contact angle measurements and W determinations are presented in Table 2. For GC and PVS ceramics there was a significant difference (P< 0-0001) between the groups: A (CC poiished) ^ B (GC etched), A (GC polished) ¥^ D (PVS etched), ß (GC etched) ^ C (PVS polished), and C (PVS polished) ^ D (PVS etched). Polishing and etching produced a significant difference in IV^ for the 2 ceramics. Figure 3 illustrates that when polished, PVS ceramic has slightly greater adhesive potentiai than GC ceramic.

Etching increased the adhesive potential for GC and PVS ceramics; etched GC ceramic's adhesive potential was the highest but there were no significant differences between the W^ values of etched GC and etched PVS.

130-

11010090GC Ceramic

PVS

Fig 3 Values of work of adhesion (IV,,) tor each group of GC and PVS ceramics in poiished and efched stales.

retaining the bond integrity of 3 glass ceramics (Dicor IDentsplyl, Mirage [Chameleon Dentai], and Vitabloc |Vita|).-' These results are different from those of this study because in the present study 2 modified feldspathic ceramics with a iow density of crystalline fillers and a large vitreous phase were used; the microstructure change is probably differenf for modified feldspathic ceramics and glass ceramics. The mechanicai factor is affected by ciinicai conditions and the preparation's geometry. The chemical factor can provide large-scale changes in bond strength as demonstrated in our previous study highlighting silanization.'Application ofthe silane bonding agent to the porcelain affer hydrofluoric acid etching appeared to be suitabletbrachieving consistent bonding between the composite resin and

Discussion We can note that for both GC and PVS ceramics surface energies are close both for polished and etched state5 (Table 2). Etching increases the VV^ by 29% for CC ceramic and by 26% for PVS ceramic. Thus, etching has a rather limited influence on surface energy evolution. Comparison with mechanical adhesion testi described in a previous study gives identical results, since the following adbesion values'-were obtained using the same bonding material: 8.3 ± 2,4 MPa for GC ceramic after polishing alone; 11.6 + 5.0 MPa forCC ceramic and after etching alone; 6.1 ±2.6 MPa for PVS ceramic after polishing alone; and 11.2 ±3.3 MPa for PVS ceramic and after etching alone.

Clinical Implications

The physical factor of adhesion represented by W^ for GC and PVS ceramics is weai<ly modified by etching with hydrofluoric acid. Thus, etching does not appear to be the best surface treatment to obtain strong adhesion for CC and PVS ceramics. In a recent study the authors demonstrai;ed that acid etching was the single most effective procedure for enhancing and

VumberS, 1

C -

A.E

This study on the evolution of energy potentials for CC and PVSceramicsdemonstrated the slight increase in surface energy following etching with hydrofluoric acid for both ceramics. Tbe ciinicai step of etching internal prosthetic aspects can be considered of use in

417

The Inlernalional loiirnal of Proîtliodonlics

Surface Energy of Elched Ceramic

reconstituting inlay-onlay type surface treatments and facets. After etching, rinsing, and drying thesilanization of the internal aspect must be completed with a dual-component silane (nonhydrolyzed): optimal chemical coupling with bonding materials must also be ensured.'^'-^ On a practical level the roughness of the ceramic substrates obtained by hydrofluoric acid etching coupled with the use of silane has proven necessary' to obtain the maximum adhesive potential al the level of the bonded ceramic joints.

11.

13.

14.

15.

16.

17.

References 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

n.

18.

BuquetJ. Bonding to dentine. Acta Odontol 19Ö4;147:435-452.

Panighi M, C'SellC. Physico-chemical study of dental surfacesand mechanisms of composife adhesion. | Biomater Dent 1993; 6:61-70.

CraigRC, Peyton FA, Restorative Dental Material, ed 5. St Louis: Moshy, 1975.

Attal I-F, Edard V, Degrange M. Factors modifying the accuracy of free energy surface measured by contact angle method. J Biomater Dent 1990;5:] 43-155.

19.

20.

21.

Attal J-P, Degrange M. Relationships between dentin adhesion and bond strength of three bonding systems. | Biomater Dent 1991:6:3-17.

Bouter D, Tirlet G, Degrange M. Performance of sandblasted ! i tanium tor resin bonded technique. J Biomater Dent 1994;9:65-74.

Charrier JL, Hachom C, Sigot-Luisard MF, Degrarige M. Roughness, surface energy and organocypic culture. | Biomater Dent1993;8:11l-I17.

DegrangeM, SadounM, Heim N. Dental ceramics, part II; New ceramics. | Biomater Denn987;3:61-69.

Degrange M, Ramspacher V, Wehbi D, Roques-Carmes C Topographic approach to the interfaces between dental stone and class A algmates. | Biomater Dent 1985;! :263-275.

Degrange M, Baran G, Wehbi D, Roques-Garmes G. Evaluation of adhesion of 5nOj treated metal frameworks (OVS) with the sessile drop technique. J Biomater Dent 19B7;3:109-11 5.

Degrange M, Bouter D. Faclors infiuencing the reliability of resin-bonded fixed partial dentures. In: Degrange M, Roulet|-F {eds). Minimally Invasive Restorations with Bonding. Ciiicago: Quintessence, 1997:53-176.

Literature

22.

23.

24.

25.

26.

27.

23.

lardel V, Degrange M, Picard B, Derrien G. Correlation of topography to bond strength of etched ceramic. InL J Prosthodont 1999:12:59-64.

Ghen|H,MatsumuraH,AtsutaM, Effect of different etching periods on the bond strength of a composite resin to the machinable porceiain. J Denl 1998:26:53-58.

CalamialR. Etched porcelain veneers: The current state oi the art. quintessence Int 1985:16:5-12.

CaiamiaJR. Materials and technique for etched porceiain facial veneers. Acta Odoritol 1983:31:48-51, Calamia |R. Glinical evaluation of etched porcelain veneers. Am J Denl 1939:2:9-15.

Calamia JR. Anterior and posterior high resistance bonded porcelain. Clin Odontoi 1990:11:53-63.

Horn HR. Porcelain laminate veneers bonded to etched enamel.

Denl Clin North Am 1983;27:671-685.

Mink JR, Timmons JH. Laminate veneers. Dent Glin North Am 1984;28:187-2O3.

Nakabayashi N. Effectiveness of 4 META/MMA-TBB resin and resin-bonded fised partial dentures. In: Degrange M, RouletJ-F leds). Minimally Invasive Restorations with Bonding. Ghicago: Quintessence, 1997:177-183.

Nation W,Jedrychowski!R, GaputoAA. Effects of surface treatments on the retention of restorative materials to dentin. | Prosthet Dent 1980,44:633-641.

NowiinTP, Barghi N, NorlingBK. Evaluation of the bonding of three porcelain repairs systems. J Prosthet Dent I981;46:516-518.

Perelmuter S, Montagnon |. Reinforced jacket crowns. Cah Prothese 1901,36:97-109, Perelmuter S, Launois G. Bonded laminate veneers. Inform Dent 1937:1:13-21.

Stangel I, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. | Dent Res 1937;66:1,460-1,465.

Tjan AHL, Nemetz H. A comparison of the shear bond strength between two composite resins and two etched ceramic materiais. Int I Proslhodont 1988:1:73-79.

Roulet |-F, Soderholm KJ, Longmate |. Effects of treatment and storage conditions on ceramic/composite bond strength. J Dent Res 1995:74:381-337.

Chen | H , Matsumura H, Atsuta M. Effect of etching period and silane priming on bond strength to porceiain of composite resin.

Oper Dent 1998:23:250-257.

Abstraet-

Location of the hinge axis and the kinematic centre in asytnptomatic and ciicking temporomandibuiar joints.

An optoelectronio jaw-movement recording system was used to record opening/closing movements in 10 asymptomatic subjects and 30 subjects with a ciicking ¡oint. Movement paths of the hinge axis and the kinematic axis were caicuiated. On average, locations ot the hinge axis and the kinematic center did nol ditter signiticantiy tor the symptomatic subjects, but the mean difference between the locations was 5 mm {individually up to 9 mm). For the group with ciicking joints there was a significant difterence between the hinge axis and the kinematic axis ot 9 mm (individually up to 24 mm). The hinge axis may be a practicai reference point tor the reconstruction ot movements of casts in an articuiator, but this study indicated that it should not be used tor the study ot condyiar movements. Based on the resuits the auttiors suggest that for this purpose ttie kinematic center should be used.

CaticA, NaeijeM.J Ora/f?e'iaM1999;26:661-665. References: 2B. Reprints; Dr M. Nasije, Department Ot Oral Function. Section CMD, Academic Centre tor Dentistry Amsterdam, ACTA, Louwesweg 1,1006 EA Amsterdam, The Nellierlands. e-mail: m.naeiie@acta.nl—/IW

The Internationa i lourn^i of

418

Voiume 12, Numh"

Integrated Electromyography of the Masseter on Incremental Opening and Closing with Audio Biofeedback: A Study on Mandibular Posture

Martin D. Cross, BDS, LDS, MSc' Zeev Ormianer, DMD'' Kobi Moshe, DMD' Esther Gazit,

Purpose: The purpose of this study wns to test the hypothesis of a minimum electroruyographic (EMCI rest position based on masseter surface EMG recordings of incrementai opening and cicising of the tnandible with simultaneous audio EMG bioteedback. Materiab and Methods: Nineteen alert subjects in an upright seated position opened and closed the mandible in 1-mm increments 20 mm interincisai iy. An eiectronic recording device aiiowed each subject to maintain the vertical dimension of each increment whiie simultaneously reducing right masseteric muscle activity to the minimum possible levei using audio EMG biofeedback. Integrated EMG masseteric activity was recorded at each static opening and closing increment. Results: A mean plateau of integrated EMG output for all subjects with no minimum EMG point or circumscribed minimum EMG range for any of the nineteen suhjects was shown. Analysis ot" variance tor repeated measures showed no difference in opening and closing EMG ieveis I P = 0.27| and no interaction between opening, ciosing, and change in vertical dimension {P< 0.00011. Conclusion: These results, with those cf other studies, raise questions regarding tlie validity' of the concept of a unique physiologic rest position of tiie mandible with the masseter or associated muscles at minimum muscle activity. The idea of overiapping postural ranges appears to be more appropriate, / n t / Prosthodont 1999;! 2:419-425.

T

However, controversy remains regarding the ability to define and clinically measure a repeatable postural relation that fits this role. Mandibular posture occurs at multiple possible instantaneous positions constantly moving in response to such factors as changes in pos^Sen/or Ciinicai Lecturer and Director of Graduate Prostbodontics, ture, respiration, swallowing, pressure, !ip compeDepartment of Prostbetic Dentistry, Tbe Maurice and Gabrieia tence, and speech.'

Goidschieger School of Dentäi Medicine, Tel Aviv University, israel.

Physiologic rest position, as defined in The ^Instructor, Department of Prosthetic Dentistry. The Maurice and Glossary of Prosthodontic Terms, occurs when the asGabriela Goldscbleger Scboot of Dental Medicine. Tei Aviv University, israei, sociated musculature is in a state of tonic equilibrium '^Resident. Department of Orai Surgery, Chaim Sheba Medicai or minimal contractural activity.- This assumes that Center, Tel Hashomer, Israel, tn partial fulfillment of DM0 tbesis. physiologic rest position is a specific position and that School of Dental Medicine, Tel Aviv University. ''Associate Professor and Cbsirman, Department of Occlusion and there is a single position of minimum tonic elevator contractural activity. There has been disagreement as Behaviorai Science, The Maurice and Gabriela Goldschieger Scbool of Dentai Medicine, Tel Aviv University, Israel. to whether minimum electric activity occurs at a specific ÂĄaw separation or over a range of vertical Reprint requests: Dr Martin D. Gross, Department of Prosthetic heights.^ Dentistry, Scbooi of Dentai Medicine. Tel Aviv University, Tel he postural rest position ofthe mandible continues to be used as a vertical reference relation for restoring the occlusal vertical dimension in prosthodontics.

Aviv, Israel. Fax: -t 972-3-6409250.

Tbis paper was presented at the 7tii meeting of tbe international College of Prosthodontists. October 1997. Malta.

419

Physiologic rest position is thought to be distinct from the more cranially related clinical rest position, a repeatable ciinicai reference relation with an

rhe tniernatioral lojrnal of Prosthodontics

Masseter EMG on Opening iird Cloiins witii Biofeedback

Table 1 Vertical Mandibular Relations and Ranges Reported in the Literature for Dentate Subjects No. of interocclusal resf ubiects space (mm)

study Clinical rest position Garnick and Ramlicrd 1962'' Rugh and Drago 19B1' Wessbergetal t983= Peterson eial 1983' Peterson et al19B3' Van Sickles et al 1985'° Grossand Ormianer 1394'^ Michelotlietal 1997'^ Michelottietal 1997" Minimum EMG rest position Rugh and Drago t 9 8 1 ' Manns et al 13B1 'Peterson ef al 1933' Peterson ef al 1983' Van Sickles ef al f 985'° Plestietal19aB'" Pleshetal19aB"' Pleshetal19SB" Pleshetali9aB"' Michelotfietal1997'ä Minimum EMG resting range Manns etal 1 9 8 1 "

Majewsky and Gale 1984'^ Majewsky and Gale 1984'^ Pleshetal19S8" Plesh etal 1988" Micfielctfietal1997'= M ic fiel off i ef al 1997^^

1.7 ± 1.28

to 4 10 10 12 8 40 8 8

2.1 2.5 ±1.2 4.6 ±1.42 3.2 ±1.09 3.2 ±2.1 2.6 ±0.33 1 4±1.1 2.0 ±1.3 08±C8

10 8 4 10 10 12 9 9 9 9 40

8,6 (range 4.5-12.6) 10 5,3 ± 1.9 High mandibular plane angle 9.7 1 4.24 9.95 ± 2.09 Low manditsular plane angle Opening sequence 1C.1 ± 3 6 Opening sequence 9.2 ± 3.9 11.9±6.1 Olosing sequence Opening sequence 6.1 ± 2.2 B.3 ± 3.5 Olosing sequence Opening sequence 7.7 ± 2.7

NSF Massefer NSF NSP NSP NSP Msssefer Massefer NSF NSF NSF

12.5 Opening sequence 12-19 15 5 Opening sequence 6-1B 4-16 4-16 10 8 ±4.4 Opening sequence 103±44 Closing sequence 4-18 Opening sequence Opening sequence 4-1S Opening sequence !-19 Olosing sequence 1-19 2.t2±0.74 2,9 5,2 ±1.5 2.6 ±1.5 betöre TENS 3.4 ±1.9 alter TENS 4.4 ± 0.Ë7 3.1 ± 0.04

Anfenor temporal

8

22 22 9 9 40 40 19

Present sfudy Van Mens and de Vnes 1984 ' 60 George and Boone 1979" 14 Wessberq ef al 1983^ 4 62 Koncfiakef al 19B8^° Gross and Omianer 1994'* Ormianer and Gross confroi 1996" Manns etal 1990'* Maximum bite force relation Storey 1962™ Garren etal 1964*" Manns and Spreng 1977^^ Manns et at 1979» MacKenna ana Turker 1983" Lindauerefal 19915«

Command, phon etic, -» NHR, EO, MD swallowing -»HHR,EO* Phonetics tNHR, E O * Phonetics Phonefios -»HR. E O » Phonefics -•HR. E O » Phonefics -» HR » Command -* HR. EO * Phonefics -» HR. E O » Phonetics -•HR, E O » Phonetics -•HR,EO»

20

8

Manns efal 1981'^

Mefnoa

8 8 12 3

6

Low mandibular plane angle High mandibular plane angle Long lace Low mandibular plane angle Higfi mandibular plane angle

Posterior femporal Anterior temporal NSF Anterior emporal Anterior emporal Massefe Anterior emporal Mass efe Massete Anferior emporal

1 1 T

1

Mandible static on Incremental opening or closing sequence

1 i

Bioteedback

T

TENS-induced rest position

•* NHR, EO * § BFB -•HR, EC » 5 ITR t NHR, E 0 * § -» EO * § ITR -» EO * § ITR -•HR. EO§ITR -• HR, EO * 5 ITR -» HR, E 0 * 5 ITR -• HR, EO * § ITR -»HR, E 0 * 5 I T R -» HR, EO * § ITR -•HR, EC»§ITR ^ H R . E C » g ITR ^ H R , EC, MD§ -»HR. EC, MD§ ->HR, EO#§!TR -» HR, EO * 5 ITR -•HR, E O * § I T R -•HR,EO*§ITR -• HR, EO * § BFB -• HR, EO * 5 SFB -»HR, EO» -*NHR* t hJHR, E O * -» HR, EO *

J_

Deep relaxation -•HR, E 0 * § (relaxed -»HR, Ë 0 * § resting poStu e) Hypnosis -» HR, EO »

8.9 17.5 17-27 20 15-20 17 15-20

T

Mandible stafic on incremenfal opening or closing sequence

Constant bite lorce/minimum EtulG

T

1

Maximum bife force relation

1 Minimum EMG submaximal bite lorce

1

-* i sitling erect; NHR = no headrest, EO - eyes open, MD = meclianical device measured interocdiusal rest space: * = electronic inlerocclusal rest space assessment; t = standing erect; HR = headrest; » - skin-point measurements; NSF - nonspecitic facial muscles; § - incremental study; BFB = bicfeedback relaxation at static increments; ITR = instructed to relax at static increments; EC = eyes closed; TENS = transcutaneous electric nerve stimulation.

interocclusal rest space (lORS) range of 1 to 4 mm (Table 1). Clinical rest position is registered immediately following cranial relation of the mandible by phonation, swallowing, or tooth closure.•*'" As the musculature h further relaxed the mandible assumes a more open range of positions. Relaxed resting mandibular posture has been associated with a point or range of minimum electromyographic (EMG) activity/''-'•'as established with transcutaneous electric

The Intern.iliongI lournal of ProstliodtiiiLii

420

nerve stimulation (TENSI,^''^ hypnosis,'** biofeedback,'' and relaxation techniques.'^''^ Findings of a vertical postural zone of suppressed elevator EMG activity during slow closure*'^"^"^^ and at static increments'''^"'"' suggest that physiologic rest position occurs within a postural range, the width of which varies among studies.''-^-^''^'^^ A circumscribed point of minimum surface EMG activity was reported for masseter and nonspecific facial

VolLimel2, Numbers. 1599

Masseter EMG on Opening and Closing with Biofeedbaci<

muscles and termed the minimum EMG rest position (MERP).-"•""- Other studies have shown a minimijm EMG resting range (MERR) for elevator muscles.'-"'""-' These ranges showed variations between opening and closing recording sequence and variations between different recording protocols (Table 1 ].

Difficulties have arisen in attempting to measure static posturai positions of minimal muscle activity.

To record minimum EMG activity at a particuiar vertical relation a spatial recording device is necessary to aid a subject in achieving and maintaining a desired degree of interocclusal separation.

Using such a device tbe subject has to alternately activate depressors and elevators to maintain this vertical relation during recording of the EMG activity. While this is being done the mandible is not in a true relaxed resting relation. Attempts have been made to overcome this by prerecording relaxation training and by instruction to relax at each static increment.^-'"'- '•*•-' Rugb and Drago' used simultaneous visual biofeedback with a kinesiograph oscilioscope.

A greater variation in the rest position foiiowing biofeedback has been reported by Van Mens and de Vries.'" Mean pubiished vaiues of clinical rest position and MERR (Tabie 1 ¡ and a previous study''' indicate tbat overlap often occurs between clinical rest position, MERR, and relaxed resting posture, suggesting that minimum masseter EMG may be independent of vertical dimension with suitabie relaxation. If an effective relaxation tecbnique is used at consecutive static or closing increments a subject shouid be able to reduce EMG levels to minimum levéis for each postural relation. This is inconsistent with the notion of a unique minimum EMG rest vertical dimension.

The purpose of this study was to test the hypothesis of MERP based on surface masseter recordings by measuring masseteric EMG ievels at successive 1 -mm vertical opening and closing increments of mandibular posture, using botb visual feedback to maintain the postural vertical relation and simultaneous audio EMG biofeedback to minimize EMG levels at each increment.

Measurement System Each subject was seated vertically and comfortably in a dental chair with a headrest and instructed to keep the eyes open and to look directly ahead.

Surface bipoiar eiectrodes (triple silver chioride electrodes, | & ] Pouisbolwere adhered to tbe facial skin.

Electrodes were piaced over the right masseter in the general direction of the muscle fibers at a consistent position measured to be in the middie of the superficial part of the masseter at the level of the occiusal piane. The skin was cieancd with alcohol and eiectrode gel conductive paste was appiied. The eiectrodes were connected to an EMG recording system (Atlas 8600, Physioios) with an audio biofeedback channel. The EMG unit was connected to a computer capable of storing continuous EMG signais. Tbe EMG recording equipment had a 0.25-|jV root mean square noise level specified by the manufacturer with a 100to 200-Hz bandpass. The 5-pV range was used to detect differences in the 1 to 2 pV range. The noise ievels and bandpass of the equipment used by Rugh and Drago'were similar to those used in this study (Rugh ID, personai communication, 1989]. The EMG unit is routinely used in research and ciinicai application and was regulariy serviced to ensure reliabiiity of the EMG output. Interocciusal rest space measurements were made using an iORS-recording device that has been previously described.'^ Subjects were abie to depress and elevate the mandible and simultaneously observe the digital display to an accuracy of 0.001 mm.

Biofeedback Training and Recording Before each recording session subjects were encouraged to reiax and were trained to reduce the tone of tbe audio EMG channel to consistent minimum levels. When a minimum level of EMG activity was achieved repeatedly over 5 minutes it was recorded as the baseline minimum EMG levei forthat subject.

This procedure was repeated 5 times and the mean value was recorded. Subjects then learned to depress and elevate the mandible in 1 -mm increments using the visual digital dispiay. They then learned to maintain each ievel of open ing and to simultaneously reduce the audio EMG tone to a minimal level for 5 to 10 seconds at each increment. At the start of the recording sequence subjects were encouraged to reiax using the audio feedback. When this reached the baseline EMG ievel the recording was initiated and marked on the screen at 3-second intervals.

Subjects then lowered the mandible by 1 mm, holding this position using the visual digital recorder display and simuitaneously reducing EMG tones to a

Materials and Methods Subjects On tbe basis of availability and compliance 19 dentai students (12 men and 7 women, mean age 28) were selected. All bad intact stable dentitions and were free of signs and symptoms of temporomandibular disorders. Exclusion criteria included sensitivity to digital pressure of right and left masseter and temporal muscles, lateral temporomandibuiar joint aspects, and limitations of movement or joint sounds.

12. Number 5,1999

421

lo Lima i oí Proîthodontics

Masseler EMG on Opening and Ciosing with Biofeedbiick

Cross el a Fig 1 Mean integrated EMG values at static increments of vertical jaw separation with audio bioteedback. Vertical lines = standard deviaticn.

5'

• Opening sequence n Ciosing sequence

4'

>

3'

LU

2-

1 •

0' 2

3

4

5

6

7

3

9

10

11

12 13

14

15

16 17

IS

19

VeriLcal jaw separation (mm)

These findings show no circumscribed minimum EMG point or range for 1 -mm incremental opening and closinginany of the 19 subjects. The small EMG range of A 0.2 pV to A 0.5 pV showed the repeatability of EMG levels.

minimal level. The operator initiated the 3-second recording period when the digital positioning device reading stabilized at each increment. Consecutive 1-mm increments were recorded in an opening sequence up to an lORS of 20 mm followed immediately by a ciosing sequence in 1-mm increments back to intercuspation. The EMG data for each recording period were processed as the mean vaiues with standard deviations for the consecutive readings in each 3-second recording interval.

Statistical analysis was carried out using anaiysis of variance (ANOVA) and covariance for repeated measures.

Discussion The results of this study show a piateau of EMG values that is distinctly different from the point of minimum masseteric and facial EMG activity (MERP}.^'^i°'i2 These results indicate that for the methodology used minimum masseteric muscle activity does not occur at a specific resting vertical dimension when effective masseteric muscle relaxation is achieved at measured increments.

Efforts to reproduce and measure the glossarydefined physiologic rest position- as a repeatable MERP correlating tonic resting elevator EMG activity with successive incremental vertical postural relations have shown conflicting and inconclusive results. A specific vertical relation of minimum integrated EMG (MERP) has been shown for the masseter and nonspecific facial muscles.'''*''"'^-^ Noncircumscribed ranges of minimum EMC (MERR) have been reported for the anterior and posterior temporal muscles'''•^^ and for the masseter.^^ The anterior temporal has been described as the muscle most active and sensitive to changes in postural relations.^"*'^^ For the glossary definition of physiologic rest position to be valid, one would expect to see an MERP for the anterior temporal as well as for the masseter, which is not the case.'^-^^ Minimum EMG ranges of elevator muscles have been described during continuous slow opening and

Results

Figure 1 shows the mean integrated masseteric EMG values for 19 subjects on incremental mandibular opening and ciosing. Both opening and closing graphs show a distinct piateau of masseteric EMG levels from intercuspation to 20 mm of opening for both opening and closing increments. There was no specific minimum pointor range of suppressed EMG activity evident in any subject.

ANOVA for repeated measures showed no statistical difference in opening and closing (EMG, P = 0.27) and no interaction between opening, closing, and change in vertical dimension (P= 0.45). Mean opening and closing values were 2.08 ± 0-52 (JV and 2.14 ±0.5 pV, respectively. Mean baseline minimum EMG was 1.85 ± 0.87 |jV, range 0.4 to 2.85 pV. For opening increments the recorded range between maximum and minimum values was 0.5 [JV and 0.2 ^iV for closing increments.

Tlie Inlernationai

1 of Prusthodontics

422

Masseter EMG on Opening and Closing with Biofeedback

closing movements of the mandible.^'^û'^i'^^ Garnick and Ramfjord-' report a range of minimum dynamic elevator activity during 11 mm of uninterrupted slow opening 3.8 mm from intercuspation. This was described as "a resting range" of the muscles during continuous slow movement and has often been misquoted as the postural resting range of the mandible, implying a range of static resting mandibular posture.

Static incremental studies show both circumscribed points and noncircumscribed ranges of minimum

The mechanism and level of minimum tonic resting EMG varies with menial status, affecting recording levels of mandibular posture. Taylor" attributed tonic baseline EMG to tonic stretch reflex unitary firing of Type I fibers in deep masseter and anterior temporal muscles, with background motor neuron excitation and tonic firing in the static fusimotor system.

In sleep and during anesthesia contraction of the jaw elevator muscles is reduced or abolished as primarily the elastic forces of inert muscles and connective tissues^'^^'^^-^'' support the mandible. The level of tonic EMGactivity can vary from minimal levels during general anesthesia, sleep, hypnosis, autogenic relaxation, biofeedback, or relaxation to relaxed or stressed vigiiance.^-'''^^-'^'^"^ Variations in body posture, eye closure, and environmental light levels reduce anterior temporalis and masseter resting EMG levels.^'^^'^' The validity of comparing normative EMG values"*^-^^ with myofascial pain-dysfunction and craniomandibular disorder groups''-^^ has been questioned.''^*'' Curiously, no reference is made to recording vertical dimension in these studies.'"^' Thus, the concept of a unique physiologic rest position based on minimum masseter and associated muscle activity as discussed above is not well supported by the findings ofthe present study and related literature. Difficulties arise in its definition, recording, and measurement. Physiologic rest position is subject to variables of recording technique, EMG and lORS recording equipment, degree and method of muscle relaxation, mental state of the subject and variation between muscles, prior jaw motion, and even the subjectivity of the observer.^•''^ While mandibular posture is continuously moving, 3 distinct recordable vertical ranges emerge from the dental literature; clinical rest position (1 to 4 mm), MÍRP to MERR (3.5 to 12 mm), and maximum bite force relation (5 to 22 mm),^'"^^ with various degrees of overlap (Table 1 ). Clinical rest position is recorded as the mandible is relaxed immediately following phonation, swallowing, or tooth closure, or combinations thereof.*-^''^••'^'"^•''^ As the musculature is further relaxed from clinical rest position, the mandible assumes a more open range of positions that depends on the relaxation and recording methods used (Table 1).

The findings of this study show that with audio feedback minimum masseter EMG levels close to prerecorded baseline levels were achieved independent of vertical dimension and opening or closing sequence.

This is in contrast to studies finding an MERP for masseter and associated muscles. These and inconsistent findings of other studies indicate that previous definitions of rest position as a unique postural relation at minimal contractual activity are inappropriate; the idea of overlapping ranges may be more realistic.

G 7 5 " > i 2 i 4 2 3

With an electrode configuration recording nonspecific facial muscles a mean MERP of 8.6 mm on static opening increments (range 4.5 to 1 2.6 mm) was shown by Rughand Drago/Manns et aP- reporta circumscribed MERP of 10 mm for the masseter.

Majewsky and Gale^^ show a noncircumscribed MERR for masseter and nonspecific facial muscles, while Michelotti etal-^ reportan MERR for masseter and anterior temporal muscles (lORS) of 4 to 16 mm and MERP for nonspecific facial muscles. A significant difference in masseter MERP is reported by Plesh ct al'-* between an opening sequence (lORS) at 5 mm and a closing sequence (lORS) at 15 mm. The same was seen for nonspecific facial muscles, indicating that MERP measured in this manner is subject to prior jaw motion. Minimum muscle activity also occurs at different vertical relations for different muscles.^^•''' Manns et al'- reporta minimum EMG point of 10 mm for the masseter, a minimum EMG range MERR at 13 mm of opening for the anterior temporal, and an MERR at 16 mm for the posterior temporal muscle.

Differences between our findings and tho.se cited above may be caused by differences in relaxation protocol infiuencing the degree of control in muscle relaxation at each static increment Manns et aP^ used no FMG relaxation feedback and no vertical positioning aids. Plesh et aP"" and Michelotti et al^^ used instructions for muscle relaxation and a kinesiograph for vertical positioning. Majewsky and Gale^^ used instructions to relax aL increments and a mechanical vertical measuring device, while Rugh and Drago' used simultaneous visual feedback for relaxation and vertical positioning. The findings of Plesh et al'* of the effects of prior jaw motion suggest that insufficient muscle relaxation occurs at sequential increments.

The after effect of muscle spindles was used to explain the difference in EMG recordings and MERP between incremental opening and closing sequencesJ"*'^^"^' Biofeedback as used in the present study—acting via tbelimbicandfusimotoriystem—would act to reduce EMG activity to close to minimum baseline levels irrespective ofthe vertical dimension and prior jaw motion by inhibiting the overriding effects of gamma motor neurons on MERP.

423

The International Journal of Proslfiodontics

Masseler EMC on Opening and Closing with Biofeedback

References

23.

Michelotti A, Farella M, Vollaro S, Martina R. Mandibular rest position and electrical activity of the masticatory muscles. |

1.

Prostbet Dent 1997;73:4B-53.

DidbinCH, Criffitiis M|. Observation on tbe resting posture of the mandible using telemetry, in: Anderson DJ, Mathews B (eds). Mastication. Bristol: lohn Wright, 1976:100-104.

24.

6:621-628.

2.

Van Blarcom CW (ed). Theglossary of prosthodontic teims, ed 7. ) Prostbet Dent 1999:B1:39-110.

3. Watkinson AC. Tbe mandibular rest position and electromyographyâ&#x20AC;&#x201D;A review. J Oral Rehabil 1987:14:209-214.

4.

5.

6.

7.

8.

9.

10.

11.

12.

George JP, BooneMD. A clinical study of rest position using tbe kinesiograpb and myomonitor. | Prosthet Dent 1979:41:456-452.

16.

Manns A, Zuazola RV, Sirhan R, Quiroz M, Rocabado M. Relationsbip between the tonic elevator activity and tbe vertical dimension during the states of vigilance and hypnosis. | Craniomandib Pract 1990:3:1 63-170.

17.

Van Mens P, de Vries H. liitefocdusal distance determined by electromyograpbic biofeedback compared with conventional methods | Prostbet Dent 1984:52:443-446.

13.

Cross MD, Ormianor Z. Preliminary study on the effect of occlusal vertical dimension increase on mandibular postural rcsl position. Intl Prosthodont 1994:7:216-226.

21.

22.

endings to dynamic gamma stimulation in cat soleus spindles [proceedings!. I Physiol 1983:345:101.

23.

Emonet-Denand F, Hunt CC. Influence of stretcb on the persistence of dynamic fusimotor after effects [proceedings]. J Physiol 1984;353:38.

29.

Funakosbi M, Nakasbima M, Noda K, Gale E. Effects of biofeedback training on tonic masticatory neck reflex: A case report. J Oral Rehabil 1984:11:273-275.

30.

Morgan DL, Prochazka A, Proske U. The after effects of stretch and fusimotor stimulation on tberesponsesofendingsof cat muscle spindles. | Physiol I9B4;356:465--177.

31.

Proske tJ, Morgan DL. After effects of streich on the responses ofcatsoieus muscle spindles to fusi motor stimulation, ixp Brairi Res 1985:59:166-170.

32.

Taylor A. Proprioception in the strategy of jaw movement control, in: Kawamura Y, Dubner R (eds). Oral-Facial Sensory and Motor Functions. Tokyo; Quintessence, 1981:161-173.

33.

Yemm R. neurophysiological studies of temporomandibular dysfunction. Oral Sei Rev 1976;7:31-53.

34.

Yemm R. The role of tissue elasticity in the control of mandibular resting posture. In: Anderson D|, Matbews B |eds|.

Mastication. Bristol: Jobn Wright, 1976:81-89.

35.

Budyzinsky T, Stoyva |. An electromyograpbic feedback technique for teacbing voluntary relaxation of the masseter muscle. |DentResi972;52:n6-]19.

36.

Kawamura Y, FujimotoJ. Some physiological considerations or measuring rest position of tbe mandible. Med | Osaka tJniv 1957:3:247-255.

37.

Miller AJ. Electromyograpby and TMJ. In: McNeillC led). Current Controversies in Temporomandibular Disorders. Chicago: Quintessence, 1992:118-129.

38.

Burdette BH, Cale EN. The effects of treatment on masticatory muscle activity and mandibular posture in myofascial paindysfunction patients. I Dent Res 1986;67:1,126-1,130.

39.

Gervais RO, Fitzsimmons GW, Thomas NR. Masseter and temporalis electromyograpbic activity in asymptomatic, subcliriical and temporomandibular joint dysfunction patients. ] Craniomandib Pract 1989:7:52-57.

Ormianer Z, Gross MD. A 2-year follow-up of mandibular posture following an increase in occlusal vertical dimension beyond the clinical rest position with fixed restorations. J Oral Rebabil 1998;25:877-B83.

40.

Claros AC, McGlynn D, Kapel L. Sensitivitj' s|jecificit>' and predictive value. | Craniomandib Pract 1939;7:190-193.

41.

Ferrario VF, Sforza S, Miani A |r. D'Addona A, Barbibi E. Electromyographic activity of buman masticatory muscles in nor-

Perry HT Jr. Implications of myograpbicresearcb. Angle Orthod 1956,25:179-188.

Jarabak |L. An electromyograpbic analysis of muscular bebaviour in mandibular movements from rest position. | Prosthet Dent 1957:7:682-710.

mal young people. Stafisticalevaluationof reference values for ciinicai application. | Oral Rebabil 1993;20:271-280.

42.

Paesani DA, Tallents R, Murpby WC, Hatala MP, Proskin HM. Evaluation of tbe reproducibility of rest activity of the anterior tem-

Storey AT. Pbysiology of a changing vertical dimension. J Prosthet Dent 1962:12:912-921.

The Intcmaionai ]oumal of Prosthodontits

Emonet-Denand F, Hunt CC, Laporlc V. Persistent effects of fusimotor activity and muscle stretch on responses of primary

Watkinson AC. Biofeedback and tbe mandibular rest position. |Dent1987;15:16-22.

Manns A, Mirai les R, Cuerrero F. The changes in electrical activity of the postural musclesof tbe mandible upon varying tbe vertical dimension. | Prostbet Dent 1981:45:433-445.

15.

Vemm R, Berry D. On passive control in mandibular rest position. | Prosthet Dent 1969;22;30-39.

27.

Van Sickles ]E, Rugh JD, Cbu CW. Electromyograpbic relaxed mandibular position in long faced subjects. | Prostbet Dent 1935:54:570-591.

Plesb O, McCall WD Jr, Cross A. Tbe effect of prior jaw position on the plolofelectromyograpliic amplitude versus jaw position. J Proslbet Dem 1986:60:369-373.

20.

10 conventional metbods. I Prosthei Dent 1973;40:216-219.

26.

Peterson TM, Rugb JD, Mciver |E. Mandibular rest position in subjects with higb and low mandibular plane angles. Am | Orthod 1933:33:318-320.

14.

Feldmar S, Leupold RJ, Staling LM. Rest vertical dimension determined by electromyogiapby witb biofeedback as compared

RughlD, Drago CJ. Vertical dimension: Astudy of clinical rest position and jaw muscle activity. | Piosthet Dent 1981,45.

670-675.

WessbergGA, Epker BN, Elliot AC. Comparison of mandibular rest positions induced by phonetics, transculaneous electrical stimulation, and masticatory electromyography. J Prosthet Dent

Majewsky RF, Cale EN. Electromyographic activity of anterior temporal area, pain patients and non-pain patients. | Dent Res 1984;63:1,22S-1,231.

19.

25.

Garnick), Ramfjord 5P. Rest position. An electromyographic and cimical investigation.] Prosthet Dent 1962:12:895-911.

Atwood DA. A critique of research of the rest position of the mandible. | Prosthet Dent 1966:16:343-354.

MĂśller E. Evidence tbat tbe rest position is subject to servocontrol. In: Anderson D|, Mathews B (eds). Mastication. Bristol: lobn Wright, 1976:72-80.

13.

Shpiitnofi h, Shputnoff W. Astudy of physiologic rest position and centric position electromyograpby. I Prosthet Dent 1956:

poral and masseter muscles in asymptomatic and symptomatic temporomandibular subjects. I Orofac Pain 1994;8:402-406.

424

Gros5 et al

43-

44.

45.

46.

Louis I, Sheiliholslam A, Möller E, Poiiurjl activit)- in subjects with functional disorders of the chewing apparatus. ScLincI | Dent Res 1970;78;404-410.

Dohrman R|, Laskin D M . An evaluation of electrcmyographic biofeedback in the treatment of myofascial pa in-dysfunction syndname, I Am Dent Assoc 1978:96:656-662.

50.

Konchak PA, Thomas NR, Ldnigan DT, Devon RM. Freeway space measurement using mandibular kinesiograph and FMG beforeand after TENS. Angle Ürlhod1988;5e:343-350.

51.

Husley HE. The mechanism of muscular contraction. Science 1969;164n,356-1,365.

52.

Manns A, Miralles R, Palai^i C. EMC bite force and elongation of fhe masseter muscle under isometric voluntary contractions and variations of vertical dimension. | Prosthet Dent 1979,42:674-682.

Boos RH. Intermaxillary relation established by biting power. J Am Denf Assoc 1940,27:1,192-1,201.

Boyd CH, Slagle WF, MacBoyd C, Bryani RW, Wiygul ¡P. The effect of head position on electromyographic evaluations of representative mandibular p o s i t i o n i n g muscle groups. I Craniom.indib Pracl 1967,-5:5I-53.

Lund IP, Widmer CC. An evaluation of the use oí surface electromyography in the diagnosis, documentation and treatment of dental patients. J Craniomandib Disord Facial Oral Pain 1989; 3:125-137.

47.

Mohl N, Lund |P, Widmer CC, McCall W D . Devices for fhe diagnosis and treatment of temporomandibular disorders. Part II. Elettromyography and sonography. | Prosthet Dent 1990:63: 332-336.

48.

AhvoodDA.Acephalometric Study of the clinical rest position of the mandible. Part I. The variability of the clinical rest position following the removal of occlusal contacts.) Prosthei Dent 1956;6:504-S19.

49.

Mo55eterEMC on Opening and Closing wilh lîioleedback

53.

54.

55.

56.

57.

58.

Swerdlow H. Roentgencephalometric study of uertical dimension changes in immediate denture patients. I Prosthet Dent 1964; 14:635-650.

Garrett F, Angelone L, Allen Wl.Theeffect of bite opening, bite pressure and malocclusion on the elecfrical response of the masseter muscle. Am | Orthod 1964;50:435-444, Manns A, Spreng M. EMC amplitude and frequency at di fièrent muscular elongations under constant masficatoiy force or EMG activity. Acta Physiol Lai Am 1977;27:259-271.

GelbM. Length tension relationsofthe masticatory elevator muscles. | Craniomandib Pract 1990;8:139-152.

MacKenna BR, Turker KS. law separation and maximum incising force. ] Proslhef Dent19fl.3;49:726-730.

Lindauer SI, Cay T, Rendell |. Electromyographic-force characteristics in fhe assessment of oral function. ] Dent Res 199i;70: 1,417-1,421.

Literature Abstracts-

Analysts of 356 pterygomaxillary implants iti edentulous arches for fixed prosthesis anchorage.

This follow-up study included all patients with Brànemark system implants (Mobel Biocare) in a private clinic. A total ot 1,817 implants was placed in the maxillae of 169 patients. Of the implants, 356 were placed in pterygomaxillary sites; 16 different types of implant were used in this region, most of tbem 15 mm long. The cumulative survival rate ot implants in ftie pterygomaxillary area was B8.2% atter a mean functional period of 4 68 years. There were 41 failed implants at stage 2 surgery, and one implant was lost following loading. No obvious ditference in survival was found between tbe different implant types. It was concluded tbat the survival rate ot ptaryg o maxillary implants compares favorably with implants used in ofher areas of tbe maxilla. Pterygomaxillary implants provide posterior bone support without sinus augmentation or supplemental grafting.

Balslii TJ, Wolfinger GJ, Balshi SF. IntJ Oral Ma/iliofac Implants 1999; 14.398^06. References: 40.

ReprintsiDr Thomas J Balsfii. Pmsthoäonfic Intermedia, 467 Pennsylvania Avenue, # 201, Fort Wasfiington. Pennsylvania 19034—SP

Cotnparison of patients' appreciation of 5D0 complete dentures and clinical assessment of quaiityProsthodontic teaching assumes that clinical quality and patient appreciation of complete dentures are related. Some studies have corroborated this assumption while others have tailed to do so The aim of this study was to further investigate this inconclusive reiationship in an extensive material of complete denture wearers. Denture quality was assessed by a prosthodontist Patients graded their appreciation ot the dentures on a 4-point scaie. Multiple correspondence anaiysis was used for the association between patient and prosthodontist ratings. The results demonstrated close correspondence between dentist and patient appreciation of denlures when tbe dentures were rated as poor However, there was little or no correspondence for better scores ie. when Ihe dentures were rated highly. It must be remembered that all of tbe patients in this study presented for replacennent of their dentures. Tbe authors emphasized that the findings may not be relevant to new complete dentures.

Fenlon MR Sherriff M Waller JD- EurJ Prosthodont Restorative Demi9B9;7:11-14. ReferencEs: 13 R e i r c i r M i X e , R. Fenlon, Department at Pro.ff.od.ntic D.nfisfn/. Fio.r 20, G . / . Dental Ho.pifal, LondonSEI9RT. UK—/IW

_yolumel3. Number 5, 1199

425

The Inforn^tiunai lujrnal of ProsfliodunticB

Prosthodontic Decision Making Among General Dentists in Sweden. I: The Choice Between Crown Therapy and Filling

iViats Kronström, LDS' Sigvard Palmqvist, LDS, Odon Björn Söderfeldt, PhD, DrMedSc^

Purpose; The purpose of this ;tudy was to anaiyze dentists' evaluations of factors related to the choice between crown therapy and filling and to possibiy explain this by social and demographic attributes, job situation, and dentists' attitudes. Materials and Methods: Questionnaire? were sent to a random sampie of 2,059 Swedish dentists. The response rate was 76%. In the questionnaire the choice between crown therapy and filling in a clinicai situation was presented. The dentists were asked to mark their assessments of the relative importance of the different items on 14-item visual anaiogue scaies (VAS).

Multiple regressions were run tor ail 14 items. Results; Large individual variations were seen among the dentists regarding the stated importance of the various items. The items rated as the most important were "patient's wisii" and "treatment prognosis," and the items rated as least important were "treatment time required" and "number of visits required for treatment." The differences between groups were small, and for no item exceeded 0.7 slep on the 8-grade VAS scaie. No data reduction was possible using principal components analysis. Conclusion: Tiie study showed great variations among individual dentists. The dentist-reiated factors explained iittie of the variance. The results indicated that [he questionnaire instrument did not fully capture the real influences on the treatment choice between a filling and an artificial crown. IntJ Prosthodont

1999; 12:42 6-431.

D

ecision making in prosthodontics involves complex interactions of possible decisions.^"^ It is wideiy acl<nowiedged that when confronted with the same clinical situation there are variations among dentists regarding the choice of treatment when intervention is indicated. The reasons for these variations and what factors influence the decisions are, however, not well known. Some reports have focused on the great variation in dentists' assessments of ciinicai

'Senior Consultant. Department oí Prosthetic Dentistry. Centrai Hospitai, Skövde: and Department of Prosthetic Dentistry, Maimö University. Sweden.

"Professor. Departmen! of Prosthetic Dentistry. University of Copenhagen. Denmari<; and Department oí Prosthetic Dentistry.

Maimö University, Sweden.

'Proíeísor and Chair, Department oí Orai Public i-leailh, Maimö Universily, Sweden.

Reprint tequestsi Dr Mats Kronström, Department of Prostiietic Dentistry, Centrai Hospitai. S-S41 85 Skovde, Sweden. Fax: + 46500 43 29 30. e-maii: n<ati.kronstrom'?'ltsi<ar.se

The Iniematioiial lournal of Proslliorioiilici

426

conditions and selection and type of restorative treatment.^"^ ' Other studies have shown wide differences in diagnosing caries even among experienced examiners, and great variation in restorative service rates and management of periapical lesions in endodontically treated teetb.'^"'^ Although dental education is based on scientific and clinical experience the high range of variability in decision making indicates strong individual preferences among the dentists.''

Decision making in dentistry is a complex process including both dentist- and patient-related factors.^^'^° It has been reported that fear of accusation of malpractice, years in profession, and the perceived patient need play important roles.^' In one study the choice between crown therapy and fiiling, and aiso between fixed and removable partial dentures, was investigated. The result showed that the participating dentists ranked "technical factors" as more important than "patient factors." Only A ' of the dentists ranked the cost of treatment to be important in choosing between the therapies for the 2 situations. Patient preference was

Voijme 12, Nun-l-sr s \<><)<i

Krönst rom et al

Prosthodonlic Decision Making Among Swedish Geneml Dentists

ranked to be even less important. The results indicated that patients may have limited influence on the treatment prescribed.-' In research on decision making a fundamental distinction can be made between empirical and normative theories. Empirical theories try to understand the continuous process in actual decisions, while normative theories try to find a way to optimize decisions, ie, how decisions should he made. There are few theories on empirical decision making, while there is an abundance of normative theories.'- However, normative theories lack relevance in the present context.

The objective here is to contribute to the empirical understanding of actual decisions, not to obtain knowledge about which decisions should be made. Among empirical theories, Brunswik's lens theory implies thatonly a few key factors play a decisive role in clinical decisions—these are "cues" for clinical behavior.'^ In dentistry this theory seems to have interested radiologists in particular.-"* As a preparation for the present study a pilot study that showed great differences among individuai dentists regarding the importance of various factors for the choice between treatment options was performed in 1995.-^ This initiated the present nation-wide questionnaire study on prosthodontic decision making among Swedish general dentists. Considerable variation in practice profiles and attitudes was seen among individual dentists and between the genders, as well as among dentists in the 2 Swedish delivery systems, private practice (PP) and the Public Dental Health Service (PDHS).^^-" The present article addresses the choice between crown therapy and filling. Indeed, this decision situation could be difficult for the dentist with respect to patient costs and the introduction of new restorative materials. The development of new dental composites in combination with improved bonding techniques now offer an alternative to crown therapy in the restoration of severe tooth lesions. This may aiso make the choice more difficult between filling and crown therapy wben taking factors such as longevity of restorations, patient costs, and esthetic outcome into consideration. There is, however, no "gold standard."

In the present study Swedish general dentists were asked to evaluate the importance of various patientrelated items in the choice between crown therapy and filling in a case presented with a fractured cusp on a maxiiiary premolar. The aim was f7)to describe how dentists evaluated the importance of various items related to the treatment situation and (2) to determine whether the differences among dentists in these evaluations could be explained by dentistrelated factors, social and demographic attributes, job situation, and attitudes.

Materials and Methods Questionnaires were sent to a random sample of 2,100 general dentists in Sweden. The sample was collected from the membership register of the Swedish Dental Association. The selection of subjects has been presented elsewhere.-^ A total of 1,608 dentists responded. Among them, 41 reported that they were no longer practicing as general denlists and were therefore excluded from the sampling frame, rendering a sample size of 2,059 individuals. The remaining number of responding dentists was 1,567, yieidinga response rate of 767o. Ofthe participating dentists, 50% were PP dentists and 50% were PDHS dentists. Among the participants, 42% were female and 58% were male. The mean age in the study population was 46.3 years. Analysis of the nonresponse regarding age, gender, and delivery system was performed and presented elsewhere.-^' In the questionnaire the following clinical situation was presented: "You are to choose between crown therapy or filling (amalgam/composite) for the treatment of a fractured cusp on a premolar in the maxilla. How do you assess the following items?" The items were preceded by a general instruction: Amethod to find out treatment profiles among dentists is to start from actual ciinicai situations. One asks the dentist to judge whal importance he or she gives to different factors in their own choices. There is no right or wrong and we have tried to select such situations where one really can have different opinions. We ask for your own assessment of each single item weighted to the other ones. Stale your opinion regarding the relative importance of the different factors with an x on the scale, where the distance to the end-points should mirror the relative importance you want to give the item.

The items to consider were: (1) patient age, ¡2) patient's general health, ¡3) patient's wish, (4) amount of remaining tooth substance, (5)technicai difficulty of therapy, (6) prognosis for delivered treatment, (7) marginal bone level, (8) pulp status—root-filled or vital tooth, 19) poor oral hygiene—gingivitis, (Wl your own experience of crown therapy, ( I J^reatment time required, (12) number of visits required for treatment, (13) cost for patient, and (14) esthetic outcome. The visual analogue scale (VAS) responses were coded in 8 equidistant steps ranging from "unimportant" (1) to "decisively important" (8).

Explanatory variables were constructed from a series of items in the questionnaire categorized as "social and demographic attributes," "job situation," and "attitudes of dentist." The social and demographic attributes included the foiiowing items: the dentist's age (in 9 categories: < 25, 25-29, 30-34, 35-39, 40-44, 45-49, 50-54, 55-59, and 60 years and

427

The tntemslionai |ou/nal of Prostli odontic s

Kronsiröm el al

Prosltiodonfic Decision Making Among Swedish Ceneriil Denlisis

•

above); gender (male or female); dental school (Umeâ, Stockholm, Göteborg, or Malmö—the firsi 3 were used as dummy variables in the analyses with "Malmö" as the reference category); delivery system (PP or PDHS); years in profession (any figure could be given); and size of community where practicing ¡a Liken scale with 6 categories ranging from "small village < 5,000 inhabitants" to "one of three big cities > 200,000 inhabitants").

A series of questions was included to capture the dentists' job situation: •

•

•

•

•

•

•

Finally, 3 factors regarding dentists' attitudes were included. The factors were obtained from factor analysis of 10 attitudinal statements and are presented elsewhere.-^ The 3 factors were labeled "delegation," "patient information," and "patient influence."

Statistical Methods

"On average, what percentage of your clinical time do you use for dental care of adults?" (Any percentage could be given.) The variable "weekly working hours used for dental care of adults" was calculated by multiplying the percentage figure by the reported weekly working hours, using class means in the categoric responses.

"Weekly working hours used for prosthodontics."

(Any figure could be given.I The variable was calculated by multiplying the reported percentage figure for clinical time used for prosthodontics by reported working hours, using class means in the categoric responses, "How often do you discuss differenttreatment options with a colleague?" (A Likert scale with 6 categories ranging from "at most once a monlh" to "many times a day.")

"How do you assess the demand for services at your clinic?" (A Likert scale with 4 categories ranging from "lack of patients" to "great demands—patients queuing.")

"Howwould you describethe majority of your patients?" (A Likert scale with 5 categories ranging from "mostly routine services" to "large need and demand for treatment.")

"Concerning opportunities for postgraduate courses, what are you primarily interested in?"

(Eleven options were given: cariology, oral surgery, endodontics, prosthodontics, periodontics, community dentistry, pédiatrie dentistry, orthodontics, temporomandibuiar disorders, dental materials, and oral radiology—in the analysis those interested in prosthodontics were coded as 1 and the others were 0.)

"Why did you choose the dental profession?" (Six options were given: to help people, to do a technically advanced job, to get a well-paying and secure job, because the profession has high social slatus, because the profession has an element of creativity, and to get a varied and interesting job.

This variable was included as a dummy variable with the first alternative, "to help people," as the reference category.)

The Internaiionai lourrai nf Prosthodonlics

"How satisfied are you with your work as a dentist?" (A Likert scale with 5 categories ranging from "dislike it" to "like it very much.")

428

The data were first analyzed in frequency tables with means and standard deviations calculated for the entire sample. Differences in means for delivery system and gender were tested with the ¡test. The items were all subjected to factor analysis using principal components analysis (PGA).^^ The Kaiser criteria and inspection of scree plots was used for choice of the number offactors. Multiple regression analyses were run on the 14 items in the questionnaire as dependent variables using social and demographic attributes, job situation, and attitudes as independent variables. Residual plots were inspected for detection of heteroscedasticity (unequal distribution of errors along the regression line).^^

Results There were great variations for several factors as indicated by the generally large standard deviations and ranges of the VAS val ues (Table 1 ). The items given the highest importance were "patient's wish" (no. 3) and "treatment prognosis" (no. 6), which also showed the lowest standard deviations. Tbe items given the lowest importance were "treatment time required" (no. 111 and "number of visits required for treatment" (no. 12).

When analyzing the items bivariately several ofthe distributions differed with respect to delivery system and gender. However, the differences between groups were small. The largest difference (mean 0.7) was seen for female versus male dentists concerning assessment ofthe importance ofthe patient's general health, where female dentists gave that factor greater importance.

When analyzing the factors using PCA 5 factors were found in the first run with a total variance explanation of 60.5'/o. The solution was tested by dividing the sample into 2 equal randomly selected parts and comparing the results. With a stable factor solution the result should be the same in the 2 samples. This was not the case; half of the sample gave a different item pattern compared to the other half. The solution was regarded as un interpretable. Therefore, no data reduction was considered possible.

Multiple regression analysis was performed for each of the 14 items as dependent variables (Table 2). The

• 12, Numbers, 1099

Pros tho clon tic Decision Making Among Swedish General Dentists

Krön ström etal

Table 1 Means and Standard Deviations (SD) for Treatment-Related Factors and Differences Between Means witin Respect to Delivery System and Gender* Item 1.

2.

3.

4.

5.

6.

7.

8 9.

10.

11.

12.

13.

14.

SD Patient age Patient's general health Patient's wish Amount of remaining tooth substance Technical dtfficulty of therapy Prognosis for delivered treatment Marginal bone level Pulp status—root-fjiied or vital tooth Poor oral hygiene—gingivitis Your own experience of crown fherapy Treatment time required No. of visits required tor treatment Cost for patient 'flHM Esthetic outcome

3.6 4.8 7.1 6.5 3.9 7.0 5.9 4.6 5.2 5.1 2.5 2.5

^mm 6.2

2.1 2.0 1.1

1 6 2.3

Mean difference (PP/PDHS¡

Mean difference (male/female)

-0.3 -0 4 -0.2 -0.1 -0.5

1.1 1.7 2.3 1.9 22 1.8 1.7

00 0.2 -01

1.3

0.0

0.004 0.000 0.000 0.351 0.000 0.654 0.009 0.317 0.065 0.000 0.000 0.000 0.000 0.792

-0.2 0.5 -0.5 -0.4 -0.4

-0.6 -0.7 -0.1 -0 3 -0.5

0.000 0.000 0.077 0.000 0.000 0 252 0.008 0 003 0.002 0.000 0.015 0.155 0-080 0.015

-01

-0.2 -0.3 -0.3 0.5

-0.2 -0.1 -0.2 -0.2

-1557snÊi563sampie

Table 2 Multiple Regression Model Regarding Assessments of Importance for the Variables Influencing Dentists' Choice of Treatment' Dependent variable^ Independent variable Social and demographic attributes Age -0.24 -0.30 -0.52 -0.49 Gender , -0.05, Years in profession -0.04 Size of community where practicing Dental education -0.22 Stockholm -0.34 Göteborg Job situation Treatment discussion with colleagues (6 categories] Jotj satisfaction (5 categories) Weekly vicrking hours used for dental care ot adults Weekly wori<ing hours used for prosthodontics Reason ¡or choosing dentistry -0.28 -0.22 Secure job and good income -0.52 0.49 Social status Varied job -0.08 Treatment comprehensiveness Want course in prosthodontics Attitudes of dentist Delegation 0.01 -0.003 0.01 0.01 Patient information 0.003 Patient influence Adjusted r square Model significance, P

0.41

0.48

-0.10 -0.11 -0.14

O.ÍM"

-0.04

0 03

-0.21 -0.43 0.24 -Ü.21 0.13 0.01 0.01

-0.16 0.17 0.005 0.005-0.01 0.005

0 04 0 05 0 03 0 02 0.04 0.003 0.02 0.01 0.04 0.02 0.02 0.02 0.03 0.03 0:000 0:000 COOO 0.000 0.236 0.002 0.012 0.000 0.001 0.000 0.000 0.000 0.000

•Only signilicant independent variables and coeflicients (PS 0.05) are stated.

'See Table 1. n = 1455.

bivariately signilicant differences between PPs and PDHS dentists were not significant in any of the multivariate analyses. For gender, however, the differences remained significant in some models. The

adjusted r squares, indicating percent explained variance, were low for all models, never exceeding 0.05.

There was thus a low precision in the models. Most ofthe independent variables were not significant. The

.0/olumet2. Numbers, 1999

429

The irternational lournal of Prostiiodontici

Prosfhodontic Decision Mailing AmonR Swedish General Dentists

attitude variables showed significance in several models. Heteroscedasticity was obvious for items 3, 4, 6, 11, 12, and 14, which means that the coefficient estimates could have inflated significance estimates.

For interpretation of Table 2 one should keep in mind the nalure of the regression coefficients. The magnitude of the coefficients depends on the units of botin the independent and dependent variables. For example, the gender difference for the items "patient age" and "patient's general health" means 0.5 units less importance on the 8-grade VAS scale for female compared to male dentists. The values for the attitude to "patient information" in the model mean that for each unit in the 100-grade scale of the attitude there is an increase in the importance ofthe respective item of 0.01 units on the 8-grade scale. The attitude effect is thus as large as the gender effect when the attitude reaches 50 units on the attitude scale (0.01 x 50).

Discussion Themain resu Its nfthe present study were: fíMhereare great individual variations in evaluating the importance of various patient-related factors for choosing between a filling and an artificial crown; (2) no data reduction was possible using PCA; and f^J dentist-related factors {social and demographic attributes, job situation, and attitudes] explained very few ofthe variations.

The present results indicating tbat general dentists in Sweden regard "patient's wish" and "treatment prognosis" as the most important items are contradictory to results from a similar US study in which American dentists ranked technical factors (extent of tooth damage and periodontal status) as the most important ones.'^ In the US study senior dental students also participated. A significantly lower percentage of the students ranked these technical factors as important. The students gave more importance to the items "patient preference" and "oral conditions," a pattern more resembling the findings of tbe present study.

These differences between dentists in Sweden and in the United States might be a result of a more authoritarian style for dentists in the United States. It may also be a result of a time factor—the American study was performed about 10 years ago, and the importance of patient influence has increased over time in modern dentistry. The different types of delivery systems in the United States and Sweden (in Sweden only 50% of the dentists are PPs] might influence the profiles of dentistry in the 2 countries. By law, the PDHS in Sweden provides for dental care of children and adolescents up to the age of 20, after which the patient has to decide either to continue as a regular patient in the PDFHS or to attend a private dental clinic. This might create a situation in which tbe patient's influence is

The International ] •

I ol ProBfhodontics

430

increased because of the competitive situation between the 2 delivery systems even though tbe fees are the same. By tradition a more preventive profile has characterized the care in the PDHS, while a more restorative one has dominated in private practice.^^'^' These differences are, however, less obvious today.

It was not possible to reduce the 14 items of the decision situation into a few factors in PCA. This further underlines the complexity of clinical decision making in prosthodontics and gives no support for the lens theory in this context. According to tbe lens theory for decision making only a few basic factors affect actual decisions.^' In the present study it was not possible to obtain an interpretable and stable data reduction to only a few factors. Tbis result is underlined by the fact that in the pilot study a different number of factors was obtained although tbe model was stable in that study,^'' Another reason could be a lack of realistic reflection of actual decisions in tbe methodology used here, with too little information given about the treatment situation.

Compared to the considerable individual differences in opinion the differences between groups of dentists were smaller. The bivariate differences between male and female dentists as well as tbose between PPs and PDHS dentists were for most items statistically significant Multlvariately the differences remained statistically significant between the genders for several items but disappeared for the delivery systems.

This probably mirrors the differences in age and gender between the 2 systems. Tbe same pattern was seen in a previous study regarding dent ist-related factors influencing the amount of prostbodontic treatment (Kronstrom M, et al, unpublished data]. The result also supports findings from fields outside dentistry that organizations have little influence on decisions made by individuals.•'Tbere were great variations in evaluations among individual dentists. Other studies also confirm the observations of large individual variations among den(¡5^5 16,19 Hypothetically the size of the standard deviations migbt be because ofthe possibility that some of the participants used tbe wbole scale wbile others only used the central part of it. However, tbis explanation is contradicted by the large variation in mean values, ranging from 2.51 to 7.07. An interesting finding was tbat the mean values and standard deviations for most items showed a striking resemblance to tbose from the pilot study.^^ This gives support for the reliability and validity of the results, yet the dentist-related factorsexplained very little of the variance. Apparently we have not been able to capture all factors that influence the treatment choice befween a filling and an artificial crown. This is an argument for the idea that decision making in dentistry isa multifactorial process probably with great individual variations.

Volume 13, Numbers. 1999

Prosthodontic Decision Making Amons Swedisii General Dsntisls

In dentistry, as compared to medicine, a wider

11.

Rytomaa I, ISrvinen V, lärvinen J. Variation in caries recording and restorative treatment plan among university teachers.

Community Dent Oral Epidemiol I979;7;335-339.

12.

Milenian P, Purdell-Lewis D, van der Weele L. Effect of variation in caries diagnosis and degree of caries on treatment decisions by dental teachers jsing bitewing radiographs. Community Dent Oral Epidemiol 1983,11:356-362.

13.

Mileman P, Purdell-Lewis D, van der Weele L. Variation in radiographie caries diagnosis and treatment decisions among university teachers. Community Dent Oral Epidemiol 1983;! 0:329-3 34.

14.

Espelid I, Tveit A, Haugefjord O, Riordan P]. Variation in radiographie interpretation and restorative treatment dec is i ojis on approximal caries among denlists in Norway. Community DenL Oral Epidemiol 1985,-13:26-29

range of different treatment options are suggested to be available for the same clinical situation.-o This of course makes the decision process more compiex and influenced by factors of which we have iittie knowiedge, such as "dentist's personality" and "practice characteristics."15 To get a better understanding of the factors involved in clinical decision making, performing personality tests could be considered.

Attitudes had a significant influence in some of the regression models, but attitudes mirror such personai traits only to a limited extent.

1 5.

The clinical situation in the questionnaire was deliberately not too detailed, as this might have guided thedentistsin their assessment of the various factors.

The great standard deviations for most items confirmed that there realiy was a choice. Nevertheiess, further studies are necessary to investigate other factors of importance in decision making in prostbodontics. An important further issue is therefore to develop an instrumentto capture some of these factors.

The present study has demonstrated that decision making concerning the choice between fiiling and crown therapy is very multidimensional. No single factor or decisionai dimension could be discerned for this choice. In our opinion this reflects the complexity of even such a relatively common ciinicai decision.

Acknowledgments This study was supported by grants from the Swedish Council for Sociai Research (pra)ect no. 94-0068; 3B], and from the Public Health Institute in Siiaraborg County.

References 1.

i<ay E, Nuttall N. Clinicai decision making—An art or a science?

Parti.BrDentl1995;25:76-7a.

2.

Kay E, Nuttall N. Clinical decision mai(ing—An art or a science?

Part III. Br Denl | 1995;25:153-1 55.

McCreeryA.TrueloveE. Decision making in dentistry. Part I: A historical and methodological overview. J Prosthel Dent 199I;65:447-^51.

3.

4.

5.

McCreery A, Truelove E. Decision making in dentistry. Pan Ii: Clinical applications of decision melhods. | Prosthel Dem 1991;65:575-585.

Dodson TB. Evidence-based medicine. Its role in the modem practice and teaching of dentistry. Oral Surg Oral Med Oral Pathol Oral Radiol Endod l997;83:192-!97.

6.

Elderton R|, Nuttall NM. Variation among dentists in planning treatment. Br Dent J 1983;154:Z0I-206.

7.

Nuttall NM, Elderton RJ. The nature of restorative dental treatment decisions. Br Denl 1 1983;154:363-365.

Bader JD, Shugars DA. Agreement among dentists' recommendation for restorative treaiment.l Dent Res 1993:72:891-8%.

BaderjD, Shugars DA. Understanding dentists'restorative treat-

8.

9.

ment decisions. J Public Health Dpnt 1992;52:102-n0.

10.

Crembowski D, Miigrom P, Fi^et L. Variation in dentist service raies in a homogeneous patient population. J Public Health Dent 199O;50:235-243.

1 6 Crembowski D, Miigrom P, Fiset L. Dental decision making and variation in dentist service rates. Soc Sei Med 1991 ;32:287-294.

17. KvistT, Reit CEsposiloM, Mileman P,BianchiS,PetterssonK, Andersson C. Prescribing endodontic retreatment: Towards a theory of dentist behaviour. Int Endod J1994 ;27:285-29O. 18. Reite, Grondahi H-C. Management of periapical iesions in endodontically irealed teeth. Swed Denl J 19ö4;8:1-7.

19. Crembowski D, Miigrom P, Eiset L. Ciinicai decision making among dental students and gênerai practitioners. I Denl Educ 1989;53:189-192.

20. Ettinger R. Clinical decision making in the dental treatmcnl of theelderiy. Ceiodontology 1984;3:157-¡65.

21. Grembowski D, Miigrom P, Fiset L. Factors mfiuencing dental decision making, i Public Health Dent 1988;4a:l 59-157.

22. Brehmer B. The psychology of linear judgment models. Acta Psychol 1994;87:737-154 23. Wighton RS Use of linear models iti analyîe physician's decision. Med Decision Making 1988;8:241-252.

24. Knutsson K, Brehmer B, Lyseii L, Rohiin M. General dental practitioners' evaluation of the need for extraction of asymptomatic mandibuiartliird moiars. Community Dent Orai Epidemiol 1992; 20:347-350.

25. Söderfeldt B, Palmqvist S, Eriksson T, Kronström M, Carlsson C£.

A questionnaire instrumentto assess ciinicai decision making in prosthodontics among gênerai praclitioners. Acta Odontol Scand 1996;54:314-319.

26. Kronström M, Palmqvist S, Eriksson T, Soderfeldt B, Carlsson GE. Practice profile differences among Swedish dentists. A questionnaire study with special reference to prosthodontics. Acta Odontol 5candl997;55:265-269.

27. Kronström M, Palmqvist S, Söderfeldt B, Carlsson GE. General dentists' attitudes toward delegation, information, and patient influence in a proslhodontic context. IntJ Prosthodont 1999;12:45-50.

28. Kim J-0, Mueller CW. Factor Analysis. Statistical Methods and Practical Issues. Beverly Hills, CA: Sage Univ Papers, 1978.

29. Achen C. Interpreting and Using Regression. Beverly Hills, CA: Sage Univ Papers, 1983.

30. Sundberg H, l.indblom C, Randver L. Vuxenvârden i Kalmar iän âr 1991. Tandiakanidningen 1993;85:236-24S. 31. Sundberg H, Owaii B. Eörsakringslandvarden under aren I974-l981.Tandlakartidningen I984;76:837-84a.

32. Söderfeidt B, Söderfeldl M, Jones K, O'Campo P, Mutanei C, Warg L-E, Ohison C-G. Does organization matterí A muitilevel anaiysis of demand, control, and psychological health in human services. Soc Sei Med 1996;44:527-534.

Drake CW, Maryniuk CA, Bentley C. Reasons for restoration replacement: Differences in practice patterns. Quintessence Int 199O;21:125-l.3O.

12, Njmber 5,1

431

The Inrernalionaf Journal of Proslhodontics

Two-Body Wear Resistance and Degree of Conversion of Laboratory-Processed Composite Materials

Lisa A. Ronald Robert iUeade

Knohloch, DDS, Mff E. Kcrhy, DMD^ Seghi, DDS, MS'' van Putten, DDS, MS''

Purpose: Tlie purpose of this investigation was lo evaluate the relative 2-body abrasive wear and degree of conversion of 4 laboratory-procès sed composites (Targis, Concept, belleGlflss, and Artglass) and 2 direct placement composites (Herculite and Heliomolar) after 7 days of storage. Materials and Methods: Human enamel was used as a positive control for 2-body abrasive wear, and 10 cylindric specimens (3.5-mm diameter, 8-mm height) of each material were prepared and stored in distilled water at 37 ± 2°C (or wear testing. Relative 2-body abrasive wear rates were determined using a 30-|jm diamond disk and a 2-body pin-on-disk apparatus. Subsequently, 3 polymerized specimens that had been stored in sealed polyethyienc vials for 7 days were prepared for degree of conversion testing. The degree o( conversion was determined on an infrared spectrometer using standard baseline techniques and various internal standards. Results: Statistical analysis using analysis of variance and the Tukey-Kramer multiple range test indicated significant di((erences between several of the materials tested for both 2-body abrasive wear and degree of conversion. Conclusion: Concept exhibited significantiy less 2-body abrasive wear compared to the direct and indirect composites IP< 0.01). Concept and belleGlass exhibited a mean degree of conversion that was significantly higher than any oftheothercomposites tested (P< 0.01). Int I Prosthodont 1999:12:432-438.

T

shrinkage and incompiete cure still remain a problem.•'"^ To overcome some of the deficiencies of the direct-placement composites attention has been directed toward the use of laboratory-processed composites. Advantages of indirect composite restorations include superior marginal adaptation, decreased polymerization shrinkage, and a greater degree of methacrylate conversion.-"-^ Disadvantages include laboratory costs associated with fabricating the restoration and the additional chairsidetime involved in making an impression of the preparation and cementing the restoration.

he use of composite for the restoration of posterior teeth has increased over the past decade because of improvements in the mechanical properties of the material a n d patient d e m a n d for esthetic restorations.'- Despite improvements in the physical properties caused by increased filler loading and decreased filler particle size, excessive polymerization

MssJSianI Professai, Sei:tiori of Restorative Dentistry, Prosttiodontici snd Bndodontics, The Ohio Stale University Cotiege af Dsnliilry, Coiumbus, Ohio. ''Associate Professor. Section of Restorative Dentistry, Proíthodonticí and indodontics, The Ohio State University Coitege of Dentistry, Coiumhui, Oiiio,

Several new laboratory-processed composites that use curing methods aimed at increasing the degree of conversion have been introduced. These methods Reprint requests: Or Usä A. Knablach, The Ohio State University include a combination of both beat and pressure College oí Dentistry, Depgrtmenl af Restorative Dentistry, or elevated ligbt intensity to allow for secondary curProsthodontics snd Endodontics, 305 West ¡2th Avenue, Coiumbus, Ohio 43210. e-mmi: knobio<:h.3®o5u.edij ing of the composite. Composite materials that are highly polymerized have been shown to exhibit imThis paper wai presented ,it the !998 AmericEin Association for proved mechanical properties including greater wear Dentai Research Meeting, Minneapolis.

The Intcrnaiionai |ourn,ii oí Crostliodonlicí

432

Voljme 12, Nun-'

Knoll I och et al

Table 1

J-Body Wear Resistance and Conversion of Composites

Composite Materials Tested

Composite materiai (manufacturer)

Type

Composition

Targis (Ivoclar)

Indirect ccmposite

Artgiass (Kulzer)

Indirect composite

beileGlass (MicroDent)

Indirect composite

Concept (ivociar)

Indirect homogenous microfill composite

HercuiiteXRV(Kerr)

Direct microhybrid composite

Heliomolar (Ivoclar)

Direct non homo geno us microtiil composite

Polymerization method

Barium glass and mixed oxide tiliers (0.04 and 1.0 (im) in bisGMA and urethane dimethacrylate resin (tiiler 75 wt%¡ Barium aiyminosiiicate giass (0.7 \im) in öimethacryiate and muitifunctionai methacryiate resin (tiller 69 mt%) Pyrex glass tiller (0.6 |jm) in urethane and aliphatic dimetii aery late resin (tiller 74-78 wt%) Pyroiytic siiica dioxide (0.04 (jm) in urethane d i methacryiate resin (tiiler 70 wt%) Barium alumino-borosilicate and pyroiytic silica dioxide (0 6 \jm) in bisGMA-based resin (fiiler 78 wt%) Prepoiymenzed agglomerated organic filier with pyroiytic siiica dioxide (0.04 tim) in bisGMA and urethane dimethacryiate resin (tiller <: 65 wt%)

BisGMA = £,£-bis(4-(£:-hyäroxy-3-methacryloxy propoxylphenylene] propane 1.6-diamino-2.4.4-trinietliyHiexane.

intense visible iight (pulsed) for 20 ms with 80-ms dark intervals Heat (140"C) and pressure (80 psi) in nitrogen atmosphere Heat (120X) and pressure (85 psi) Direct visitjle iight Direct visibie light

ethacryiate = N.hJ-Bisp-metliacroyloxyetlioiycarbonyl)-

Two-Body Abrasive Wear

resistance, hardness, and flexural strength.''^"'" In addition to the mechanical properties the degree of conversion may also influence clinical performance in areas such as resistance to fracture, wear, and degradation at the margin."

Few independent studies are available evaluating the mechanical properties of these newly available laboratory-processed composites. The purpose of this investigation was to evaluate the relative 2-body abrasive wear and degree of conversion of 4 indirect composites and 2 direct composites. Information about the wear resistance and degree of conversion of these materials would be helpful in projecting their long-term durability in the oral environment.

Ten cylindric specimens of each resin system, measuring 3.5 mm in diameter by 8 mm in height, were prepared in glass molds. Manufacturers' specifications were followed for specimen preparation and method of cure. Direct composites were visible-light cured for a total exposure of 120 seconds. Indirect laboratory-processed composites were polymerized according to the manufacturers' instructions.

Specimens were maintained in distilled water at 37 ± 2°C for 7 days before wear testing.

The relative 2-body abrasive wear rates were then determined using a 30-\im diamond disk with a 2body pin-on-disk type apparatus. Specimens were held in contact with the abrasive surface using a continuous 1.5-N load and were rotated at a constant rate of 95 rpm while they traced a circular orbiting pattern.

The linear speed of the tracing was about 0.12 ms"' and the length of each circular stroke was approximately 75 mm. The contact surfaces were continuously flushed by flowing tap water to ensure tbat the diamond disk surface remained free of wear debris during testing. The length ofthe sample was monitored at 2-second intervals by a linear variable differential transformer (LVDT, Sony) with an accuracy of 0.0005 mm. The specimens were subjected to approximately 500 revolutions. The number of revolutions was slightly different between specimens; however, the data is normalized to the number of pm of wear per revolution. Both length and number of revolutions

Materials and Methods Four indirect laboratory-processed composites were studied: Targis (Ivoclar), a bisGMA- and urethanebased dimethacrylate composite; Artgiass (Kulzer), a dimethacrylate and multifunctional methacryiate composite; belleClass (MicroDent), a urethane-based composite; and Concept (Ivoclar), a urethane dimethacrylate-based homogenous microfill. Two direct-placement composites were also studied: Herculite (Kerr), a bisGMA-based microhybrid composite; and Heliomolar (Ivoclar), a nonhomogenous microfill composite. The polymerization methods are listed in Table 1. Human enamel was used as a positive control for abrasion. Enamel specimens were hollow-core drilled from third molarteeth.

•12 Nurrbor5, ¡999

Intense visible iigtit (320-500 nm) and tieat (208T)

433

2-Godv Wear Resistance and Conversion of Composites

Knobloch et a

Fig 1 Mean 2-body abrasive wear. Groups conneoted by a horizontal line are not significantly different (o= 0.05).

Enamei

Table 2

Concept

Heiiomoiar beiieGiass

Hercuiite

Absorption Peaks

Group

Wave No. (cm"')

Methacrylate peak C=C Reference peak Ester Aromatic,

1608

Aromatic^

1582

N-H (urethane]

3350

Artgiass

crystals, and placed into a cell holder in the specLrometer. The concentration of methacrylate carboncarbon double bonds (C=C) was then determined by obtaining a spectrum from 16 scans over a bandwidth of 850 to 4,000 cm"' at a resolution of 4 cm"'.

Polymerized specimens {n = 3) that had been stored in sealed polyethylene vials for 7 days at 37°C were cryoground under liquid nitrogen into afine powder.

Subsequently, 4 mg of resin powder were biended with 100 mg of infrared-grade potassium bromide in a specimen holder and pressed into a transparent disk using a pellet-maker kit (KBr Port-a-Press, international Crystal). The specimen holder was then transferred to the spectrometer and spectra were obtained using the same parameters as with the unpolymerized specimens. A comparison was then made between the absorption peak intensities ofthe C=C methacrylate bonds and various internal reference peaks (Table 2] before and after polymerization according to the following formulas (Abs = absorption):

Material

1640 1730

Targis

Concept Angiass belleGiass Targis Heroulite Artgiass Heiiomoiar Targis Artgiass Hercuiite Concept Heiiomoiar belleGiass

were recorded on a computer. A linear regression anaiysis was performed on all data to calculate 2-body abrasive wear. The slope ofthe regression line represents the rate of abrasion in [jm/revoiution. Specimens were gold coated and scanning electron microscopy (SEM, Edax DX4-1) was performed to examine the wear surfaces.

residual (% C=C) =

(Abs [C=Cl/Abs [ reference peak])monomer

Degree of Conversion The degree of conversion for each new resin system was determined on a Fourier Transform Infrared Spectrometer (Midac] using standard baseline techniques and various internal standards as described by Ferracane and Greener'^ and Urbanski et al.'^ Samples of the unpolymerized resin systems (n = 3) were diluted in chloroform, smeared between 2 NaCI

The internatignal loiirral of Prosthodontics

(Abs|C=C]/Abs[reference pcak])polymer

degree of conversion = 1 0 0 % - residual (% C=C) Statistical analysis using analysis of variance (ANOVA) and the Tukey-Kramer multiple range test showed significant differences between several of the composites tested for both 2-body abrasive wear {a = 0.05] and degree of conversion (OĂ? = 0.05).

434

Volume 12, Number 5, 1999

2-Body Wear Resistance and Conversion of Composites

Knoblochetal

R92 SEM view of Hercullte surface exbiDits a microstructure in which microfractures are evident. (Original magnification x 5,000; bar = 1 ^Jm.)

Fig 3 SEM view of Concept surface exhibits a microstructure relatively tree ot microfractures. (Original magnification x 5.000; bar= 1 |jm.]

Fig 4 Mean degree of conversion. Groups connected by a horizontal line are not significantly different (a =0.05].

Concept

Bel led ass

microfill composite, exhibited significantly less 2body abrasive wear when compared to Herculite, a direct microhybrid composite.

For 3 specimens from each group SEM views were evaluated- Representative SEM views are presented in Figs 2 and 3. Evidence of microcracking was noted for Herculite (Fig 2): however, microcracks were not evident for Concept (Fig -"51.

Results Two-Body Abrasive Wear Mean 2-body abrasive wear results are reported in Fig 1 (P< 0.01]. Tbe enamel control exhibited a mean 2-body abrasive wear tbat was significantly lower than any of the direct or indirect composites tested.

Concept, a laboratory-processed microfill composite, exhibited a mean 2-body abrasive wear that was significantly lower than any of the other composites tested- BelleClass, also a laboratory-processed composite, exhibited significantly less 2-body abrasive wear than Targis and Artglass. Heliomolar, a direct

. Number 5,1999

Arigl

Degree of Conversion Mean degree of conversion results are reported in Fig 4 (P< 0.01}- Concept and belleClass, 2 laboratoryprocessed composites tbat are both heat and pressure

435

The International

I of Prosihodontics

l-Budy Wear Resistance and Conversion of Composites

Knob loch et al

cured, exhibited a mean degree of conversion that was significantly higher than any of the other materials tested. No significant difference was noted between Targis, a I a bora tory-processed composite, and Heliomolar, a direct-piacement composite. Herculite exhibited a mean degree of conversion that was significantly lower ihan any of the other materiais tested.

Discussion Clinically, the process of wear is complicated and most likely involves several different mechanisms. In addition, several different definitions of these mechanisms are found throughout the literature. The fundamental mechanisms of wear described in tribology are: 2-body abrasive wear, adhesive wear, fatigue wear, fretting wear, erosive wear, and corrosive wear,"''^ Condon and Ferracane^^ described the 2 main mechanisms of wear associated with dental composites as abrasion and attrition, Soderholm and Richards" described abrasive wear as the mechanism most referred to by the dental community.

However, a distinction is made between 2- and 3body abrasive wear^': 3-body abrasive wear occurs when a freely moving abrasive medium is placed between 2 independently moving surfaces, whereas 2body abrasive wear occurs when the abrasive particles are attached to one of tbe surfaces.'*" Theories for composite wear have also been presented as 2 main clinicai components: occ lu sal-contact wear and contact-free wear. Occ I usa I-contact wear is a localized process that has been primarily based on theories of microfracture and degradation of the silane coupling agent by hydrolysis and chemical absorption.'"

Contact-free wear (abrasive wear) is a generalized process that has been based primarily on the "protection theory" proposed by )orgensen et al.'^ Fatigue is generally associated with occiusal contact wear while abrasion appears to be the primary mechanism of wear in contact-free areas.

Because of the complex nature of the wear process no in vitro testing device has been capable of simulating ail aspects of ciinicai wear. This is because in vitro testing targets only one mechanism while clinical wear is a mixture of different mechanisms. In addition, some studies found that no significant correlation^"-^' could be made between in vivo and in vitro wear while others found a strong correlation.'^-^^ This study used a 2-body wear device that would primarily measure only 2-body abrasive wear. Tranter et a l " indicated that the 2-body device used in this investigation has the abiiity to rank materials with a 3-body wear device (r = 0.94) and pooied clinical data with a high degree of correiation (r= 1.0).^^ This work suggests that the simple 2-bQdy wear device

The International lournal o( Prosthodontii

used in this study provides a good first approximation of relative contact-free wear rates. FHowever, because the wear mechanisms associated with clinical wear are compiex, in vitro tests may provide a screening mechanism for composite materials.^"'^' Leinfelder et aP* proposed the microfracture mechanism ofwear. The basis ofthis mechanism is that the fiiler particles have a higher modulus than the resin matrix; therefore, they compress during function and produce microfractures. The composite is predisposed to loss of materiai at tbe surface during cyclic loading because the microfractures grow and eventually become connected. Materials with the greatest wear resistance shouid possess a microstructure relatively free of microcracking. Scanning electron microscopy was evaluated for 3 specimens from each group. Figures 2 and 3 are representative SEM views.

Figure 2 shows Herculite, a hybrid composite material in which several microcracks are delected. Figure i shows Concept, a microfilled indirect resin system in which microcracks are not evident. This finding is consistent with the results, in which Concept exhibited 60% less wear ihan Herculite. It has also been suggested that microfine materials such as Concept and Heliomoiar may exhibit minimal wear in shortterm studies but may undergo fatigue-type wear in the iong term because of their lower fracture toughness.^''^^ The wear resistance of composite has been influenced by filler size, filler shape, filler load, and fillermatrix bonding.^'"^'' In general, a significant reduction in the amount of wear is detected by decreasing the size of the fiiler particles.'®-''Other investigations have shown that materials with high volume fractions of inorganic filler exhibit improved mechanical properties.^®--^ Furthermore, chemical treatment of the filler particles to enhance the bond between the filler and resin matrix has been used.^" One study showed a strongcorrelation between si lane-treated fillers and improved wear resistance." In the present study resin systems with high filler volume fractions such as belleClass exhibited significantly less 2-body abrasive wear ihan Artglass and Targis, which have lower filler volume fractions. Concept and Heliomolar exhibited significantly less 2-bDdy abrasive wear than belleGlass; however, these materials are microfills, suggesting that particie size and interparticle spacing may be more critical to a material's resistance to The baseline techniques for degree of conversion used in this investigation followed methods previously employed by Rabek^-* and Rueggeberg eta I.'•' Internal reference peaks and baseiine connections were chosen to minimize interference between absorption peaks. Such interference may result in conversion

436

, Numbers, 7Ö99

2-Body Wear Re^iitance and Conversion of Composites

calculations that may not directly correlate to carbon double bond concentration and infrared carbon double bond absorptionJ33+-'i* The degree of conversion for Heliomoiar found in this study was 48%, which is in agreement with the findings of Ferracane and Condon.-'^ The degree of conversion found for Herculite was lower than that found in a previous investigation.

Heat curing in addition to visibie-light curing has been shown to substantially increase the degree of conversion.^' Highiy polymerized methacryiate materials that are characterized by increased crosslink density tend to exhibit less wearJ' In this study the indirect composite systems with the highest degree of cure aiso tended to show the lowest amount of 2bodyabrasivewear. Concept and belleGiass indirect resin systems are poiymerized under pressure (80 to 85 psi} at an elevated temperature of 120 to 140°C. In addition, belleGlass is cured in a nitrogen atmosphere. Curing under nitrogen with increased atmospheric pressure and temperature shouid increase the degree of conversion through decreasing porosity and increase monomer vaporization in addition to reducing oxygen polymerization inhibition.

when compared to Herculite, a direct microhybrid composite.

4. BelleGlass, a laboratory-processed composite, exhibited significantly less 2-body abrasive wear than Targis and Artglass, 2 of the indirect composites tested.

5. Concept and belleGlass, 2 laboratory-processed composites, exhibited a mean degree of conversion that was significantly higher than any of the other composites tested.

Acknowledgments The¿uihor5acknowledgeWiiliamM. Johnston, PhD, Department oí Restorative Dentistry, Prosthodontics and Endodontics, for expert statistical analysis and lohn C Mitcheli, BS, Senior Electron Micrascopist, Department of Geological Sciences, for technical assistance with the SEM views in the preparation of this manuscript.

This study was supported by The Ohio State University College of Dentistry.

References 1.

1.

Artglass and Targis laboratory-processed composites use novel photo-curing units that combine intense visible light (320 to 500 nm) and heat. To increase the polymerization potential the Artglass pholo-curing unit uses pulsed (20 ms) high-intensity visible light with dark intervals (80 ms), wbich according to the manufacturer allows the already-cured materiai to partially reiax, thus increasing the avaiiabiiity of noncured methacr^'iate groups for additional reaction. In addition to the usual bifunctional dimethacryiates Artgiass contains multifunctional methacrylates with up to 6 reactive groups.^^ Composites processed using the Targis system undergo stages of increasing heat in addition to intense visible light. The relatively high 2-body abrasive wear values of Artglass and Targis demonstrated in tbis study may have been the result of a rapid degradation of iight intensity because of excessive distance between the specimen and iight source during curing. Further study is needed to evaluate this consideration.

3.

4 5.

6.

7

Conclusions 1. Enamel exhibited a mean 2-body abrasive wear rate that was significantiy lower than any of the composites tested.

2. Concept, a laboratory-processed microfill composite, exhibited significantly less 2-body abrasive wear than any of the other composites tested.

3. Heliomolar, a direct microfill composite, exhibited significantly iess 2-body abrasive wear

Volurre 13, Numbers, 1999

resins. I Orai Rehabil 1982;9:493-497.

Caputo AA, Standlee |P. Biomechanics in Ciinicai Dentistry.

Chicago: Quintessence, 1987:107-109.

Ferracane JL. tjsing posterior composites appropriately. | Am DentAssoc1992;123:53-58.

Ferracane JL Correlation behveen hardness and degree of conversion during the setting reaction oí unfilled dental restorative resins. Dent Maler 1935;1:11-14.

8.

Wendt SL )r. The effect of heat used as a secondary cure upon the physical properties of ihree composite resins. I. Diametral tensile strenph, compressive strength, and marginal dimensional stahi I itv. Quintessence Int 1937; 18:265-271.

9.

Ruyler IE. Types oí resin-hased inlay materials and their properties. Int DenI | 1992;42:139-144.

10.

McCabeJF, <agi S. Mechanical properties of a composite inlay material following post-curing. Br Dent 1 1991 ;171 .lA^lA^.

11.

EerracaneJL, Mitchem | C Condon |R, Todd R. Wear and marginal breakdown of composites with various degrees of cure. J DentResl997;76:1,508-1,516.

12.

EerracaneJL, Greener EH. Eourier transform infrared analysis of degree otpolymeiization in unfilled resins—Methods comparison.! Dent Res 1984:63:1,093-1,095.

13.

Uibanski J, Czerwinski W, lanicka K, Majewska F, Zowall H. iHandbook oí Analysis of Synthetic Polymers and Plastics.

Chichester, UK: EliisHorwood, 1977:403^13.

14.

Matr VW. Vt'ear in dentistry—Current terminology. J Dent 1992,20:140-144.

15.

Pugh B. Wear. F r i c t i o n and Wear. L o n d o n : N e w n e s Butterworths, 1973:141-172.

CondonJR,Eerracanc|L. Evaluation of composite wear with a new multi-mode oral wear simulator. Dent Mater 1996;! 2:218-226.

16.

437

Christensen CJ. Don't ijndereitimate the Class II resin. ] Am Dent Assoc 1992;12.1:I03-I04.

Reinhardt |W, BoyerDB, Stephens NH. Effects oí secondary cjring on indirect posterior composite resins. Oper Dent 1994; 19: 217-220.

Albers HE. Direct composite restoratives. ADEPT Report 1991 ;2; 53-64.

InoueK, t-layashi I. Residual monomer (bis-CM A) of composite

l u í Prosthodontics

J-Büdy Wear Resistance and Conversion of Corrposiles

17.

18.

19.

20.

21.

5?

23.

24.

25.

26.

27.

28.

Knobloch et al

Soderholm Kl Richards ND. Wear resistance of composites: A solved problemi Gen Dent 1993;46:256-263.

Bayne SC, Tayicr DF, Heymünn HO. Protection hypothesis for composite wear. Dent Mater 1992,8:305-309. lorgensen KD, Horsled P, fanum O, Krogh ), Schulz ). Abrasion of Class! restorative resins. Scand I Dent Res 1979:07:140-145, PcwerîlM, Ryan MD, Hosking D|, Goldberg A|. Comparison of in vitro and in vivo wear of composites. J Dent Res 1983;62: 1,089-1,091.

Lutz F, Phillips RW, Roulell-F, SetccsJC. In vivo and m vitro wear ot polenlial posterior composites. | Dem Res 19B4;63:914-920.

TranierT, Seghi tA, Seghi RR. Rank correlation between (>j-i'ivo and three in-vitro methods of clinical wear evaluation lahstracl 1,502). J DentRes1997;76:201.

Taylor DF, Bayne SC, Leinfelder KF, Davis S, Koch CG. Pooling of long term clinical wear data for posterior composites. Am | Dentl994;7:I67-174.

Leinfelder KF, Wiider AD, Teiseria LC. Wear rates of posterior composite resins. ] Am Dent Assoc 1986;112:829-833.

Van Groen ingen G, ArendsJ. in vivo ahrasion of composites: A quantitative investigation. Quintessence Int 1981:10:1,101-1,107.

Truong VT, Tyas MJ. Prediction oí in v/Vo wear in poslerior composite resins: A fracture mechanics approach. Dent Mater 1988,4:318-327.

Suzuki S, teintelder KF, Kawai K, Tsuchitani V. Effect of particle variation on wear rates of poslerior composites. Am ] Dent 1995;8:173-178.

Brsem M, Finger W, Van Doren VF, Lambrechls P, Vanherle C. Mechanical properties and filler fraction of dental composites.

Dent Mater 1989;5:346-349.

29.

30.

31.

32.

33.

34.

35.

36.

37.

39.

Germaine HS, Swartz ML, Phillips RW, Moore BK, Roberts TA, Properlie; of mictofliled composite resins as influenced by filler content. J Denl Res 1985;64:155-160.

Vanherle G, Smith DC. Posterior Composite Resin Dental Restorative Materials. Utrecht, The Netherlands: Peter Szulc, 1985:143-147, Condon )R, FerracaneJL. In vitro wear of composite with varied cure, filler level, and filler [reatmenr ) Dent Res 1997;76: 1,045-1,411. lorgensen KD. Occlusai abrasion of a composite resin wilh ultra-fine filler—An initial study. Quintessence int 1978;6:73-78.

RabeklF. Experimental Metbods in Polymer Cbemistry, Physical Principles andApplit:ations,ed 4. New York: lohn Wiley, 1980:80, Rueggeberg FA, Hashmger DT, Fairhjrst CW. Calibration of FTIR conversion analysis of contemporary dental resin composites. Dent Mater 1990;6:241-2 49.

Vosbida K, Greener EH. Effects of two amine reducing agents on the degree of conversion and physical properties of an unfilled light-cured resin. Dent Mater 1993;9:246-2S1.

FeiracanelL, Condon ]R, Post-cure heat treatments for composites: Properties and fractograpby. Dent Mater 1992;8:29(K295, Dionysopoulos P, Watts DC. Dynamic mecbanrcal propeitiesof an inlay composite. J Dent 1989;! 7:140-144.

Leinfelder KF. New developments in resm restorative systems.

I Am Denl Assoc 1997;128:S73-581.

PhotoelastJc stress analysis of load transfer to implants and natural teeth comparing rigid and semirigid contiectors.

A photoelaslic model of a human ieft mandibie edentulous to tiie first premolar was tabricated using two screw-type implants in the positions ot the first and second molars. The "natural" premoiar abutment was prepared using a standard metai-ceramic shouider-beveled tooth preparation. Three types of connection were used: non connection with only proximal contact, rigid solder joint, and nonrigid attachment connection. Both impiants or oniy the distal one were used in different combinations. Simuiated verticai masticatory torces were applied. The least stress was transterred between connected impiants and teeth with the nonngid connector. The jse of ngid connection in the single-i m pi ant situation caused oniy slightiy higher stresses in the supporting structure than the nonrigid connector. The rigid connector demonstrated more widespread stress transfer in the two-implant case, it was concluded that the stresses observed showed adequate distribution tor both the ngid and the nonngid connection.

Nishimura RD, Ochiai KT, Capulo AA, Jeong Ciii. JPrasi/ieIOenM999;8t.698-703 References: 16.

Reprints: Dr Angelo A. Caputo, University of California at Los Angeles SchDol of Dentisir/, Los Angeles, California 90095—SP

Tlie International loumal of Prosthodontics

438

VoiiJrrel2,Number 5,1999

The Effects of Tooth Preparation on Pressure Measured in the Pulp Chamber: A Laboratory Study

Christopher D. / . Evans, BDSc, MDSc' Peter R. Wilson, MDS, FDSRCSEd, MS, DRDRCSEd, PhD''

Purpose: The purpose of this study was to determine pressure changes in the pulp space during tooth preparation with either diamond or tungsten carbide burs in a high-speed dental handpiece in the lahoratory. Materials and Methods: Twenty premolar teeth were collected and randomly assigned to two groups: group 1 received preparation with diamond burs and group 2 with tungsten carbide burs. The teeth were mounted on a pressure transducer and the pulp chambers were filled with saline. A 0.1-mm thickness of tooth tissue was removed from the proximal surface of each tooth, alternating dry and wet cutting, untii the pulp chamber was exposed. Pressure and temperature changes were recorded during tooth preparation. Results: At 0 to 1 mm of remaining dentin depth dry cutting with diamond and tungsten carbide burs generated a mean positive puipai pressure of 12 kPa and 6 kPa, respectively. Wet cutting under the same conditions produced 0.6 kPa and 0.15 kPa, respectively. The difference between wet and dry cutting was highly significant (P < 0.001 ). Diamond burs produced significantly higher pressure increases than carbide burs at all levels for both wet and dry techniques IP < 0.05). When cutting farther than 2 mm from the pulp, tooth preparation created a mean 0.09-kPa pressure increase, which was not influenced by either coolant use or bur type. The temperature change was minimal during wet cutting and only minor temperature increases were recorded during dry cutting. Conclusion: From this laboratory study it is concluded that significant pressure changes occur in the pulp chamber during tooth preparation ot" extracted teeth when the remaining dentin thickness is less than 2 mm.

Int J Frosthodont 1999:12:439-443.

D

entin is a porous, mineralized tissue that is filled with fluid. When the enamel seal is lost millions of fiuid-filled tubules are exposed to the oral

'Private Practice in Frostbodontics. Meibourne. Austraiia. 'â&#x20AC;˘Senior Lecturer, Restorative Dentistry. Tbe University of Meibourne; and Private Practice in Prosthodontics, Melbourne.

Australia.

environment. As the thickness of remaining dentin decreases the tubules increase in both si;ie and number.' If the exposed dentin surface is stimulated fluid can move in either direction along the lubules-^ Preparation of teeth to receive complete-coverage restorations exposes large numbers of dentinal tubules and pulpal necrosis can occur after vital teeth are restored with artificial crowns.^

The purpose of this investigation was to demonstrate whether pulpal pressure changes occur during tooth preparation, to quantify these pressure changes, to investigate pressure changes during both wet and dry cutting, and to examine the differences in pulpal Tbis paper is based on tbe tbesis ofC. D. I. Evans, submitted to thepressure changes with diamond versus tungsten carUniversity of Melbourne in partial fulfillment of tbe requirements bide burs. for the degree of Master of Dental Science.

Reprint requests: Or Peter Wilson. 711 Elizabeth Street.

Meibourne, VIC 3000, Austraiia. Fas: + 613-9341-0437, e-maii: p.wilsoni^dent.unimetb.edu.au

Volume 13. Njmber 5, 1999

439

l cf Prasthodontics

Effects oí Tooth Prepar^ition on Pulp Chamber Piessure

Pressure fransdijcer

adbesive and catalyst (M Bond 200 Adhesive, Henkel 700) reinforced with acrylic resin (GC Pattern Resin, GC) bonded tbe tooth to the transducer tubing.

Thermocouple wire (Type J, Data Instruments) was calibrated and passed through the 1-mm proximal hole. Acrylic resin luted the thermocouple wire to the tooth and provided a watertight seal. Tbe pressure transducer and tooth were flushed witb saline until no bubbles appeared and the valve was then closed.

MacLab (Apple MacLab/4 Analog Digital Instruments, Apple) recorded experimental data.

An 8-mm-long, 1.2-mm-wide cylindric diamond bur (Komet 837KR 012 FG) and a 6-mm-long, 1.2mm-wide cylindric crosscut tungsten carbide bur (Komef H31 L 012 FG) were used. A plastic bag containing a 0.17-N weight of lead shot was connected to the bandpiece platform with twine, passing over the plastic wheel. The tooth and the bur were randomly selected for investigation. A tooth was cut by the same bur, alternating wet with dry cutting, with 6 mm of bur contacting tbe tooth during preparation.

Ten teeth were cut with diamond burs and ten with carbide burs. The Chart 3 software program (AD Instruments) was started to record the pressure change, temperature change, and bandpiece position during preparation.

The handpiece was positioned at the minimum travel position and the table moved so that the tooth was located in ihe bur's path of travel. Tbe bur was run atmaximumspeedforeach cut. After the first pass was made the handpiece was stopped. The vertical handpiece platform was returned to the minimum position on the linear bearing and the tooth table was advanced 0,1 mm into tbe path of the bur- Tooth preparation continued until pulp exposure was detected. Data were transferred from Chart 3 to Microsoft Excel, version 5.0 for statistical analysis-

Handpiece and bur Tcotfi Low-triction rolling slide

Fig 1

Schematic representation of expenmental apparatus.

Materials and Methods A specially constructed apparatus was used to prepare the proximal surface of extracted premolar teeth (Fig ]). An ultrahigh-speed dental handpiece (Pana-Air M3866) was attached to an adjustable vertical aluminum platform mounted on a rail-and-slide assembly (NSK LS15AÍ- Higb-Capacity Linear Bearing, Nippon Seiko) that provided sideways bandpiece movement. Plastic wheels were located at each end of the linear bearing track to allow a hanging weight to pullthehandpieceandbur into and through tbe tooth.

A pressure transducer (MA 01720 Mediamate, Data Instruments) with a mounted tooth (as in Wong and Wilson'') and coolant-collection device was fixed to a table that aiiowed incremental horizontal movement at rigbt angles to tbe bandpiece- Attached to the pressure transducer was an outlet and input 3-way valve. Sterile saline (NaCI 0.9%, Delta West) was used to calibrate the transducer. Premoiars extracted for orthodontic purposes were collected and stored in sodium azide 0.05% solution below 4°C for no more than 6 months.

The roots were sectioned 7 mm from the cementoenamel junction using the high-speed dental handpiece, and a cylindric diamond bur (Komet 837KR 012 FG, Brasseler) was used to achieve a flat surface.

The pulpal tissue was removed from the puip chamber and root canal using a barbed broach (#15, Kerr), witb care being taken not to toucb the internal surfaces of the chamber. The root canal was widened witb acylindricdiamond bur (Komet H31L 012 FG, Brasseler) to approximately 3 mm in width and 5 mm in length without entering the coronal pulp chamber.

This allowed a tooth to fit passively over the stainless steel tubing protruding from the pressure transducer.

A 1-mm-wide hole was carefully drilled through the proximal tooth surface into the pulp chamber opposite the work side, A thin layer of cyanoacrylate

The Infernatlonaf Journal of Prosthodontic

Results

Most teeth received between 20 and 30 cuts, with a maximum of 32 and a minimum of 9- A total of 501 observations was recorded. Large differences between the pressure readings for wet and dry cutting were evident, with the dry being an order of magnitude larger over the entire depth range. This was most obvious when the depth of remaining dentin was small. The pressure ranges for wet cutting were-1.45 to2.50kPa and -0.45 to 34-15 kPa for dry cutting (Fig 2). There was greater variability for dry-cutting data, which increased as the depth of remaining dentin approached 0. A linear model was used for analyzing the wet data. The dry data were divided into 3 groups since there was evidence of clear groupings within which the variance was relatively bomogenous.

440

Volümel2,r^ijmberS,1999

Eíletts of Tooth Preparation on Pulp Chamber Pressure

With wet cutting there was iittie interaction of random sampling effects for drill type or coolant.

The tungsten carbide bur yieided less pressure than the diamond bur (P < 0.05). The use of a watercooled diamond added 0.45 kPa pressure at depths close to the pulp and less than 0.2 kPa with a 3-mm depth of remaining dentin.

The pressure values tor dry cutting were divided into 3 levels based on the depth of remaining dentin: •

Level 1: 0 to 1 mm depth of remaining dentin.

Diamond burs produced significantly more pressure than the tungsten carbide burs at this ievel (P < 0.0005) and considerable variability was noted.

• Level 2: 1 to 2 mm depth of remaining dentin.

Variabiiity was less than at level 1 and there was a significant difference in the trendlines for the tungsten carbide and diamond burs (P< 0.0014), with tungsten carbide burs again yielding less pressure.

• Level 3: > 2 mm depth of remaining dentin. There was no difference in bur type at distances > 2 mm from the pulp. One outlying value was omitted.

The same depth groupings were used to compare wet and dry cutting pressures:

Peak pressure (kPa)

• T = dry tungsten WT = wet tungsten DD = dry diamond WD = wet diamond

n

nn

DT WT OD WO 0-1

n

DT WT DD WD

m DT WT DD WD

t-2

2+

-2Depth of remaining üentin (mm)

Fig 2 Plot of experimental condition and pressure measured in the puip chamber.

•

Level 1 : Diamond burs produced a mean positive pressure increase of 11.64 kPa ISD 7.85) and tungsten carbide burs produced 6.06 kPa (SD 4.40) under dry cutting. Wet cutting produced 0.58 kPa ISD 0.381 and 0.15 kPa (SD 0.481 for diamond and carbide burs, respectively. The difference between wet and dry cutting was highly significant (P < 0.0011 at a 0- to 1 -mm depth of remaining dentin.

• Level 2: The mean pressure increase for wet and dry cutting with diamond burs was 0.41 kPa (SD 0.26) and 3.41 kPa (SD 2.491, respectively, and 0.12 kPa (SD 0.16) and 1.27 kPa |SD 1.37), respectively, for tungsten carbide burs. There was a highly significant {P < 0.001) difference between wet and dry cutting for both tungsten and diamond burs when tfiere was 1 to 2 mm of remaining dentin.

• Level3: When the depth of remaining dentin was greater than 2 mm the pressure difference for wet and dry cutting was significantiy different for tungsten carbide burs but not for diamond burs (P< 0.05).

Dry cutting produced a temperature increase as the depth of remaining dentin increased. A2°C increase occurred with dry cutting at 0.2 to 0.4 mm of remaining dentin with diamond burs. The temperature

Volume 12, Numbers, 1999

441

did nol change for wet cutting with diamond burs. For tungsten carbide burs the temperature was relatively constant for both wet and dry cutting.

Discussion Tooth Preparation Technique The specially constructed tooth preparation device served to control some of the variables associated with tooth tissue removai, thus standardizing each preparation slice, it enabled unidirectional cutting at a fixed angle of approach (90 degrees) under constant ioad. Previous investigators have used similar tooth preparation devices to study tooth cutting interactions and to test bur efficiency.^ Under freehand cutting conditions the load applied to the workpiece varies considerably.''A small load was applied to the handpiece during cutting to reduce the chance of stalling the bur during the preparation slice. This load was comparable to that used in previous investigations.'

The depth of cut in the current experiment was carefuliy controlled so that each pass removed 0.1 mm of tooth tissue incrementaily until pulp exposure occurred. The number of cuts each tooth received varied with the tooth size. Most teeth required between 20 and 30 cuts before the pulp was exposed, indicating a total

The International Journal of Prosthodonlii

Effects of Tooth Preparation on Pulp Chamber Pressure

Evans/Wilson

proximal wall thickness of 2 to 3 mm. The bur rotated in the opposite direction to the handpiece travel to prevent the handpiece from being "pulled" into the workpiece. It was clear, especiaily from the dry-cutting experiments, that proximity to the pulp space allowed more pressure transmission to the pulpal space. It has been shown that fiuid movement across dentin is significantly affected by the tubule radius when surface area increases and/or dentin thickness decreases."

expressed in terms of cellular infiitration and displacement. They found that whiie coolants were adequate to prevent burn lesions they did not prevent inflammatory responses when the cutting technique required force application of greater than 8 ounces (2.5 N).

Beveridge and Brown'^ demonstrated in vivo that grinding and drilling procedures produce increases in intrapulpal pressure. They found intrapulpal pressure changes to be variable during superficial enamel removal, but during deeper dentin removal marked pressure increases were observed. They also noted that pulp exposure did not result in a marked pulpal pressure decrease as occurred in the present study.This can probably be explained by the gelatinous nature ofthe tubuiar fluid that is seen in vivo,^''compared with the saiine used in our laboratory study.

BrännstrÜm et al'^ suggested that the movement of fluid from the pulp toward the tooth apex during cutting results from the frictionai heat of cutting causing fluid expansion. Histoiogic studies on dry cutting have also shown that odontoblasts are displaced into the dentinal tubules opposite the surface being cut, presumably as a resuit of intrapulpal pressure increases.'^ In addition to these effects cutting dentin shatters the mineral matrix, producing substantial quantities of debris that become packed into the dentinal tubules. It is accepted that cutting without water spray generates a thicker smear layer, as does cutting with diamonds compared with carbide burs." Thus, it is possibie that the observed significant pressure differences between wet and dry cutting are the result of tbe dentinal tubules being packed with debris to form a deeper smear layer after each dry cut. This may explain the pressure increase for dry cutting in the presence of small temperature increases, since coolant would aid in clearing cutting debris, thus reducing this packing effect.

The use of diamond burs produced significantly greater pressure changes compared with tungsten carbidebursforbotb wet and dry cutting techniques, as there was more impaction into the tubules.

Pressure atrophy can result from continuous or prolonged pressure on a group of cells. The buiidup of pressure in the dental pulp as a result of operative procedures may induce cell necrosis,^^ In the present study the pulpal pressure increased quickly over the short cutting time (approximately 5 to 10 s), but often required several minutes to return to normal after cutting ceased.

The possibility of these pressure increases being cumulative, while not investigated, cannot be discounted.

Bur Type

The 2 bur types selected for investigation in thisstudy are representative of the burs typicaily available for tooth tissue removal. Diamond burs differ in their cutting action from carbide burs. Diamond burs grind tooth structure, whiie carbide burs cleave tissue from the substrate.^ While the diamond bur used in this study was 2 mm ionger than the carbide bur, simiiar bur lengths were involved in tooth tissue removal.

Lower pressures from the use of carbide burs suggest that the impaction of a srnear layer into tubules may be a factor in the increased pressure from the use of diamond burs.

Thermocouple Position In this study the thermocoupie was bathed in saline and its tip contacted the dentin wali. This reduced the chance of damage to the thermocouple during the cutting procedures and recorded the temperature ofthe pulpal saline. This is simiiar to the technique of Zach and Cohen,^^ but their thermocoupie was batbed in pulpal tiuid. Henschel"* has suggested that since dentin and enamel are good thermal insulators most of the frictionai energy that results at the dentin-bur contact is lost to the environment. This is believed to be the reason the temperature changes recorded by thermocouples situated in the pulp are minimal. In spite of this our intention was to ensure that the pressure increases observed were not related to mass thermal expansion.

Pressure Effects

The present laboratory study found that the removal of superficial tooth structure produced minimal pressure variability, while deeper preparation produced pulpal-space pressure increases.

Physical damage to the pulp during tooth tissue removal may greatly reduce its reparative capacity^' If fluid is forced pulpward during tooth preparation an increase in intrapulpal pressure should be seen.

Stanley and Swerdlow^^ suggest that pressure alone plays a significant role in contributing io the incidence and intensity of the inflammatory response as

The internationiii lojmai of Pro sth odor tics

Temperature Effects Minimai temperature changes were recorded for wet cutting, wbich is consistent with previous studies.'^'^"

442

Voljme 12, Number 5,1999

Effects of Tooth Preparation on Pulp Chamher Pressure

Evans/Wilson

However, our results show that dry cutting produced a maximal temperature increase in the pulp of only 2°C. There is little published literature on the temperature effects of cutting when the depth of the cut and the handpiece load are precisely control led. It has been reported that prolonged dry preparation increases pulp-chamber temperature.''^•-'•-' In contrast, temperature decreases have also been demonstrated during dry cutting.-^ However, the depth of remaining dentin has not been reported, which may explain these observed differences.

The low temperature increase seen in our study for dry cutting could be related to the very thin section of dentin (0.1 mm) removed during each slice or to the thermal insulating effects of dentin.'^"' In addition, the rotation of the dental buratultrahigh speeds produces an air "whirl" or "turbulence."-''-'' As a result the rotating bur moves quantities of air in its immediate area, possibly dissipating heat. In addition, the coolant is probably acting on the entire tooth surface compared with the small contact area of the bur and tooth.-"* The data presented from the current investigation show that intrapulpal pressure changes do occur and can change the pressure significantly during tooth tissue removal. The traditional concept of pulpal damage resulting from frictional heat generation during dry cutting must be questioned. This laboratory study demonstrated that dry cutting generated significantly greater intrapulpal pressures than wet cutting, while generating only small temperature changes. It appears that tungsten carbide burs generate less heat and pressure than diamond burs and this may be the result of different cutting mechanisms.

Wong RH, Wilson PR The effect of seating (orce and diespacing on pulpward cementation pressure transmission, s laboratory study. lntDent|1997,-47;45-52.

Watson T, Cook R. The influence of bur blade concentricity on high-speed tooth-cutting interactions: A video-rate confocal microscopic study. | Denl Res 1995 ;74:1,749-1,755.

Liao W, Taira M, Ohmoto K, Shintani H, Vamaki M. Studies on dental high-speed cutting. ] Orai Rehabil 1995;22:67-72.

Siegel S, Von Fraunhoffer |. Assessing tlie cutting efiiciency of denial diamond burs. I Am Dent Assoc 1996;] 27:763-772.

Reeder O, Walton R, Livingston M, Pashiey D. Dentin permeability: Determinants ot hydraulic conductance. | Dent Res 1978; 57:187-193.

Morrison A, Grinnell H. The theoretical and functional evaluation of higher speed rotary inslrumentation. | Prosthet Dent 1958;8:297-314.

Henschel C. Heat impact of revolving instruments on vital dentin tubules. 1 Dent Res l943;22:323-333.

Bergenholtz C. latrogenic injury to the p j l p in dental procedures: Aspects of pathogènes i 5, management and preventive measures.

I n t D e n t I 1991 ;41:99-110 Staniey H, Swerdiow H. Biologic efiects oí various cutting methods in cavity preparation: The part pressure plays in pulpal response. J Am Dent Assoc 1960;61:45CM56.

Beverid^e E, Brown A. The measurement of human dental in13. B trapulpal pressure and its response to clinical variables. Oral Surg Oral Med Oral Pathoi l965;19:6S5-6&3.

Liridén L, Kallskog Ö, Woigast M. Human deniine as a hydrogel. Arch Oral Biol 199S;40:991-1,004.

Brännström M, Linden L, Johnson G. Movement of dentinai and 15. B puipal fluid caused by clinicai procedures.] Dent Res 1963;47: 679-632.

Swerdiow l-l,SlanleyH. Reaction of the human dentai puip to cavity preparation. I. Efiect of water spray at 20,000 rpm. ] Am Dent Assoc ]958;56:3]7-329.

Pashiey DH. Smear layer: Physiologic considerations. Oper Dent 19fl4;suppl 3 1 3 - 2 9 .

Setaer S, Bender 1. Early human p j l p reactions to fuil crown preparation. I Am Dent Assoc I959;59:915-923.

Zach L, Gohen G. Thermogenesis m operative techniques: Comparison of four methods. | Prosthet Dent 1962;12:977-984.

Langeiand K, Langeiand L. Gutting procedures with minimized trauma. I Am Dent Assoc I963;76:991-l,005.

Laforgia P, Milano V, Morea C, Desiate A. Temperature change in the p j l p chamber during complete crown preparation. ] Prosthet Dent199];6S:56-6l.

Goodis H, 5cheiii B, Stauffer P. Temperature gradients at two locations within the toolh during cavity preparation in yitro. 1 Prosthet Dent 198e;60:6ö4-68e.

Bhaskar5, Lilly G. Intrapulpal temperature during cavity preparation. I Dent Res 1965;44:Ë44-647.

Schuchard A, Watkins C. Thermal and histological response to high.speed and ultra high-speed cutting in tooth structure. I Am DentAssocl965;7I:l,4SI-t,453 Langeland K. Prevention of puipal damage. Dent Clin North Am 1972;16:709-732.

Acknowledgments This Study was s u p p o r t e d by grants t r o m the A u s t r a l i a n Prostbodontic Society and tbe university ot Melbourne. The authors wish to acknowledge Mr P. Barnes for his technical assistance and Mr M. Phillips, Statistical Centre, University of Melbourne, tor his statistical assistance.

References 1.

Gaberoglio R. Brannstrom M. Scanning electron microscopic investigation of human dentinai tubules. Arch Oral Biol 1976;

2.

3.

21:355-362.

Pashley D. Clinical correlations of deniine structure and function. I Prosthet Dent 1991 ;66:777-73].

Bergenholfz C, Nyman S. Endodontic complication following periodontal and prosthetic treatment of patients with advanced periodontal disease. 1 Periodontoi 19S4;55:63-6a.

V o | j m e l 2 , Numbers, 1991

443

Tlie InterraiionsI ¡ojmal of Prostliodnntii

Bo Bergman, LDS, Odont Dr^ Susanna Marklund, LDS'' Hans Nilson, LDS" Sven-Olof Hedlund, LDS''

An Intraindividual Clinical Comparison of 2 MetalCeramic Systems

Purpose: It has been questioned whether the surface and color of the ceramic and the metal-ceramic bond strength of a titanium-ceramic system are comparable to ihose of a conventional noble alloy-ceramic system. It was therefore the aim of this study to carry out an intraindividual clinical comparison between crowns fahricated according to the Procera system (titanium copings veneered with a low-fusing ceramic} and nobie-alloy copings veneered with a medium-fusing ceramic. Materials and Methods: Twenly-one crown pairs were fabricated for eighteen patients; three of the patients were each provided witii two crown pairs. After 2 years nineteen crown pairs in sixteen patients could he compared.

Clinical examinations were performed by two calibrated dentists who are long experienced in prosthetic dentistry. The crowns were rated according to the Califomia Dental Association system. In addition, Bieeding Index and Margin Index were evaluated. Results: After 2 years the quality of surface and color ofthe ceramic material seemed to have deteriorated more in titanium-ceramic crowns than in conventional metal-ceramic crowns, aithough the difference was not statistically significant. Regarding anatomic form, margin integrity, Bleeding Index, and Margin Index the differences between the two crown systems were small. Conclusion: The low-fusing ceramics have been subject to improvements during the last few years. Their bond strength to titanium seems to be comparable to that of conventional metal-ceramic systems. However, in the long run one problem may be the surface and color stability of low-fusing ceramics. To make extended long-term comparisons between the two metal-ceramic systems possible the present patient material will be followed fora longer period than the current 2 years. Int J Prosthodont 1999;! 2:444-^47.

C

ommercially pure (CP) titanium has been used for 10 to 15 years in fixed prosthodontics. A number of studies has evaluated the clinical performance of titanium copings veneered with composites or low-

fusing ceramics. Composites have shown some obvious long-term shortcomings as veneering material' andthereforethetendencytoday is for low-fusing ceramics to predominate. During the last few years some studies have been presented on Procera-fabricated titanium-ceramic crowns (Nobel Biocare).

•'Professor Emeritus and Former Chairman, Department of Generally the short-term clinical results with lowProstbetic Dentistry, Faculty of Odontology, Umeá University, fusing ceramic-veneered Procera titanium copings Sweden. have been satisfactory.^"^' In a long-term study, however, oneof the California Dental Association (CDA) factors, surface and color, showed obvious changes p in the low-fusing ceramic used for veneering during Odontoiogy. Umea University. Sweden. ''Assistant Professor, Department of Dentai Materiais Science. a follow-up period of 5 to 6.5 years.'' It should be Facuity of Odontology. UmeS University, Sweden. noted that the Procera ceramic used in these earlier Reprint requests: Prof Bo Bergman. Department of Prostbetic studies represented first-generation low-fusing ceDentistry, Faculty of Odontology. Umeá University. Si-90187 ramics, and furthermore that no controls with other Umeê, Sweden. Fax: + 4690-774460. metal-ceramic systems were included.

The Intern a liona i Journai ol Proslliodontics

444

Volume 12, Njmber S, 1999

Intraindividual Comparison of 2 Metal-Ceräinic Systems

Bergman etal

In tbe present clinical study intraindividual comparisons were made between titanium copings veneered with a low-fusing ceramic and noble-alloy copings veneered with a medium-fusing ceramic.

used: P< 0,0 i significant; 0,01 < P< 0,05 almost significant; and 0,05 < P not significant.

Materials and Methods

All 18 patients could be followed during the 2-year period. However, there were some complications witb 4 crowns:

Results

Between 1994 and 1996, 42 crowns were fabricated for 18 patients by 5 clinicians, 28 crowns in the Public Dental Health Service and 14 in private practices in the county of Västerbotten, Sweden, Of the patients 12 were women and 6 were men with a mean age of 51 years and a range between 33 and 69 years. Of the teeth crowned tbere were 16 in tbe maxilla and 26 in the mandible; 2 were canines, 16 were premoiars, and 24 were molars. Half of the crowns were fabricated with a coping in a noble alloy (MK-100 gold alloy, )S Sjodings) veneered with a medium-fusing ceramic (Ivoclar Classic, Ivoclar), hereafter referred to as MKIvo, and the other half were fabricated with a coping in CP titanium veneered witb a low-fusing ceramic (Procera ceramic, Ducera), hereafter referred to as TiPro, The titanium copings were fabricated using a combined method ofcopy milling and spark erosion,^ Each of 15 ofthe patients was provided with one crown pair consisting of one MK-[vo and one Ti-Pro crown, which were placed on tbe same category of tooth, ie, canine/canine, premolar/premolar, or molar/molar.

Each of the 3 remaining patients was provided with 2 crown pairs. In tbis way intraindividual comparisons between the 2 types of metal-ceramic crowns couid be made. Whenever possible contralateral teeth were used for the crowning- Whicb teeth in a pair would be provided with the Ti-Pro crown and the MK-lvo crown was determined by lot after preparation and impression taking- The Study design was approved by tbe Human Research Ethics Committee at Umea University.

•

•

•

•

The crowns were examined shortly after cementation (baseline) and after 1 (Re-ex 1) and 2 years (Re-ex III, The clinical examinations were performed by licensed specialists in prosthetic dentistry. The crowns were rated according to the CDA system,'' Bleeding Index^^ and Margin Index^ ' were also evaluated- Details of the examination methods were presented in an earlier report.

Statistical Methods The Chi-squared test was applied to test whether differences regarding the CDA factors within and between the 2 groupsofcrownscould be explained by mere chance or represented real differences.

Differences within each group of crowns between baseline and Re-ex II were tested, as well as differences between tbe 2 groups of crowns at baseline and Re-ex II. Tbe following levels of significance were

Voljme12, Niimber5,1999

445

One Ti-Pro crown loosened after the first month and was recemented. After another 2 months the tooth exhibited a pulpitis- The crown was removed, thetootb was endodontically treated, and the original crown was recemented. This crown is still included in the study, One tooth provided with a Ti-Pro crown was endodontically treated during the first 12 months.

The original crown couid then be used. This crown is still included in the study, One tooth provided with an MK-[vo crown had to be treated endodontically after 8 months and was then provided with a cast post and core and a new crown. This crown was exciuded from the study, One Ti-Pro crown became ioose after 18 months.

Because of a 2-month hospitai stay the patient could not go to the dentist for examination and relevant treatment. During the hospitai stay caries had probably arisen and the situation necessitated the fabrication of a new crown. This crown was excluded from the study.

Thus, 2 crowns and their corresponding paired crowns were excluded from the study and the comparisons were limited to the remaining 19 crown pairs in 16 patients. The latter figure is a resuit of the fact that tbe 2 excluded crowns bad been piaced in 2 patients with one crown pair each- The crowns that were exciuded were removed from the study for reasons that had no connection with the factors studied and do not therefore compromise the results, CDA Ratings The initiai evaluation of tbe factor surface and coior at baseline was very simiiar for the 2 groups of crowns (Tabie 1 ), Dfjring the foiiow-up period some changes from excel ient to acceptabie were noted for the Ti-Pro crowns. The changes were seen as slightiy rough or pitted but sti 11 polishable surfaces. The difference between baseline and Re-ex II, however, was not statisticaiiy significant. For the MK-lvo crowns the evaluations were very simiiar on ail 3 occasions. The difference between the 2 groups at Re-ex ii was not statistically significant.

Regarding anatomic form the initial evaiuations were simiiarfor the 2 groups of crowns (Tabie 2), The

The [nternafional lournal of Prosthodontic

Intraindividual Comparison of 2 Metiil-Ceramic Systems

Table 1 Comparison of Ti-Pro Crowns (n = 19) and MK-lvo Crowns (n Regarding Surface and Color Ti-Pro crowns

MK-luo crowns

Baseline

Re-ex 1

Re-ex II

Baseline

Re-ex 1

Re-ex il

16 3

14 5

12 6 1'

16 2

18

17 1

Satisfactory Excelient Acceptable Not acceptable

It

It

1t

'Gross porosilies in the ceramic.

Table 2 Comparison ot Ti-Pro Crowns (n = 19) and MK-lvo Crowns (n = 19) Regarding Anatomic Form Ti-Pro crowns

MK-lvo crowns

Baseiine

Re-ex 1

Re-ex II

Baseline

Re-ex 1

Re-ex II

17 2

15 3 1*

14

15 3 1t

15 3

17 1 It

Satislactory Exceilent Acceptable Not acceptabie

4

r

It

"Faulty conlact. jied

Table 3 Comparison of Ti-Pro Crowns (n= 19) and MK-lvo Crowns (n = 19) Regarding Margin Integrity Ti-Pro crowns

MK-lvo crowns

Baseline

Re-ex 1

Re-ex II

Baseline

Re-ex 1

Re-ex II

18 1

18 1

IB 1

17 2

19 â&#x20AC;&#x201D;

19 â&#x20AC;&#x201D;

Excellent Acceptable

Table 4 Comparison ol Ti-Pro Crowns {n = 19) and MK-lvo Crowns (n = 19) Regarding Number of Bieeding Gingival Surlaces Mesia

Baseiine Re-ex il

Buccal

Distii\

Lingual

Ti-Pro

MK-ivo

Ti-Pro

MK-lvo

Ti-Pro

MK-luo

Ti-Pro

MK-lvo

7 12

11 9

7 5

9 6

1Q 9

8 10

B 5

7 7

small changes within each group up to Re-ex II were not statislically significant, nor was the difference between the groups at Re-ex II. The margin integrity was evaluated as satisfactory in both crown groups throughout the 2-year period.

In fact, almost all crowns showed an excellent marginal fit (Table 3).

(Tabie 4). At this location the MK-ivo crowns showed a higher number of more pronounced bleeding surfaces at baseline compared to Ti-Pro crowns; the reverse was seen at Re-ex il. The differences, however, were comparatively small.

Bleeding Index

There were no systematic differences between the 2 crown groups at baseline or at Re-ex II. The changes thai had occurred during the follow-up period did not show any pronounced shift from one margin level to another, except for lingually among the MK-lvo

Margin Index

The number of gingival surfaces with bleeding did not differ substantially between the 2 crown groups either at baseiine or at Re-ex II, except for the mesial site

Tiie Internationai Journal of Prostliodontics

44g

Volume 12, Numbers. 1999

Intraindividual Comparison of 2 Metal-Ceramic Systems

crowns. At this location Margin Index 3 had increased substantially at Re-ex II. Discussion The number of patients and crown pairs is certainly limited in the present study. However, it is not easy to collect a patient material suitable for a study of the present kind, in which the purpose was to make intraindividuai comparisons between 2 difterent kinds of metal-ceramic systems. This may expiain why such a study does not seem to have been published eariier.

The present study has to be evaluated in light of this.

There is a strong tendency today for artiticial single crowns to be fabricated in ceramic only, without any coping in metal or metal alloy, while a metal-ceramic technique sti!i predominates in fixed partial dentures.

The reason for the use of a metal-ceramic technique for single crowns in the present study was that when the study started in 1994 this method was still widely used tor that kind of restoration. Bearing this in mind and with regard to the factors under study it was estimated that single crowns would be suitable for the intraindividual comparisons to be made. The possibility' of using fixed partial dentures was excluded because our experience led us to conclude that it would have been even more difficult to collect a patient material in which the present study design could be applied.

The differences between the 2 types of crowns were, with one exception, small. Regarding the factor surface and color of the ceramic the outcome seemed to be better for the MK-lvo crowns than the Ti-Pro crowns.

The difference, however, was not statistically significant. In our previous studies'" it was found that no change occurred in Ti-Pro crowns up to 14 to 18 months after baseline. However, after26 to 30 months a marked change was noted; this change was still more pronounced after 60 to 78 months. It would therefore be interesting to try to discover whether a comparison of the 2 types of crowns in the present study will disciose an even greater difference after another 3 years regarding surface and coior of the ceramic materials.

During the follovv-up period one ceramic fracture was noted. It occurred distobuccal of an MK-Ivo crown on a mandibular second molar, where ceramic material loosened from the underlying metal coping. The defect was polishable and caused no functional or esthetic impairment. The present results have shown that the metal-ceramic bond strength between titanium and the low-fusing ceramic used compared well with that ofthe noble alloy and the medium-fused ceramic used.

Persson and Bergman^^ reported in an in vitro study that 2 titanium low-fusing ceramic systems showed even higher shear strength values than a high-gold ceramic system used as a reference. The results from the 2 stud-

VolumeI2 Nurrber S, 1999

447

ies show that low-fusing ceramic-veneered titanium copings compare weil with conventionai metal-ceramic crowns in terms of metal-ceramic bond strength.

The present patient material will be followed for another 2 years. The principal aim will be to try to determine whether the difference between the 2 groups of crowns regarding surface and color of the ceramics will remain or change, but a secondary aim will be to study whether the bond strength is still satisfactory.

During the iast few years the low-fusing ceramics have been subject to improvements. Their bond strength to titanium seems to be comparable to that of conventional metal-ceramic systems. However, one problem in the long run may be the surface and color stability of low-fusing ceramics. To make extended long-term comparisons between the 2 metal-ceramic systems possible the present patient material will be followed for a longer period than the current 2 years.

Acknowledgments This study was supported financially by the Faculty of Odontology, Umeâ tjniversíty and the County Council of Västerbotten, Sweden.

Robert Johansson, BA, the Oncological Centre, Umeâ University, WÜS consulted about the statistical method used

References 1.

2.

3.

4.

5.

6.

Bergman B, Nilsson H, Andersson M. Dentacolor as veneering material for titanium. Swed DentJ 1994;18:25-28.

Reppel P-D, Walter M, Boning <. Metallkeramisther Zahnersatz aus Titan. Dtsch Zahnarztl Z 1992:47:524-526.

Nilsson H, Bergman B, Bessing C, Lundqvist P, Andersson M. Titanium copings veneered with Procera ceramics: A longitudinal study. Int J Prosthodont 1994;7:115-119.

Lovgren R, Andersson B, Bergqvist S, Carlsson CE, Ekström P-F, Ödman P, SundqvistB. Clinical evaluation of ceramic veneerod titanium restorations according to the Proceia technique. Swed DentJ 1997:21:1-10.

Chai J, McGivney CP, Munoz CA, Rubinstein |E. A multicenter longitudinal clinical trial of a new system for restorations. J Prosthet Dent 1997,77:1-11.

Smedbergl-I, EkenbäckJ, LothigÍLsE,Arvidson K.Tivo-yearfo!low-up study of Procera ceramic fixed partial dentures. Int | Prosthodont1998;11:145-149.

7.

Bergman B, Nilson H, Andersson M. A longitudinal clinical study of Procera ceramic-veneered titanium copings. Int | Prosthodcnt 1999:12:135-139.

8.

Andersson M, Bergman B, Bessing C, Ericson G, Lundqvist P, Nilson H. Clinital results with titanium crowns fabricated with machine duplication and spark erosion. Acta Odontol Scand 1989; 47:279-266.

9.

California Dental Association. Quality evaluation for dental care. Guidelines for the assessment oí ciinicai quality and professional performance. Los Angeles: CDA, 1977.

10.

LenOïJA, Kopczyk RA. A clinical system for scoring a patient's oral hygiene performance. | Am Dent Assoc 1973;86:349-852.

1 i.

Silness). Periodontal conditions in patients treated with dental bridges. J Periodontal Res 1970;5:60-68.

12.

Persson M, Bergman M. Metal-ceramic bond strength. Acta Odontol Scand I996;54:l 60-1 65.

The International lournal of Prosthodontii

internalional College of Proslhodontists

The Eighth Meeting of the International College of Prosthodontists Stockholm, Sweden July 7-10, 1999

Program Co-Chairmen: Dr Terry Walton and Professor Brian Monteith Focus Session Topics (Chair) I. Longevity of Prosthodontic Treatment (Terry Walton) II. Prosthodontics Without the Glitz (George Zarb) III. The Posterior Edentulous Mandible (Bernard Smith) Short Paper Session Topics (Chair) Fixed Prosthodontics (Peter |ohnson) Removable Dentures (Rhonda Jacob) Dental Materials (Ken Malament) General Prosthetics (Patrick Lloyd) Meet the Future: Information Technology {Brian Monteith) Occlusion, Oral Physiology, and Temporomandibuiar Disorders (Yasumasa Akagawa) Implants (Douglas Chaytor and Bengt Owall) Maxillofacial Prosthodontics (Bengt Owall)

Abstracts The abstracts for the three Focus Sessions are grouped according to the session in which they were presented. The presentations for the Short Paper Sessions are listed alphabetically by author, grouped by specific session. Because of space limitations. Poster Presentation abstracts will be pubiished in the next issue of the journal (Voiume 12, Number 6, 19991.

Focus Session I T. Atbrektssan. Göteborg. Sweden Longei/ity ol Proslhodomic Treatment— implants Many so-called long-term studies ot oral implants are ot an un acceptably poor quality.

What is termed 5-year success in many sludies represents only 0- to 5-year survival wlien examinad critically. Unaccounted tor patients are not reported and the frequency of recall is not mentioned. Advice On hoiv to adequately present ciinicai data has been published lAlbrektsson and Zarb, 1993; Zarb and Albrektsson, t99B, Albrektsson and Zarb, 199B). The long-term outcome of cylindric, unthreaded titanium irr plants has been poor because of the lacK of steady bone levels dependent either on periimplantitis (rough surfaces) or overload (no threads) (Aibrektsson, t993;Haasetai, 1996). Clinical results of hydroxyapatite-coated implants tiave stiown promising figures for short-term observation

but lamentably poor success rates over 5 years or more lAlbrektsson. 1998). As indicated by Roos et al (t997), positive 5-year data only exist tor Bránemark (Nobel Biocare), Astra (AstraTech), and ITi ¡Straumann) screws.

However, the only paper wilh acceptable 5year figures witti the latter design (Cochran et al, t997) does not contain any bone height measurements. If special emphasis is put on implants placed in bone of poor qualify and quantity, the only positive data {> 90% success) has been pubiished on Bránemark screws by Bahal (t993) and Friberg (t999), with data lacking on other implant systems.

J. Strub, Freiburg, Germany Longevity ol Fixed Partial Dentures The longevity ot dental restorations is an important health concem forthe patient, the ciinician, tbe dental technician, and Ihe various forms of insurance systems Fenv studies document the outcomes of tooth-supported fined prostheses. Creugers et al (1994) aliuded to the difficulty in making comparisons between different studies because no uniform evaluation

The International loumal of Proithodontics

448

standards had been established. They listed several criteria thai should be addressed many meaningful outcome-reporting protocol.

Common criteria tor classifying a tooth-supported fixed prosthesis as successljl include the provision that the prostheses remain in situ and virtually unmodified. There is a lack of consensus as to when adjustment, modification, or repair would representprostheticlailure, butarsmake, even if the abutment teeth remained intact, would certainly render the prosthesis to be classified as having failed Walton (t997) presented a classification system for reporting outcomes of tooth-supported fined prostheses.

In defining the retreatment categories it was considered necessary to distinguish between procedures involved in routine maintenance and those requiring modification, repair, or remake of the prosthesis. This presentation wilt review the information that is currently avaiiabie ir the literature pertaining to longevity of fined partial dentures and will propose criteria enabling a compilation of quantifiable data in future researcli that will reconcile patient, clinician, dental technician, and treatment provider expectations of longevity.

Internalional College of Prosthodontists

R. Jacob, Houston, Texas Denture Longevity: Who Decides?

Compiete denture longevity can be measured in the broadest serse by how long the denture materials remain intact or how long the dantures remain weii adaptea to ihe tissues. As prosthodontists we consider occlusion, retention, and stability. Our patients are more likely to consider comfort and ability to eal. The literature has shown that these 2 considerations are not always compatible when it comes to diagnosing the demise of a given pnjsthesia.

Population statistics ot denture use and longeuity are quite skewed to a select cohort ot subjects: those who seek dentai care. This presentation will discuss cun-ent knowledge as it relates to denture longevity.

N. Creugers, Nijmegen, Tha Netherlands Longevity Studies in Adhesive Prostbodontics Reported service lengths lor certain dental restorations difter substantially. Besides ciinicai parameters différent research methodologies areoonsidersd to be a sigrifoant cause ot ambiguous overall conclusions. In the companson of data from different sources so-called metaanalyses are increasingly used in dental sciences. The application of ttiis type ot research evaluation in medicine has a histofy that goes back to Itie early t930s. Today it has been reoogniiefl as a powerful statistical tool tor inference of treatment results, above subjective review papéis. In this lecture data derived ffom some mefa-analyses will be used for durability assessment of some typical adhesive prcsthodontic reste rations. A meta-analyses-based companson among conventional, implanf-supported, and adhesive Looth replacement wiii be presented, in modem mefa-anaiyses criteria are used for quality assessment ofthe included dinicai studies. The guideiines listed tor this purpose wiii be discussed with respect to their value in evidence-based dentistry. Although ¡t seems ciear that study quaiity is extremely importarlfor the study outcome, ttiere are indicaIcns that on the scale of a meta-analysis fhe quality of individual studies is of iess significant value. A comparison ot 2 recently pubiished meta-ahalyses of fixed partiai denfure survival stows thaf fhe results were quite similar even ttough different sefs of studies were invoived.

AlfriDugh meta-anaiyses are not tiue reproducible "experiments." this anaiogy suggests that they produce consistent results. This controversy will be used to open the discussion about the need fororileria for future research.

J. WoHaardf, Edmonton, Alberta, Canada Quality Management—A Clinical Tool for Globalizing Treatment Outcomes Historically healthcare workers have feiied on regulatory bodies to determine ihe safety of biotechnoiogies for release into ciinicai use.

Typically this was faiiowed by product acceptance based on peer leadership opinion. In this modei there was no requirement for decisions leading fo product acceptance fo be based oh data from randomized oontroiied triats.

Evidence-based medicine (E-BM) and disease man age me nf (DM¡ are strategies thaf have

evotved fo move to a new era of decision making in healthcare. These strategies have arisen from pressuresto provide optimal care overthe lifetime of an individual and to coordinate resource management across a healthcare delivery system. Regulatory bodies wili continue to inliuencethemart(et but their role in product acceptance will presumabiy be reduced. By contrast, E-BM and DM are iikely to iiave a protound effect on the tufure of osseointegrafion bioteciinoiogy. The challenge for the clinician is to have fhe means to participate in an E-BM/DM-driven future. Asan E-Btifl/DM approach to osseointegration evoives the corollary will be tor ciinicians to be abie toevaiuate their own treatment outcome performance againsf the E-BM/DM standard. This perfomiance is also iikeiy to be evaluated against locai, nationai, and international outcomes achieved in a ciinicai setting. As with the estabiishmentof E-BWDM. there needs to be a widely understood means of evaiuating treatment outcomes achieved outside ot a research environment. Ouaiity management is a tool fhaf, when appropriately applied, can provide fhe clinician with means ot participating in afuture where decision making is based on responding fo treatment outcomes that reiate to EBWDtJl. An ÍSO9000 Ouaiity System has been devetoped and implemented for osseointegration. The intent and applicafion of this qualify system wiii be discussed.

Focus Session II p. Garefis. Thessaloniki, Greece Low-Budget Treatment ot Extensive Tooth Wesrana Erosion The evaiuation of an extensive questionnaire reveals thaf there is a prejudice in fhe Greek popuiatioh af iarge againsf removabie parti at dentures, which are considered cumbersome and bulky for the agitated Greek conversation a i sfyie, whiie compiete dentures are regarded as the badge of otd age. The nature of the Greek Heaith Sen/ice means that most patients haue fo pay for their own prosthodontic dentai trcatmenf. Many patients of average income come toa pnvafepracfice demanding impiants and ceramic crowns at a cost that wouid absorb severai months' saiary. Sometimes this arises not so much fromfeeiings of vanity but from the belief fhat paying for fhe best in ferma of materials and technology is a worthwhlie investmenf when dealing with their own heaith. As prosthodontists we need to pause for thought and consider how we can turn our skiii and e>penence tofhe benefit of the majorify. The aim of [his presenlation isfo illustrate some lower-cost altematives wiftv out compromising heaith or function and providing an acccptabie appearance. We also discuss ¡he reactions of patients to these alternatives. We present a case thaf exempiifies many aspects of ftie probiem A 26-year-oid patient presented with extensive erosion ot his maxiilaryteeth caused by the effects of frequent vomiting, vihich had ceased S months previously. The initial treatment planning inciuded endodontic treatment of anterior feeth and rehabiiitation of ali maxillary teeth by fuli-cast veneeredciowns.Thetotaicosf was prohibitive.

Volume 12, Number 5, 1599

449

and as an alternative solution we used a complete overdenture covering all exislingmaniilary teeth. After a years ot acceptable runcticn the patient was able lo afford tiie inifial treatment pian Now, 22 years after the initial therapy the patient, who has annuai checkups, is teeiing comfortable and there are only minor problems caused by the discoloration and v/ear of the acryiic veneers, which wiii be resolved by the repiacement of 6 anterior crowns. We aiso present 2 contrasting cases that enabie comparisons to be made about cost and effectiveness.

J. Hobkirk, London, Unifed Kingdom The Tooth-Supported Overdenture Patterns ot orai disease in the United Kingdom have changed significantiy in recent decades.

LeveisofedentullsmcontinuetofaN, orai health awareness has nsen, management cf the aging partially dentate patient is becoming a signiticant consideration, private funding of treatment is more common, and the pubiic is aware of and increasingty requests techhic^ty complex frealment. This paper will present 2 patients drawn from our pooi of ever 1,000 hypodontia cases, who have for over 20 years since their iatechitdhcod been treated wifh conventicnat overdentures. They represent the dental cripple wifh significant tooth surface loss. Today we wouid often regard impiant freafmonf as fhe ideai for such situations, indeed, tor hypodontia cases most state funding agencies woutd recogni?e an imperative to provide resources for this. For noncongenitat causes the pafient might be strongly recommended to do so, yet is this advice sound? The pafients, both female, tack the majority ot their teeth and demonstrate excessive interocclusal space and coliapsed facial protiies. The problems related to their management wiii be considered and their treatment and its outcomes in terms ot patient satisfaction and orai funclion wiii be described. One patienf, a heaithcafo worker now in middle age, has refused impiant therapy, citing safisfaction with her conventionai overdentures. The other, a somewhat younger executive, now requests the perceived benefits of imptant therapy. The resource impiications and iifestyte impact of fhese 2 treafment modalities will be considered

P. Lloyd, towa City, Iowa In With the New But Not Out With the Ola With the introduction of castabte ceramic restorations, advanced dentin bonding sysfems, and dentai implants to the prosthodonfist's armamentarium many of our iess sophisticafed iow-tech treatments are fatting by the wayside.

Discarding the oid in favor of the new is nof unique fo prosthodontics; it seems to be fhe nomial response when dramatic, miracie-iike developments are introduced. Touted as being more practitioner friendly, more scientificaiiy based, and more long tasting, new innovations offen prematureiy jettison Ihe "oid standard."

Convenfionai prosthodontics. from singiepartiaiveneer restorations to compiete rernovabie dentures, have se n/ed our patients weii for decades and couid. If chamfBoned by those wiw vaiue fhe merits of the time tested, stay in Ihe mainsfream ot treafment options for yeais ahead. To accomplish this, more traditionai prosthodontic

The Intcrnauonai lou al of Prosthodonlics

Infernalional College ot Prosthodontisis

treatments need fo be chronicled wifh detailed reporfings of longifudinal oulcomes so tfiat fhs profession can befter iLdge "wtiaf works and wtiat doesn'f." Ulfimately, ffiose freafments \fiat predicfably and economically serve patienfs best, regardless ot how "old-fasfiioned" fhey are perceived fo Be, could be idanlified and retained as part cf fhe prostfiodonfic opfions lor pafienfs Tfiis presentafion provides a detailed review of a pafient who received prosfhcdcntic care a decade age using a more fiadificnal, Isssfechnology-drivenapproacfi. Pretreatmenf data otfer a clear view of tfie patient's condition and circjmsfances fhal di reefed fhe course ot care. Clfnical infcrmafion ontlie pafienfs status years later reveals fhe degree fo which ihifial decisions were correct An accounfing of services provided during the posftreafment period adds furtfier insighf as ic the relafive appropriateness ot treatment rendered.

P, Owen, tWedunsa, South Africa Prosthodontic Treatment in a Developing Country: Converting "High-Tech" to "Appropriate-Tech" Souffi Atrica is a middle-income developing coLnfry wifh a wide disparify befween liigli- and low-income groups The majority of the popjlaïon relies on public fiealth sector services and remains disadvantaged socioeconomically.

Liberation in 19S4 l:om the oppressive apartheid regime has nol meant immediafe wealth, but seen in the confexf of globalization the Soutfi African economy has fared well. However, reOisfribufion requires growfh and the economy has nof grown af a sufficient rate to enable a tull r^nge of healtfi sen/ices for all The sociopolitical and socioeconomLc disparities of so many years ot oppression fiave resulted in wide gaps in healfh sfafus, with fhe majonty ot tfie population sufteiing from diseases of poverty.

Discriminatory healfh service provision fias meant fhat in fefmsotoral heaIfhcare most people were oftered only extracf ions. Increasing urbanizafion in the last decade or so has also meanf, in marked ccntrasf to developed counfries, increasing rafes ot dental care. All fhis has conspired to create an enormous backlog of dental treatment need, especially tor prostliodarfic rehabilifation. Our challenge lias therefore been to provide sue li freafment in fhe mosf cosfettecfive manner buf wifhouf compromising any proslhodonfic principles. Infhe2dentalschcols in the counfiy dedicafed fo fhe ideals ot fhis type Dl sennce provision sue li f leaf menf iias become commonplace. And the challenge has always been fo convert Ihe "high fech" of lirsf-world prosthodonticsfofhe appropriate technology of an oral healfhcare sysfem based on the philosophy ot fhe primary healfhcare approach. This presenfafion will use, as an example of this approach, fhe principles of the consfruction of acrylic-based removable partial denfures to Shew fhat fhese can and do proi/ide as effective 3 solution 10 prosthodonfic rehabilitation as more compte« alfernatives. Ih addition, similar comparisons will be made befween cosf-effective treatment provision and high-cost alfemafives.

H, Tanaka, E. Mush I m oto, Mo ri oka. Iwate, Japan An Alternative Treatment in a Case with Ad^ancBä Locaiizeä Attrition Evaluation and establishment ot fhe occlusal vertical dimension is particularly important in treafmenf not only of complete denture wearers, but also partially edentulous denfure patients wifh overclosed or collapsed occlusion caused by advanced localized attrition. These sifuations may cause atrophy and paratunction of fhe tempo romand i bular pinfs. The patienf was a 57-year-old man with fhe chietcomplainf of chewing difficulfy. In fhe maxilla teeth f 2,15, 16, t7, 22, 24,25, and 26 were missing and in the mandible teefh 37 and 47 were missing (Fédérafion Dentaire internationale tooth-numbering sysfem). The periodonfal condition of the remaining teefh was severely damaged, and there was remarkable mobilify. Ceptialogram analysis revealed 5 to 7 mm of loss ot vertical dimension caused by advanced attrition, with extreme crown wear to around 50% ot fhe tooth stnjctures. The occlusion and mandible moved anferiorly upward and bofh condyles displaced anferiorly The pattenf wore only a maxillary removable partial denfure with an overdosed sifuaficn. The f'eatment goals were to remove unfreafable pathology, resfore appearance, and creafe the besf possible health of the remaining tissue and masticafory sysfem. This pafienf would have been besf freated with a mandibularporcelain-fused-fo-metalfiKedparfial denfure fo créale a reasonable occlusal plane, and osseoinfegrated implants in fhe maxilla. However, the pafient refused any extraction ot his remaining teefh so the initial plah was unacceptable. We then sfarfed with reversible and less invasive procedures until the patienfs condifion and needs were more lully known. The sifuation was mainfained for more fhan to years, and exfreme cn^wn wear was freafed wifh a removable appliance. Opfimum care may nuf be the most expensive or complex. Treatment planning should be orienfed fo fhe patient's needs and denfal expectafions.

Comprehensive dentistry maybe better staged over several years, depending upon fhe patienf.

T. Walton, Sydney, Australia A Non-Glitzy Yet Uncompromising Restoration of a Disease-Debilitated Dentition The introduction ot preventafive measures has caused a dramafic reducfion in oral disease in AusfraNa, which unfil recenfly had one of the highesf DMFT rates in fhe world. However, such measures have also resulfed in a large percentage of the middle-aged population having severely debi I if afed yef relafively sfable dentifions For many of these patients fhe great advan tag es m techniques for both tooth- and implant-sjpported fixed prostheses are prohibited because of tina ncialcosf. The challenge tor us as prosthoctontists is fo dentally rehabilitate these people withouf compromising our goals for restorative dentistry. The rehabilifation of one such middle-aged woman who presented complaining of orofacial pain and whose dentifion was severely debilitated tollowing caries and periodontal disease will be presented, A comparison otcosf, maintenance requirements.

The Infemationál Journal of Pro5thodontits

450

and patienf evaluation ot oufcome over 10 years wifh a similar case restored wifh llxed tooth- and implant-supported proslheses will be given.

This case demonstiafes fhaf denfitions car tie ettecfively rehabililafed using relatively inexpensive techniques withouf compromising accepted goals tor restorative dentistry.

Focus Session B, Öwall, Copenhagen, Denmark Can We ver Bridges/fPDs Cantilever distal extension bridges have been used for many years and the results from bofh specialist clinics and general practice have been relafively well documenfed In summary, fhese haue shown fhat fhe periodcnfal fissues are able to withstand the load from such fixed partial dentures (FPD] well, fhough fhe risks of mechanical complications are high. The fypesotcompticafions and iheir origin, diagnosis, prevention, and treafment will be disoussed. In view ot the increasing possibilifies fo esfablish a lixed replacemenf with implant-supporfed FPDs, the freafmentoption with cantilever distal extension bridges no longer has fhe same importance as a restorative alfernafive. There are still several situations, however, in which it can be reasonable to use this fonn ot treatment, especially when the resulfs trom earlier clinical Studiesand experimental investigations are tat<en into conside raf ion during frealment planning. The modern use of canfilever disfal ejitension mandibular bridges will be exemplified and discussed.

J, Gunne, Un eä. Sweden Impiants The freatment ot the edentuious posferior mandible is offen a great challenge for the prosthodontist. Whether there is a subjecfive. objective, or bofh subjective and objective need for freafment, many opfions exisf When titanium implanfs were infroduced in fhe t970s and osseoinf eg ration was described, it was an innovation for treatment of the edenfulous jaw. t_ater sfudies also reported very successful resulfs ot implant freafmenf ot fhe partially edentulous patient. A sun/ey ot fhe literafure indicates a cumulafive sun/ival rate after 5 years of about 93%, The esthetic demands in fhe posterior mandible often have not been the highesf priorify However, fhe surgical and prosthefic profocol and fhe impianf components make it possible fo achieve a good eslhefic resulf. Offen the bone quantity and quality in the pgstenor mandible are reduced, and it is also a "high forces" region Consequenfly many nonevidenced biomechanicai recommendations have been proposed regarding the lengfh, number, diameter, and position of implants. In mosf cases the treestanding prosthesis is fhe first opfion of choice. Anatomic limitations could indicafe a foofh- and implant-supported prosthesis, which in some studies has proven fo be as successful as fhe treesfanding one. Impianf treatment in the posterior mandible is often a clinical application ot fhe shortened dental arch concept. No reports have indicated that fhis could cause problems. The biologic cost of

• 12.Numbers. 1999

International College ot Prosthodüntists

implan! Ireatmenl is minimal. Deleterious complications trom the placerrent of implants occ:ur very seldom and the biocompatibillty of both titanium and ceramics is exlremely good.

Alttiojgti more dala are needed about implants in the posterior mandible an ¡mplarl-supportefl prosthesis is a realistic treatment option J. Brudvik, R. Frank, Seattle, Washington The Modem Removable Partial Denture for the Postenor Edentuious Mandible A random sampling ol B2 subjects wearing mardibular Oass i and Class II removabie partial dentures was evaluated tor the relationship between Sie standards ot design and constnicBon. clinical acceptabilüy, and patient satisfaction. The results gave a significant correlation thai was unexpected and that can have a far-reatiiing etfect on ihe teaohing and practice of Ihis treatment modality. From this wide sampling of patients treated over the last E years, primarily by general dentists ¡n the Seattle area, only the number oí abutments rested, rest form, base Sïlension, and fü of the framework were related to gingivaLioral health. No support ivas found for any other design leatufe. None of the standanJs was statistically related to patient satisfaction with Iheir partial dentures The construction of the modem removable partial denture must therefere stress the 4 factors that actually affect health.

Abutment selecfion must be made relative to rests and guide planes rather than clasps and majoi connectors. Resl preparations should only be acceptable when they are positive and acute. effectively tying tooth and frame togettier but sSU allowing rotafion. The altered oase impressiori, taught in most dental schools, is seldom if ever usad in general practice. It is in fhe area of ttie fit olthefiamewori<that great progress is possible if trie clinician is willing to accept the responsibility of fitting the casting to the mouth insteaflofthecast The fit of the casting to the teeth can also be enhanced if more parallei guiding plane surfaces are cieated througti milling of the axial surfaces of abutment restorations, be tfiey crowns, bonded metal, or composite. The g/eat increase in frictional resistance to removal will allow a marked reduction in the number of ttesps, creatng much more esthetic partial dentures, finally, the addrton of posterior implant support for the partial denture will change the Class I and II dentures to Class IN and thereby eliminate many of the problems associated witii the postenor edentulous mandible.

current criteria for a healthy or physioiogic occlusion reflect this shin clearly Clinical observation, confimied by research findings, led tc the conclusion that the minimum number of teeth needed to satisfy functional and social demands varies individually and depends on a combination of predictable and less predictable factors.

Important factors are age, the (penodcntal) quality of remaining dentifion, the number and location of the teeth, the adaptive capacity, etc. The mam cbjective of thts paper is to contnbute to the discussion about the treatment ot the posterior edentuious mandible. In what situations is a shortened dentai arch an acceptable oral status in patients with a posterior edentulous mandible'' U. Lekholm, Göteborg, Sweden Possibililies and Limitations with Oral implants The use of oral implants in the treatment of postenor edentulous mandibles first began on a regular basis after the To rente rneeting in 19B2, at least wifh regard to the Brânemark implant system (Nobel Biocare) Consequently theclinical experience of such a treatment is today based on just over 15 years of practice. Over these years the original surgical protocol has been modified and adapted to the posterior jaw situation, and it has been proven fo be successful as sfudied in a prospective multicenter report after 10 years of follow-up. However, the posterior mandibular region may exert ditferenf clinical limifations and problems when placing implants because of anatomic characteristics such as jaw shape, bone quality, and inferior alveolar nerve location. The need foi a proper preoperafive examination and treatment planning IS therefore of utmost importance, with a carefully performed surgical technique, to achieve the desired treatment results. The principles ol the examination protocol, surgical handling, and possible treatment results will be addressed in fhe current overview presentation.

G. Buckley, Cork, Ireland The Evolving TreatmenlModaiities of Aasthetic Dentistry ¡or Maxiiiary Antenoi Teeth Extraction (with or wittiouf alveolectomy) of maxillary anterior teeth and placement of an immediate denture was once an acceptable treatment modality for improvement ot maxillary anterior tooth position and facial esthetics. Elective endodontics of maxillary anterior teefh and placement of retroclined post crcwns to avoid a removable prosthesis was an altemative treatment modality Tiiereafter, witti developments in orthodontic therapy and adhesive dental materials, oonversioncrowns, veneers, and adhesive fixed partial dentures were used as methods to restore the esthetics of maxillary anterior teetti. More recently the development of predictable implant systems (ad modum Brènemark) has added a further treatment modality fo restoring the esthetics of maxillary anterior teeth in adulfs. The evolution oi these treatment modalities is shown, particularly tiie acceptance now by adults of therapy involving orthodontics, dental implants, and prosthodonüos to restore dental esthetics

H. Choi, S. Shin. Seoul, Korea A Comparative Study on tne Fracture Strength and Marginai Fitness or Ihe Metal-Free FiberReinlorcsd Composite Bridge in Ihe Posterior Portion Fiber-reinforced composite (FRC) was developed to serve as a stnjclural component of denial appliances such as prosthodontic frameworks. A new FRC provides Ihe potential for fabrication of metai-free prosfheses with excellent estlietics. The purpose of this study was fo evaluate the fracture strength and the marginal fitness of FRC fixed partial dentures in the posterior region Sixteen bridges from each group, TargisWectris (Ivoclar), Sculptu re/Fibre Ko r (Jenenc), and In-Ceram (Vident), were fabricated. All specimens were cemented with Panavia 21 (Kuraray) on the master dies.

Strength evaluation was accomplished by using a universal testing machine (Instrcn). The marginal fitness test was measu/ed stereoscopically (50X). The fracture strength was significantly decreased for in-Ceram (23B.31 ± 82), Targis/Vectris {176.25 ± 18.93), and Scuipture/FibreKor{120.35±2D.08)bn"dges(P < 0.05). The FRC resin bridges were not completely fractured, white In-Ceram bridges were completely fractured in the pontic joint. The marginal accuracy was agnificantly decreased (or TargisaVectris (60.72 |im), Sculpture/FibreKor (73.10pm), and In-Ceram bridges(83.81 |Jml(P

W. Kalk, Groningen, The Netherlands Shortened Dental Arches The pnmary objective of dental care is maintaining a naturai functional dentition for lite, it is expecfedthafa growing groupoiaduits will keep their dentition into oid age. The traditional approach in prosthetic therapy was guided primanly by morphologic critena aimed at the preservation of complete dental arches, resulting in an emphasis on quantity in dental caie.

Noivadays, requirements such as esthetics and Functional comfort are considered more important. Although routine prosfhodonticcare wili stiil be important in the future, treatment strategy for (older) adulfs and eiderly people with a reduced dentition may require a dflerent approach. The

Voiume12; Number 5,199S

Fixed Prosthodonf tes

< D.01 ¡. The fitness of occiusal sites had a lower valuethan the maiginalsites ( P i 0.001), and the marginal gaps near the ponficweie greater than thoseof outer sites (P< 0.001). The results of this study suggest that metal-free FRC bridges are not suitable for clinical use in the posterior region, but are suitable for clinical use in shortspan bridges in the anterior region.

431

Theinternational journal of Pro^thodontics

International College of Prosthodontists

S. Fukuattima, Y. Shigela, Vokohama, Japan Fo*iv-up Study of Finea Bridges at Student Ciinic ot Tsutiimi University. Ten to Thirteen Years Alter insertion Ot the onginai group ot 302 patients who feceiued 3- or 4-urit tiled partiai dentures at the Student Ciinic ot Tsurumi University during the years 19B3 to 1936,102 patients with 10S fixed bridges attsnded tfie clinical examination after 10 to 13 years. The present addresses of 52% •t the rest of Ihe patients mere unknown, 40% deöined to attend, and 7% had died or were iii in Bed. During ttiese years 21 bridges were iost [failure rate ot 19 4%) and 9 nvere remade, in 30% of the abutment leetti periodontai probiems sucli as bleeding and/or pus discliarge dunng probing periodontai pockets were detected.

Therefore, this seemed to be the mcst serious problem to be solved. Of 154 abutment teeth, î 5 (9.7%) reveaied a periapical iesion v.tien examined radiographicaiiy, and 4 of these teeth 12.5%) were presumed vitai at the insertion, in 4.5% of aii abutment teeth secondaiy canes arDund crown margins and root surfaces was (ound Furthermore, patients mlio lost fixed bridges tended to lose more teeth [t>an those who retained the bridges fLI. Heners. W. Walttier. Karlsruhe. Germany Frequency and Risl< of Abutment Loss Aftei insertion oí Conical Crovun'Retained Bridges A longitudinai study was pertormed to observe ttie behavior of abutment teeth after incorporation of conioaJ crown-retained fixed partial dentures. The material comprises 1,326 patients with 7,470 abutment teeth that were treated during the period from 1980 to 19SB. In this paper the frequency and the risk of abutment ioss are evaluated and reported Aii cases were inciuded in a computer-based subsequent documentation system. Event analysis by use of the Kapian-fuieier method revealed that the probability of abutment sun/ival decreases to O.BS within an observation period ot 5 years and to 0.69 after 10 years. Further results indicate that the sun/ival rates of abutment teeth are strongiy dependent on the number of abutment teeth.

The influence of ciinioai findings sucli as probing depth, mobility, and vitaiity of Ihe abutments is also reported.

S, Lombardo. G. Audenir>D, F. Bassi, V. Previgljana. S. Carossa. Turin, Italy Specttomorphometric Evaiuation ot Light Transmission Through Aii-Ceramic Crowns on Teeth Reconstructed wilh Diflsrsnt Materiais The esthetics ot natural dentition is largely determined by the effect of incident iight. All-ceramic restorations offer the best appearance because they transmit iight optimally. On teeth that hare been endcdonticaliy treated the materiai used to rebuild the pin abutment must be considered from the esthetic standpoint. The aim of this sfudy was to evaluafe the influence ofdifferenttypes of pin abutment on iight transmission fhrough all-ceramic crowns. Three different natural teeth were used, each of which was reproduced with three types of restorations (IPS-Empress [Nobei Biccare) stained, iPS-

Empress stratified, and In-Ceram |Vident]), and reconstructed with four types of pin abutmenf {opaque gold alloy, pclished gold alloy, ceramicized metal alley, and all-ceramic) The natural teeth reproductions were each evaiuated by spectn^photometric analysis

cemented during a period of 14 months in patients who needed crown Iherapy The patients were selected from consecutive patients of the dental clinics involved in the study. The distribution of the bridges in the mouth, explained as the tooth replaced by the pontic. Is shown below:

S. Miyamoto, S. Mukal, S. Kukushlnia, Yokohama. Japan Foliow-up Study on Fixed Fartiai Dentures for Defects ot Upper Four incisors We reported on 50 cases of fixed partial dentures that had already beer inserted fcr defects of fhe 4 maxiiiary centrai incisors. We demonstrated the possibility that the defects be restored by means of fixed partial dentures if they are fabricated according to the foliowpng conditions: i l ' t h e ccclusal support index in posterior teeth is at least 9; and (2¡ the b.a ratio that shows fhe Oegree cf protnjsion of the free end is iess than 1.0. in this study, we fabricated new fixed partial dentures in consideration ofthe previous results and attempted tc identify fabricating conditions fcrthese defects Ihrough 10-year foliow-up. During tne years 1983 to 1968.14 of the bridges were inserted. Recall studies were performed after approximately 10 years. The foliow-up was carried out for 9 of 14 oases. The period of insertion was from 8 years. 2 months to 13years, 7 months {mean 10.1 years). For retainers, resin-facing crowns were used in 2 cases and p orce i ain-f used-to-metal crowns were used in 7 cases. Oniy both canines were used as abutment teeth in 6 cases, both canines and lirst premoiars were used in 2 cases, and 3 abutment teeth were used in one case. There were 11 vitai teeth and 12 endodonticaliy treated teeth. The b.a ratios were from 1.1 to 2.7 (mean 1 3), and the occlusal indices were from 9fo 12.

Although the 9 cases are stiii in sen/ice at present, 2 cases experienced some problems during fhis period. One was a fracture line on the porcelain pontic. and the other was disicdging from the abutment teeth. Ot the 9 cases foiIcwed up, 8 showed a satisfactory process, and the pcssibiiity of restoring the defects by rneans of fixed partial dentures was shown. The b:a ratio showing the degree of protrusion of the free end and the occiusal support index wouid be effective for designing the bridges.

A. Oden. K. A r v i d s o n . B. E n g q u i s t , L. Krystek-Ondraeek, D, fulagnusson. M. Molin.

J. Salo m on son. Huddinge, Sweden Procera AllCeram Bridges Densely sintered, high-purity aluminum oxide has been successfuilyciinically used for 9 years as a strong core materiai m Procera AiiCeram crowns {Nobei Biocare). A technique has been developed to produce Procera AllCeram fixed partiai dentures. These bridges are composed of a densely sintered, high-purity aluminum oxide framework that is combined with the dentai porceiain AiiCeram (Ducera Dental). The framework is made from single units such as copings to be cemented on prepared teeth and a centrai pontic. The copings are fused to the pcntic with a fusing matenai. The aim of this paper is fo report on the first ongoing clinical study of Procera AiiCeram 3-unit fixed partial dentures. The 40 bridges in ciinicai use were

The intemationii Journal of Prosthodonlics

452

Ma

Mandible

Total

Only bridges with perfect Tit were cemented.

They are evaluated at each point with the California Dentai Association's qu^ity assessment system. To date the results of thiscliricai study are promising.

S. Rinke. V. Schulz-Fincke, H. Schroder. F. Schäfers. A. Hüls, Gottingen, Germany Fracture Strength otMelsl-Fres Anterior ThreeUnit Fixed Partisi Dentures This in vitro study aims to evaluate fhe fracture strength of exfra-axially loaded 3-unif anterior fixed partial dentures (FPD) made of 3 different materials: A = In-Ceram (Vident); B = TargiWectris (Ivoclar); andC = Ribbcrd (Sigma Dentai Systems) + Artgiass (Kulzer). Aftar producing a metEdiic master modei of a 3-unit maxiiiary anterior fixed partial denture (righl central incisor fo canine) wifh a circular cutting depth of 1.0 mm (rounded inner shoulder), 36 v/orkirig models were made of Type IV gypsum; 12 identical FPD5 were produced with each system according to the manufacturers' guideiines After convenfional cenienfafion (In-Ceram: zinc phosphate cement) or adhesive lufing (other systems: Panavia 21 TC, Kuraray) of the FPDs on the master model, their fracture strength was tested in a universal testing machine (Zwick 1446. Zwick-Roel) with an extra-axial load application (30 degrees) at a crosshead speed of 1 mmimin. The following mean values of fracture strength were evaluated: A (In-Ceram) = 1.023 ± 102 N, B (Targis/Vectris) = 530 ± 90 N, andC (Ribbond) = 599 ± 68 N. Statistical analysis by analysis of variance and post-hcc comparisons (Tukey test) showed significantly higher values fcrthe convenliorally cemented Ir-Ceram FPDs than for the 2 adhesively iuted systems (Tukey test. P< 0.02). The fracture strength of the other specimens showed no significant differences (Tukey test B/C: F + 0.192); groups B and C formed a homogeneous subgroup. Even with adhesive lutihg the fracfure strength of the other specimens does not approach the fracture sfrengfh of all-ceramic FPDs. A clinically relevant difference in the stability of the other 2 systems could not be detennined. Because of its reduced fracture strength the application of anterior FPDs based on these materials shouid be iimited to iong-term provisional restorations.

! l 2 . Number 5,1999

International College of Prosthodontists

Removable Dentures E. Antonescu, lasl, Romania Tile Remoi/able Partial tDenluie—A Provisional or Tmnsäory Solution The provisional and/oi transitory removable parhai denture IRPD) influences all tissues of the stomatognattiic system m a mere complex way than a conventional fixed cr RPD that is considered permanent This is vïhy the designing and Building of such a denture rtiust be done at leastasiigorouslyasforapermanentone In this communication we present a special experience abcut the treatment of some clinical situatons in which the RPD was used as a provisional arWoi transitory denture. The clinical situabons that will be presented refer to a group of 58 patients (36 females and 22 maies) treated in ttiB Department of Prosthetic Dentistry of the Faculty of Stomatology in iasi, Romania. The i^PD was necessitated by bony substance loss subsequent to trauma (55%) or tumor extirpaton (34%).caused by hypodontia (10.5%), oras a complementary therapeutic solution forthe surgical therapy of cleft tip and palate {10.5°4) to permit functkinal recovery (mainly phonetic and esthetic).The prosthetic therapy differs acco'ding to tiie social ccnditons of the patient, and last but not least, according to the affective attitude ofthe patient toward the tooth loss and the denture type. Taking into consideration the possibifity ofthe supporting tis.sues in these classic situations, ngorous postprosthetic therapy is required.

T. Daher, Láveme, California Economical, Quality Complets PmcHcalTips

Dentures,

Asetotquairty dentures can be made easily if the patient ÊS presently wearing dentures. In the traditional way, we always start the process of denture fabrfcation by makjng a preliminary impression. Atlhoug h a lot of time was devoted to evaiuaïng exislng dentures, the patient's prostheses wiil be put asrde and the process ol denture fabrication is started f'cm "scratch" with ihe preliminary impressions. Even thougti many authors (Vig, Levin, Sprigg, Smith, etc) emphasized the importance ofthe use ot existing dentures in makirig complete dentures, we found ourselves still teaching cur students the traditioral way of making complete dentures. This presentation will focus on a practical, economical, predictable tectinique to make complete dentures. This technique can be used on patients needing new dentures or on patients unhappy with new dentures referred to you by general dentists. This presentation wiil focus on many pracicai tips, from the patient examination clinical visit, to impression making, to maxilbmandibular relations, to selecticn of teeth and Uieir arrangement, to flasking techniques and remount procedures, and finally to the postoperative treatments. The end result will be well-made dentures that are less costly and well accepted by patients. Fourclinicai appointments are necessary for their fabrication and two follow-up visits will suffice in general for any adjustments.

P, Flllpplnl, A- Fanti, C. Gandlnl. M. Allegil, Veroria, Italy In Vivo Evaluation of Chawing Efficiency ol a Wsiv Artificial Tooih in Patienis Treated with Removable Pariial Dentures

E. Mijlfitsky, Z. Ben-Ur, T. Bfosh, HamatHasharon, Israel Siiftness or Different Designs and CrassSeclions of Upper and Lower Maiar Connectors of Removable Partial Denluies

Removableprostheses have to guarantee such qualities as statiility and retention dunng function and support and preservation cf residual structures. Tc meet these requirements the realization of a stable occlusion is the most important factor. Different kinds of artificial teeth have been studied to prevent occiusal prematurities and interferences dunng function. However, the chewing effciency (CE) of these prosthetic elements IS iow because cf the reduction of tiie occiusai lable and the poor inclination of cuspai slopes. Furtheimore, in partialedenlulismthese artificial teeth show a poor esthetic and functional integration with the residual dentition In such clinLcai situations the use of an anatomic artificial looth may be advantageous. We evaluated the CË ol a new anatomic artificial tooth (SR-Postaris, Ivoclar) incompanson with asemianatomic one {Orthotyp, Ivoclar), in a group of 8 partially edentulous patients treated by means of removable partial prostrieses (RPD). To guarantee the homogeneity of the population each patient was provided with 2 prostheses that were identical except tor the artificial teeth employed. We tcliowed a standard expérimentai procedure introduced byOlthotf in t9B4. »consisted of the execution of 10,20,40, and 60 masticatory cycles with a test food {Optosii cubes, Bayer) in basal condition (le, without prostheses) and with the 2 RPDs. The tesi was performed 1 week after the application ot the prostheses (t0) and 3 months latei (t-1 ) for each prosthesis The statistical evaluation of ccilected data showed an initially poor CE of Postaris in comparison to Orthoiyp (1-0). in the 1-1 tests, however, the performances of Ihe Z artificial teeth were almost identical. Moreover, an extrapolation of our data suggested a further improvement ol Pcstaris after 3 months of function, which was not found for Orthdtyp

Major connectors of removable partiai dentures must dislribule forces biiaterally without damaging the supporting tissues. Til is sludy attempts to investigate which design and cross-secticnal shape of majorconnectors most favorabiy influence ngidily and llexibility. Five designs for maxillary removabie partial denture major connectors and five lingual bar major connectors ol different cross sections were cast in chrome cobalt alloy on a master model. Points M and P. 20 mm apart on the casting, representedthe position of the first piemoiar and second molar teeth.

Vertical and horfiontai forces were applied to each point whiie tfie opposite side was gripped in an Instron testing machine. A force-defiecling cun/e was obtained for each point of loading.

Meanstiffness values were obtained for loading in compression and torsion. The values for toisional loading simulating vertical forces were lower when compared to values obtained for compression loading that simulated horizontai ccclusai forces. Differences in sfiffness were greater in lower major connectors loaded at M and P. The half pear-shaped cross section was found to be the stitfest. In the upper connector the most rigid major connector was found to be the anterior-posterior paiatal Oar combination placedondifferenthonjontalandverlicai planes.

The most fiexible was the U-shaped design, in the iower connector the most important factor in achievingngiditywasfoundtobethecross-sectional shape of major con neciors. The ha if pearshaped cross section proved to be the most rigid. For maximum stiffness the upper major connector shouid cross the maxilla opposite the edenluicus area anteriorly and posteriorly in dilferent planes, and arch length should be as short as possible and compensate for limited height by increased thickness of the half pear-shaped ma|orconnectorinthe lower connector

J. Koumjian, San Francisco, Calitornia •Deniure LoolC Versus 'Nalural Look'

B. Roberts, Westmead, Sydney, Australia Ttie Longevity or Kennedy Class I Metal Partial Dentures

Today's patients are more estheticaiiy conscious and influenced by mass media. They are concerned not only with their health, but also with their appearance. The unnatural and conventional tooth arrangements and gingival contours seen in the mouths of many deniure wearers draw attention to Ihe falseness of their teeth. Esthetics in complete denture construction could be defined as the creation of lifelike prostheses that restore the patient's individuality and appearance. The denture base greatly influences the esthetic outcome. There is no clear-cut formuia for achieving successful results. Therelore, foiiowing some of the guidelines discussed in this presentation will help the dentisL in fuifiiiing the responsibrlity to create a natural and esthetic resuit.

Volume12, Number 5, 1999

453

This paper brings together studies of Kennedy Class I metal partial dentures made in 3 environments: the University of Otago Schooi of Dentistry, Dunedin, New Zealand, Westmead Oral Health Centre, Sydney, Auslraiia: and a specialist practice in Sydney. Australia. In a study of 101 subjects, 28 wore their dentures constantly, 14 removed them at night, 31 wore them sporadically, and 28 never wore the denture. Of Ihe 28 never-wom dentures, 23 were discarded within t year of issue. The Russell Periodontai index of abutment teeth was significantly higher ( P t 0.01) than for nonabutment teeth, but the Pi ofdenture wearers did not significantly differ from nonwearers. When cornpan ng results from the 3 studies to determine it socioeconomic status made any difference to the success of denture wearing, there was no significant difference and it was found that patients manage well with shortened dental arches.

The International Journal of Prosthodontics

internationai ColleEe ot Prosthodontists

H. Wenz, K. Herframpf, K. L e h m a r i n , t^arburg, Germany Clinical Longevity ot Removabie Partial Dentures Retained by Telescopic Clowns witb Clearance Fit Sincetheywerefirstdescribed in 1B8S by Starr, telescopic crowns have proven an eflectivs means of retaining removabie partial dentures [RPDj. Contrary to other telescopic or doubiecrown systems, doubie ciowns with clearance tit can be used to retain bofh tooth- and mucosasupported RPDs. A retrospective chart review was conducted on 111 RPDs inserted between 1SB4 and 1996. Doubie crowns with clearance fit were used as retainers, including an exchangeable attachment (TC-Snap) for retention.

The framework, including the outer crowns, was cast in one piece in a Co-Cr atloy without any soldering or weiding. The rigidity of the base-mefai alioyenablesadesign ofthe prostheses wittiout major or minor connectors. The marginai periodontium of the abutrnent teeth was not covered by the denlure base. The mean age of the patients at the time of insertion was 57.5 years [standard deviation ± 12.3 years; range 18 to 31 yearsj.The mean numberofdoubte crowns per denture was 3.53 ± 2 13 (range 1 to 9) The mean oftservalion period of the dentures was 3.4 ± 3.4 years (range 12 SyearstoSmonths) Loss of abutment feeth, fracfure of the framework, and endodcntic treafment after insertion were invesfigaled. The sureivai estimation of Kapian and Meier was used fc evaluate the survival probability of dentures and abufmenf teeth. The probability of having lost aii abutment teelh was 3.3% after 5 and 1Û years. The probabiiity of having kept ali abutment teeth 5 years after insertion was 86.9%; lOyears after insertion It was BO.2%.

The survivai probability of an abutment tooth (double crown with ciearance tit] was 92.5% after 5 years and 89.4% after 10 years (n - 392).

No significanf diftersnces in suivival prcbabiiity were tound for abutment feeth of tooth/toofhmucosa supported dentures and puieiy mucosasupported dentures. The resuits wiii be discussed wüh the outcomes of ofher studies

Dental Materials D. Gugiielmino, F. BassI, P. Pera, L. Paracchini, G. Schierano, Ispra, Italy Chemical Corrosion to NaF of Some Dental Metal Alloys Fluoride is widely used in dentistry as prophylaxis, in removabie partial dentures (RPD) the écologie changes are such fhaf correct orai hygiene and the use of fluoride are quite important, in the iiterature studies about tiuoride corrosion on metal alloys, especiaiiy on titanium, are not numerous or conclusive. The aim of fhis sfudy was fo evaluate the behavior of the principal metal alioys used in RPDs in the presence of fluoride. Eighteen specimens of the same shape and dimension (11 .Scm^) inTi, CoCr, and CoCr overcoaied with TiN v/ere tested in 2 solutions: artificial saiiva (Fusayama-tulayer) and fhe same artiticiai saliva wifh NaF 0.2% for a period of 4 weeks at a temperature ot 37.5°C. Corrosion was evaluated by anaiyzing ionic reiease on

programmed drawings by mass spectrometryot inductiveiy coupled piasmas.The CoCrwas not sensibie to fluoride (0.0075 ppm/cm' us 0.0047 ppm/cm^ for Co); Ti underwent a very low corrosion in fhe soiufion with NaF (0.034 ppm/cm^ vs 0.OÛO1 ppm/cm^ for Ti), probabiy without clinical relevance, and TiN underwentthe highest conosion (9.36 ppnVcm^vsO.O0O5ppnVcm= tor Ti) P. K a m p o s i o r a , A. A n t o n o p o u l o s , A. Doukoudakis, 5. Bayhe, G. Papavasiliou, Athens, Greece Strain Gauge Stress Distribution Analysis m Denial Cements for Full-CoversgE Crowns Dentai cements are relativeiy brittie materials. It they are strained over their eiastic iimitf hey wiii break. If masticatory forces on compiefe-coverage crowns cause siress concentration in fhe cement thaf exceeds ifs eiastic iimif, microfractures wiii occui. The purpose of this study was to use strain gauges for measurement of stress developing in the luting cement at the borders of complete-coverage crowns made from Type lil gold aiioy. Four cements were used' zinc-phosphafe. poiycartraxyiate, giass-ionomer, and composife resin cement. The secondary purpose of thestudy was to compare the resuits with fhose from simiiar modeis anaiyzed by finite element anaiy&is To ioad fhe models an instron machine was used, and for the anaiysis s personal compufei through a Daq-Book apparatus was used Twelve modeis with naturai mandibular premoiarswereccnstructed. The teeth covered with crowns made from Type i it goid atioy were surrounded by artificia i periodo ntat iigamcnt.

Croivns were iuted with the cements menlioned above (fhiee modeis for each cement). Strain gauges were piaced on the facial and iinguai surfaces of the models, utiich ivere then ioaded with 10 tul Fa axiai and obiique (12 degrees) pressure.

Statistical anaiysis of resuits was done by repeated-measure anaiysis of variance. From the resuits stress concentration values were low for ali models. Zinc-phosphate cement developed higher stress ooncentiations, in a statisticaily significant dagiee, compared to fhe other three cements. Aiso statisficaliy significanf were differences among stress vaiues from axiai versus obiique ioading. Under axial ioading more stress was concentrated on the faciai gauges, while the opposite was true for oblique loading. Stress concentration in cements at the borders of compiete-ooverage crowns under normai masticatory pressure is very low. Zinc-phosphate presents the worst behavior compared to the other cements. Stress vaiues under oblique ioading were ten times greater than fhose under axial ioading, this shouid be taken into consideration when making compiete-ooverage crowns.

S, Kim, B. Song, S. Oh, T. Jin, J . Dong, Iksan, JeonBuk, South Korea Properties of Reused IPS-Empress Ceramics iPS-Empressceramic (Nobei Biocare) is widely used in clinics because of ifs high sfrength and good esthetics, but it costs more than other restorative matetiais. Reused ceramic ingots can cut costs. The purpose of this sfudy was to estimate the vlabiiity of reused IPS-Empress ceramics in ciinicai appiioations. Properties such

ationai lournal of Prosthodontit

454

as pressing accuracy, coior sfabilify, flexure strength, wear resistance, and microsfructurai change were estimated tor newiy pressed ingots, ingots reused after a second pressing, and ingots reused after a third pressing. There were no statisfical differences in pressing accuracy, coior stability, and flexure sfrength of the difterent ingots. However, fhe wear resistance of fhe ingots pressed 3 times was ipwer than that of ingots pressed once or twice. Microciacks inside fhe ieucite crystai and around the glass mafrix were oieariy observed in ingots pressed 3 limes, if is ciinicai iy acceptable to use ingots that have been repressed once, but nof fhose that have been pressed 3 times.

P. M i l l e d i n g , A. P e r s s o n , A. Oden, Göteborg, Sweden Influence ot the Color of Procera AilCeram Core Materiai on the Final Color ot the Crown ProGeraAiiCeiamcrowna (Nobel Biocare) contain a core maferiai with one color made from densely sinfered, high-punfy aluminum oxide and fhe veneenng porcelain AliCeram(Ducera).

The base kit ot this porcelain contains sixteen Vif a shades of opaque iiner, sixteen shades ot dentin, andan incisai seL The aim of this study was to evaluate how differences in color of fhe core maferiai influence the color of the final crown. Thirty-four aiuminum-oxide disks were manufactured wifh a diameter ot 11 mm and a thickness oiose to 0.6 mm, which is fhe thickness of a Procera AiiCeram coping. Sevenfeen disks were made darker and seventeen were made lighter than ordinary Procera AiiCeram copings, and sixteen opaque iiner shades were fired on the two types of disks Sixteen dentin shades were fired twice and finally a layer of glaze was appiied. giving disks with a mean thicknessof 1.72 mm. The CiEL-s-B-coior coordinates we re determined using a colorimeter (tuiinolta Spectrophotomefer CM-503Í) with the disks piaced on a white calibrafion plate before tiring the porcelain and after every firing moment. The resuits were analyzed by oaicuiafing the color ditterence i E = (AL')2 -i- (Aa')2 -t (AB')2 before firing porcelain and atter every moment The mean vaiues and standard deviation of AE and the mean values of fhe thickness otthe disks (in mm] after every procedure step are shown below AljOj Opaque +0.62 17.6 ±1.7

+Ö'i4 2.3

o'M 1.4 1:07

-0.3S 098 ±0.6

-0.08 1.26 ±0.7

+0.0 J 1.38 ±0.6

The AE values of the final disks have values fhat make it difticuit to observe any visual difference in coior. it is possibie to use one coior forthe core materiai since fhe opaque iiners give fhe copings the desired coior.

A. Moormann, L. Wehnert, W. Freesmeyer, C. Knabe. R. Radlanski, Berlin, Germany Influence ot Surface Conditioning by Ion Implantation on the Bond Strength of Goid Alleys and Porcelain The aim of the present stucfy was fo investigate the influence ofthe surface conditioning ion im-

• 12, Numbers, 1999

International College of Proslhodontists

plantation process on a mefal-porcelain tjond. In tdecaseofporcelain-veneered titanium, ion implarfation avoids decreasing bond sfrenglh afler artificial aging by thermocyding. Therefore, higheneigy silicon ions are implanted info the tifanium surface prior fo fhe porcelain finng process. Tfie hypothesis Biaf these results can be extended to other mefal-porceiain combinafions was fesfed in this study. Two high-noble metal alloys (Degudent U/Degunonn, Degussa! were veneered with one convenfional and one low-fusing po/celain (Duceram/Duceragoid, Degussa! and fesfed for tfie bond sfrengfh of fhe porcelain with fhe fhr^e-poinf bending fest according fo Schvirickerafh. For half of fhe test series si I iconion implantation was applied prior to the porcelain tiring process and compared to a non-ion implanted senes. Artificial aging was achieved by therrmccyclmg wifh 20,000 femperafure changes and compared fo a series without thermocycling. In contrast to conventional titaniumporeelain systems fhere was no loss of bond strerigfh after thermocycling in fhe case ot the porcelain-veneered high-noble alloys used in fhis investigafion For fhe Degunonn alloy veneered with ttie low-fusing porcelain Ducer^gold tfie bonct-strength values increased slightly when tfie specimens were conditioned by ion implanBtioh Two-way analysis oí vanance showed fhat these differences are statisfically significanf.

Ttie bond strength of Degudenf U wrth Du ce ram increased by 59% if fhe mefal was implanted vnfh siHcxin ions. The resutfs show fhat fhe lon-impiantaüon process is suifable to increase fhe bond strength ot high-noble alloys with conventional and wifh low-fusing porcelains.

The development work presently being undertalien aims fo improve fhe accuracy of fif and weight reduction in denfal prostheses through Lhe application of superplasfic-forming fechniques on Ti-6A1-4V alloy Feasibility sfudies were initially undertaken using a large indusfrial forming machine These studies gave encouraging results and were followed by the design and manufacture of a superplasfic former capable of produong smaller componenfs for dental applications mote economically. Previous work had been undertaken on the superplasfic forming of complete denture bases in Japan (Ifo M. etal, 1989!. However, Ihe initial impetus for the work ot our group was fhe producfion of a beam tor an implant supersfrucfure The perception was fhaf fhe elimination ot fhe lost-wax casting process in the producfion of a gold beam, by forming a fjtanium alloy beam directly onfo a die, would reduce fhe sources of potential errors of ff A variety of components for conventional prosfheses and surgical procedures have now been formed. Cur renf research is directed af fhe improvement of ceramic die materials and the bonding of materials to fifanium alloy bases. The capifal cosfs involved in seffing up the production ot componenfs for denfal prosfheses by supeiplasflc forming are high.

However, the potential for sfrengfh, lighfness, and accuracy of fit conferred on prostheses and fhe design enhancement fhal fhe method affords fo denfal technology make the financial cfiallenge worfh meefing.

J, Nissan, B, Lauter, T, Brosh, D, Assit, Tel Aviv, Israel Accuracy 0) Polyvinyl Siloxane Impressions— Effect oí Impression Technique

M, W i c h m a n n , K, K a r a u , Hannover, Germany Retention and Wear ol Precision Attachments

Tliereismuch discussion in ttie dental literature regarding the effect of impression fechnique on the accuracy ot cast resforafions The purpose of this sfudy was to assess the accuracy of3 widely used impression fechhiques (onestep, 2-step, and polyefhylene spacer), using the same impression material ¡polyvinyl siloxane) in a laboratory model. For each technique tömpressions were made ot a sfainless sfeel master model containing 3 compiefe crown abutment préparations, which were used as the posilve control. Accuracy was assessed by measunng 6 dimensions (intra- and interabutmenf) on stone dies poured from impressions offhernastermodet One-way analysis of variance showed sfaSsficallysignificart differences among fhe3 impression techniques for all infraandinterabufment measuremenfs (P< 0.001 ).

The overall discrepancies of the 2-step impression technique were signiticanily smaller than in the one-step and polyefhylene impression techniques. The 2-step impression fechnique, wrih controlled bulk wash, is the mosf accurate for fabricafing stone dies, J, Walter, R, C u r t i s , A, J u s z o ï y k , P, Likeman, London, United Kingdom Appiications of Superpiasiic Forming in Dentistry

The work is supported by the Special Tnjstees oí Guy's Hospifal and The Royal Society.

Precision attachments are commonly used to connect removable partial denfur^s to abutment feefh, Tiie aim of fhis laboratory study was fo measure to whaf exfenf wear between matnx and patrixdepends on thefype of alloy used for manutacfuring the aftachments. In a comparative sfudy we subjecfed mfracoronal precision attachmenfs fo alfemafing load cycles in a wear simulafor. The Duolock affachmenf (Microdenf) was selected for testing because matnx andpatrix are available in diííerenf precious alloys [Mainbond EH, Plafinilridium 80/20, Alba O, and Heraplat, Kulier! as well as fifanium (grade 2/99.7), For our fesfing we seiecfed fwo different combinafions of precious alloys recommended by fhe manufacfurer (Mainbond EH with Heraplaf and Alba O wifh Platin/lridium 80/20! as well as the combination fitanium matrix wih titanium patrix. Six specimens of each attachment were subjected fo the wear fesfs, Tliese consisted of a fofal of four consecutive cycles of 10,000 separafing and pining movemenfs starfing at a retentive torce level of 7 N. Affer every fen cycles the maximum torce needed fo separafe maf rix and patrix was measured and sfored. The attachmenfs made from titanium showed a ccmplefe loss of retenfive forces during fhe firsf 1,000 loading cycles. After acfivafion, consecutive loading cycles showed Idenficai results. In comparison, atfer 10,000 loading cycles fhe retentive torces oí fhe aftachments made from precious alloys mainly

Volume12,Number5,1999

455

consisting of gold and platinum (Maihbond EH, Heraplat) showed only a slight decrease, from 7 lo 5.5 N. The combination mafnx and patrix made from precious alloys mainly consisfing of plafinum, palladium, and only a small quantity of gold [Alba O, Plafin/lridium 80/20! showed a sudden and unccntrolled increase of frielion fo values of more fhan 40 N, resulfing in complete locking befiveen mafrix and pafrix Our results indicate fhaf fhe type of alloy used for manufacturing precision attachments plays an important role in their frictional behauior under simulated clinical function. Precious alloys consisfing mainly ot gold showed Ihe mosf constant retenfive forces and fhe smallest amount of wear, D, Yoon, S, Shin, Seoul, Korea Bond Strength of Reintorced Composite Resins to Dental Alloys

indirect

This study was undertaken fo evaluate fhe shear bond sfrength of fhe reinforced indireot composite resins fo denfal alloys. Three different composife resin systems [Artglass, Kulzer; Sculpfure, Jeneric. and Targis, Ivoclar! and ceramic [Vifa VMK 68, Vident! were bonded to NiCr-Be alloy (Reiillium III, Jeneric! and gold alloy (Deva 4). Shear bond strength testing was carried out using a universal fesfing machine and de bonding surfaces were examined using a sterosccpe and scanning elecfron microscopy. The shear bond strength ot reinfcrcsd indirecf composite resins fo denfal alloy was approximafely half fhaf oí ceramic to denfal alloys (P '- 0,01 ). There was no significant difference in the shear bond strengfh among the reinforced indirect composife resins (P<0.05).

Type of alloy did not affecf fhe bond sfrengfh oí resin fo mefal. but the shear bond sfrengfh of ceramic fo gold alloy was higher than fhat oí ceramic fo Ni-Cr-Be alloy (P< 0.05) Sculpture showed cohesive, adhesive, and mixed failure modes, buf Artglass and Targis showed adhesive and mixed failures Ceramic showed cohesive and mixed failures.

General Prosthodontics B. Bergendal, Jon ko ping, Sweden A Ouestionnaire Survey on Tcolh Agenesis in Patients with Hypohidrotic Ectodermal Dysplasia in the Nordic Countries As preparatory work tor fhe 7th consensus conference alfhe Insfitute for Posfgraduafe Denfal Education in Jönköping, Sweden an ini/enfory of patients wilh a fenfative diagnosis of hypohid rofic ectodermal dysplasia (Christ-SiemensTouraine syndrome, EDA) was made. EDA is the most common of fhe ecfodermal dysplasia syndromes and is characferized by hypoplasia oí hair, feefh, sweaf glands, salivary glands, and symptoms irom other organs of ectodermal origin EOA isa rare disorder with an estimated incidence of 1 in 100,000 births. The aim of fhe sfudy was to infeiview EDA patienfs of specialisfclinicsindentisfrylnthe Mordlc countries and assess foofh agenesis in this group ot individuals. Specialists in orfhodontics, pédiatrie denfisfry, and proslhcdonfics were asked fo repori age, gender, and number of tooth agenesis

The International Journal oí Prosthodontic

Internationai College oí Prosthodontists

occurrences ih patients with a tehtative diagnosis of EDA syndrome. Reports on 179 patients were collected. Their age ranged from 2 io 73 years. The majority of the patients were children and young adults; only 24 individuals (13%) weie 25 years or older. Of the reported patients, 70% were male (125 men and 54 women). In 167 patients radiographie eiaminafion was performed—fhis constituted the basis for diagnosis of agenesis of teeth The number of tooth agenesis occurrences varied from 0 fo 28 with a mean of 15.3. Anodontia in bofh jaws was seen in 7 patients. Tooth agenesis was seen in ail types of teeth. The teeth least frequently affected were the maxillary central incisors, tollowed by the maxillary first molars, [f was concluded that this inventory reveals a substantial underdiagnosis of EDA syndrome, especially in adults, and that diagnostic criteria need to be established foi diagnosis.

The resuits of the consensus conference have been published: Bergendal B, Koch G, Kurol J, Wanndahl G Consensus Conference on EctodermalDysplasia with Special Reference to Dental Treatment. 1998, Stockholm, Sweden.

A. Jokstad, Oslo, Norway An Appraisal ol the Papers inlUe International Journal of Prosthodontics Evidence of the effectiveness of therapeutic interventions depends on study design. The best evidence is based on randomized controlled trials c]f appropriate size in a lelevanl clinical setting (Richards D and Lawrence A, 1995]. The aim of the present review was fo appraise the papers published in an influential refereed journal in prosthetic dentistry. All 728 papers published in the UP were reviewed and categonzed acx:ording to study design, clinical problem, andprosthodoniicsubtopic Authors'addresses and, when appropriate, the sample size and obsen/ation period were also reported. The variables were cross-tabulated to elucidate possible relationships. The iJP included papers on fixed (n = 230), removable (n = 158). implant (n = 117), and general prosthodontics {n = 107), oral function (n = 57), general denfistry (n = 36), and maxillofaoial prosfhefios (n = 21). The majority were laboratory studies (n = 404), many with emphasis on new materials and products.

A relatively large numbei of review and descriptive articles was identified (n = 156). The mosf common aim in the ciinicai studies (n = 166) was reporting prosthesis prognoses; 9 were randomized controlled trials There was little focus on validating treatment outcomes in cohort, case-controlled, and cross-sectional clinical studies Considerable resources in prosthodontic research are allocated to studies v/ifhiittleevidence for documenting therapeutic benefits of clinical prosthodontto treatment G. J ö n s s o n , L. Sandahl, T. Nordin, P. Hising, P. Nelvig, Sundsvall, Sweden Evaiuation ot the Clinical Use alihe Sterngold One-Piece Abutments Nonhexed one-piece abutments (Sterngold) are thought to be advantageous to prevent bacterial leakage. The present study reports the clinical use of Ihese one-piece abutments in implant

rehabilitation Atotalof44 consecutive patients had 234 implants placed using standard techniques. After a healing period of 3 and 6 months in the mandible and maxilla, respectively, 158 one-piece standard (ABS) and 56 conical (LAB) abutments were installed. The prosthetic procedure toliowed tha standards for the BränemarK-type implant system. One year affer loading the implants the bridges were disconnected and a clinical examination was performed. Ttie results showed that 5 implants were lost in association with abufment connection. Of fhe 228 impiants »lat were stable at that time 7 (3%) had been lost in the maxilla at the 1 -year control. Removal of the bridges at the 1 year cohtrol showed no rotational movements of ihe abutmenfs and no tightening was needed.

Abutment complications were reported for one patient. Radiographic examination of the marginal bone level showed a mean bone level reduction of 0.3 mm during the first year of loading Evaluation of the marginal tissue reaction at the 1-yea(control showed a clinicaliy healthy gingiva for 9 1 % of the patients, and the remaining 9% showed a slight redness and/or swelling of the gingiva No periimplantitis was identified. The results in the present study represent ihe 1-year results within a 5-year study.

These preliminary results also indroaied ihaf the simplified design of the Sterngold nonhexed one-piece standard and conical abutments macJe insertion quick and easy The resuits support the use of the Sterngold one-piece design as a reliable abutment alternative in the clinic.

M. KfonStröm, S, Palmqvist, B. Söderieldt, Skövde, Sweden Prosthodontic Decision Maidng Among General Dentists in Sweden: The Choice Between Crown Ttierspy and Filling The aim of this study was to analyze dentists' evaluation of factors related to fha choice between filling arHj crown therapy and to determine whether these evaluations can be explained by social and demographic attributes, job situation, and attitudes. Questionnaires were sent to a random sample of 2,059 Swedish denfists. The response rate was 76% (1,567 dentists). Private practitioners accounted for 50% of ihe respondents and 50% were publicly employed; 58% were male and 42% were female dentists, in the questionnaire tlie choice between filling and crown fherapy in a clinical situation was presented. The dentists were asked to marie their assessment of the relative importance of 14 different factors on a visual analogue scale (VAS). fiflulfiple regression was rijn for all 14 ifems as dependent variables using scx:ial and demographic attributes, job situation, and attitudes as independent variables. Large individual variations in opinion were seen among the dentists regarding the importa nee of the various patient-related factors. No data reduction was possible using principal component analysis. Dentist-related factors (social and demographic attributes, job situation, and attitudes) explained little of the variations. The items rated as the most important were "patient's wish" and "treatment prognosis," and the items rated as ieast important were 'treatment time required'' and "number of visits required for treatment." The differences between groups were small, ior nc item exceeding 0.7

The Internationai journal of Prosthodontic

456

step on the B-grade VAS. The study showed a great variation among individual dentists.

However, the dentist-related factors explained iittie of the variance Only minor differences were seen between groups of dentists. No data re. duction was possible, indicating that the questionnaire instrument used here did fully capture the factors that really influence the treatment choice between a filling and an artificial crown.

S. Palmqvist, M. Kronström, B. Söderfeldt, Kokkedsl, Denmari* Prosthodonlic Decision Making Among Gênerai Dentists in Sweden. II: The Choice Between Fixed and Removable Partial Dentures This paper is part of a comprehensive study of prosthodontic decision making among Swedish general dentists using questionnaires sent to a random sample of 2.059 individuals. The participants were asked !o evaluate by means of visual analogue scales (VAS) the importance of a series of patienf-relafed items for the choice between a fixed pariiai denture and a removable partial denture. The variables "patient's wish," "prognosis of the treatment," and "conditions of possible abutment teeth" were given the higiiest ranks; the variables "time required for treatment' and "number of visits necessary for treatment' were given the lowest ranks, but there were great differences among individual dentists in their evaluations. Using principle ccmponenf analysis the items were reduced lo 3 factors; time, health, and comfoit. These factors were ruri as dependent vanables in multiple regression analyses with dentist-related factors (social and demographic attitudes, job situation, and attitudes) as independent variables. The most striking significant differences were noted between publicly employed dentists and private practitioners regarding the importance of the health factor. Dentists' attitudes were significantly associated with the comicrt factor. However, Ihe models explained only a few percentage points (up to 7%) of the variation. The results imply that otrier variabies, suoh as personality traits that cannot easily be captured by means of a ques.. tionnaire, probably are responsible for most of the variations in ihe dentisfs' evaluations of the importance of various patient-related factors.

C. Taddei, H\.Me\z. Strasbourg. France Resoiution ot DiHicuit Cases in Complete Denture Prostheses The success of prosthetic treatment in edentulous patients depends mainly on 2 factors: restoration of function and psyohologio acceptance of the prosthesis by the patient. Function can be judged objectiveiy by comfort, which is directly linked !o denture retention and stabilization, but also by masficatory efficiency, incision, esthetics, and affective factors. The difficulty of a given case can be evaluated according to these criteria. A case can become difficuit when anatomic and physiologic ccnditions are unfavorable, especially when the alveolar ridge shows deep résorption Difficulty can also appear in a normal anatomic context when fhe paiienf refuses the denture, when they do not wear it, or in the particular case of shifting to total edentulism This presentation wili address

Volume 12. Numbers, 1999

International College of Prosthodontists

particularly fhe functional difficulties when deaiingwith mandibuiar and maxiilaiv complete dentures. In these cases traditional treatments are limited by the reduction of the supporting area and rrodiflcations of the anatomic environment.

Stabilization and retention can prove insufficient despite a well-managed treatment Hence, retaining nMts can be a positive aitemative to solve some of these difficulties. The use of osseointegrated impiants unveiis new opportunities for therapeutic solutions. This IS now a weiiknown tectinique that enables patients to recover good masticatory function. In mandibular and maxfliary resection after an oncclogic treatment these techniques prove to be very efficient.

W.Watther. M, Heners. Karlsruhe. Germany Clinical Data as Knowiedge Basis tor Prosthodontic Treatment Pianning and Ouaiity Assurance Unf I today few efforts tiave been made to make dertaldocumentationappiicabie for ciinicai purposes. One approach is the subsequent documentation system, which has been under contnuous deveiopment by the Gennan Academy for Advanced Dentai Education Karlsruhe since the mid 19aOs. Ciinicai information about dentalffierapyand its sequelae is reconJed by this system. Furthermore, it allows one to evaluate ciinical data to support clinical decision making.

The first aim of dental treatment plannjng should be the definition of an individuaiized prognosis at the moment of treatment decision. The computer offers significant support in this area By processing the recorded information for this question, ie, the probability of iong-temi success. Treatment pianning the longevity of a dentai restoration is of special relevance in assessing the quality cf dental therapy. The empincal knowledge Basis of the subsequent aocumentaton contains all infomiation needed to conduct time-related estimation rates, suchas the Kaplan-Meier statistic. In this way the denfist gets an insight into Ihe iong-term results of fiis or her therapy. The system offers the opporlunty to implement advanced statistical methods for intemal quality assurance in the tJental pracbce.

Meet the Future: Information Technology S. Koch, Uppsala. Sweden £tteaive and Quality-Controiied Use oi Digital Radiography in Prosthodontics During the few last years fhe number of commerciaiiy available digital radrcgraphic systems has increased rapidiy. But do they reaily allow for Bvetyday use of digital radiography in dentai praclice today? This paper will discuss advantages and disadvantages ol conventionai radiography and how the introduction of digital radiography in the dental practice affects clinical *orl(. The presentation compnses the effective andquality-controlieduseofdigitai radiographie systems in prosthodontics, cognitive ergonomie aspects with regard to design and retrievai in

image databases, advantages and disadvantages ol using image-enhancement routines during diagnostic interpretation, and the use of decision-supportsystems tor diagnosis and therapy, in particuiar. the possibilities and limitations of digital image manipuiation. considered to be one of Ihe mam advantages of digitai radiographœ systems, are discussed more in detail Exampies for quality-contrclied use ot image manipuiation methods that are adapted to the ciinicai requirements in prosthodontics wiii be presented B. Kordass, S. Seipel. I. Wagner, Uppsala, Sweden Trie Virtual Articuiator—A New Chaiienge in Prosthodontics?

Virtual reality technology is one of tne most important innovations for research, deveiopmenf, and industrial production. In dentistry virtual reality technology wiii be useful to provide better educafion by simulafior as weil as to enhance working procedures that conventionaiiy are limited, eg, fhe mechanical articuiator It is the purpose of this paper to present a concept and strategies for the future replacement of me mechanioai articuiator by a virtual ore. This virtual articuiator wiii signficantiy reduce the imitations of the mechanical articulatoiand, a</ simulation of reai palient data, aiiow for anaiyses with regard to static and dyramrc occlusion as weii as to jaw reiation Tne main topics of the presentation are' ¡1) impiementation of fhe virtual articuiator with digitized maxillary and mandibuiar models; (2) matching computer-aided registrations ot ¡aw movements with the jaw modeis; (3) visuaiizaticn of unusual views on dynamic patterns cf occiusion: and (4) reduction of errors concerning the avaiiaBle materais to mount casts in correct reiationship and onentation.

M. UacEntee. British Columbia. Canada Treatment Planning Using Computers: An Expert System to Guide tne Needy Expert systems in the he^th sciences were devised originally to reduce the stress on medical personnel in the midst of life-and-death decisions so that decisions could be based on more information than the medical professionals would normaiiy have at their disposal in resciving an emergency Over the last few years the Faculty of Dentistry at the University of British Coiumbia has deveioped a decision-support system to improve the process of screening, selecting, and tracking dental patients. The system records the oral heaith status of each patient during the course cf the initial dentai examination, and to date some 3.000 patient records are in the clinic's database Much nas been written about the decision-tree model in dentai treatment, however, this appears tc be the first successful software program with a wide and versatile ciinicai application.

W. Schneider, I. Wagner. Uppsala. Sweden

Dentistry at the Beginning ct the 21si Century—The impact of information Technology During the latter part of this centuiy the quaiity of diagnostic and treatment procedures in

Volume 12, Numbers, 1999

457

dentistry has improved significantly This was mainly possibie through continuing improvements with regard to dentai chair units, i nsl rumen Is. cameras, radiographie equipment, and Qental materials: in tne iast decade this improvement has been especiaiiy through an increasing avaiiabiiity of intormation technoiogy and teiematics(iTaT)-basedtooisthat support the cognitive work of the dentai team at chairside. Now treatment units comprising an open ITST platform have been introduced to the market, enabling integrated implementation of various digital instnjments and software tools in an adequate physiologic-and ecgnitive-ergonomie environmenl. A rapidly increasing number of significant innovations in the fields of ITST can be loieseen within the first decades of the new millennium. In the mew of dentistry the following will be of special interest: ¡t) continuing miniaturization of chip and sensor technology; ¡2) improved and innovative procedures for voiume data acquisition; (3) pioneering innovations in the field of augmented and virtual reality: ¡41 new tecnnologies and procedures for representation, storage, and retneval of knowledge, as weii as for fiexible iearning, le, leaming independent of time and location. It is the purpose of this paper to present and discuss the possibilities and limitations of ITST innovations to be expected in the next 2 decades with regard to their use in dentistry and oral heailhcare.

S. Seipel, Uppsala. Sweden Use ot Virtual Reality tor interactive 3-D Treatment Planning and Surgicai Na vigation in Impiantology Recentadvances in the deveiopment of va nous information technologies enabie ciinicians to apply new oi imprcvefl procedures for denfal diagnosis and freatment planning. With the advent of digitai 2- and 3-dimensionai imaging modalities together wifh computer based methods for 3-D visualization, new ways cf presenting and inteipreting radioiogic dafa and otner ciinicai data become reality Tlie presenfation gives a short overview about compufer-based methods originating from the virtual reality arena that will affect future clinical work in prosthodontics. In particuiar, the application of virtuai reaiity techniques is shown in the area of orai impiantclogy, demonstrating a number of pilot applications.

Examples discussed are implant treatment planning, surgical instnjment navigation, ¡aw-motien analysis, and interactive assessment ol virtuai prosthetic reconstructions.

I. V, Wagner. Uppsala, Sweden Nem Concepts ot Multimedia-Based informaimn Technology tor Ouaiity Management in Fiosthodontic Practice Indentistry ciinicai ivork requires advanced competence and ski il with regard to botti manuai and ccgnitive performance. Improved eiinicai outccmes can Be aeeomplished by supporting the ci inician in manual and/or cognitive activities Until now research and deveiopment were mostly concentrated on the manuai part, le. on improved instrumentation and chairside ergonomy. Obvious iy, even cognitive activities can be enhanced, especially by adequate information technoiogy and telematics (iTST)-based

The international lournal of Prosthodontics

International College of Prosthodontists

support. To identify needs for support ot cognitive activities in diagnosis and decision making with regard to seieotion and performance of appropriate ciinicai management, these activities have Io be analy¡ed wilh regard to the strengths and weaknesses of human cognitive performance. On the basis of such analyses it is then possible to support and enhance ciinicai cognitive perform anee, and thus to improve quality of care. It is the purpose of this paper Io present a chairside integrated IT&T-based support system specially adapted to different ciinicai work situations and built on physiologic- as well as cognitive-ergonomic principles.

Occlusion, Oral Physiology, and TMD A, Arlentl. S. Carossa, A. Grazlano, F. Navone, G. Pretl, C. Bucea, Turin. Italy Sleep Disordered Breathing in Complete Denture Wearers Obstructive sleep apnea (OSA), which is episodic complete or partial pharyngeal oOstruction during sleep, is a common disorder with potentially fife-threaten ing consequences.

We wondered whether in edentulous subjects sleeping without dentures may favor the occurrence of OSA by impairing mandibular posturai position and the relationships among tongue, cheeks, and lips. To explore this hypothesis we examined 12 edentulous subjects weanng complete dentures, 7 with OSA (that IS, with greater than 5 apnea-hypopneas per hour) and 5 without OSA. The 2 groups had similar ages and body mass indices. All patienis undenivent 2 polysomncgraphic studies on 2 consecutive nights, one with and one without dentures, in randcmi?ed order The anteroposterior pharyngeai wail distance with and without dentures was assessed by cephaiometry In OSA patients sleeping without dentures produced a significant increase in the apnea-hypopneas indes, with a greater number of both apnea and hypopnea episodes and a decrease in mean t\emogiobin saturation (SO^). Sleeping without dentures also produced disordered breathing in patienis without OSA, although the only significant finding was a higher number of apnea episodes, interestingly, removing dentures produced a decrease in the antefoposterior pharyngeai wail distan ce that was significant only in OSA patients. These findings Indicate that edentuious patients, particularly those with OSA, are at risk for sieep disordered breathing when sleeping without dentures.

P. Doglio, S. Carossa, F. Bassi, G. Preti, C. Bucea, Turin, Italy Orai Nitric Cxide in Nonsmokeis, Smokers. and Edentulous Subjects Nitric oxide (NO) is a gaseous free radical generated by the acidification of salivary nitrite, which through Ils antibacterial activity may contribute to the host defenses in the oral cavily We previously found thai orai NO production increases durtng dentai piague deposition and is inverse iy related to the number of bacteria contained in the

Theintemationai

piaque. The purpose of this study was to establish the normai range of oral NO production in view of future investigations on the role of NO in various dental and periodontai diseases. Wilh Ihis aim in mind we measured orai NO in subjects with natural dentition free from active denial or periodontai disease: 26 nonsmokers (14 men and 12 women, mean age 2B ± 2 years), 12 smokers (6 men and 6 women, age 25 ± 4 years), and 10 edentulous patients (8 men and 2 women, age 6 4 1 3 years). The subjects were examined in the moming, affer overnight fasting and accurate oral hygiene. Orai NO production was assessed by iniecling 30 mL of NO-free air inio the dosed and empty mouth, which was isolated from the upper and lower ain^ay by a speciai device, the injected air was withdrawn affer 30 seconds and analyzed for NO concentration with a chemiiuminescence anaiyzer. In nonsmpliers oral NO production was 53.0 ±2.8 ppb and was significantly higher than that found either in smokers (25.4 ± 4.5 ppb, P< 0.001) or in edeni ufo us patients (IB.4 ± 3.2 ppb, P< O.OOt ); no significant difference was found between smokers and edentuious patients. Our findings confirm the previous observation that smoking inhibits NO production. The comparison between nonsmokers and edentulous subiects indicates that natural healthy denlilion accounts for about ^. of fhe orai NO production.

M, Gross, Z. Onnisser, Tel Aviv, Israel The Eftect of Increasing Occiusal Vertical Dimension on the Lower Face Heigtjl The purpose ot this study was to evaluate the effect of increasing occlusai vertical dimension (OVD) on iower face height (LFH). This was done by measuring the efiect of a progressive increase in OVD on soft tissue landmarks on the iowerfaceatintercuspation(iC) and clinical rest position (CRP). Subjective evaiuation of changes in LFH resuiting from changes in OVD at IC and CRP was aiso assessed. The faces of 22 fuiiy dentate young adult subjects were photographed in a standardized manner in frontal view. Each subject was photographed with the leeth in IC and at CRP. Sequential photographs at IC and CRP were taken with 4 different acryiic complete maxillary occiusai overlays, increasing OVD in interincisai increments of 2, 4, 6, and 8 mm. Acryiic overlays had stable contact in IC and anterior diclusion. Objective measurements were made from the photographs using faciai reference markers, and 10 observers were asked Io make a subjective evaluation ot the resulting changes in tace height using the sequential photographs, which were prescaled randomly Resuits showed a corresponding change in LFH as a resuit of the incremental changes in OVD of 50% of the interincisai increase in OVD in IC and 40% for CRP. Anaiysis of variance for repeated measures showed a statistically significant effect of the intraoral increase on LPH (P< 0.001) and a significant effect of iC or CRP on LFH (P < 0.0001).

Subjective results showed that it was not possihie to distinguish changes in face height caused by intraoral changes in OVD in the range ol 2, 4, and 6 mm of interincisai separation, increase in face height was not in direct proportion to incrementai increase in OVDforbothIC and CRP SofI tissue compensation is likely responsibie for

i of ProsthodontiL-s

458

these findings. Increasing OVD in the range of 2 to 6 mm is not likeiy to cause distinguishable changes in LFiH. Conversely, increasing OVD with the express purpose of increasing iower face height may not manifest recognizable changes in LFiH in Ihe range of 2 to 6 mm.

S. IshigakI, E. f^orishige, K. Kajiwara, T, fliaruyama, Osaka, Japan The Effect oí Chewing Movements on Eti/IG Activities of tlie Cervical and Dorsal Muscles The aims of this study are to reveal: iUwhether there is a corresponding activity in cervical and dorsal muscles during chewing function; and (2) whether the size and hardness of the testing food affect those activities. Subjects were oomposed of 15 maies and 15 females.

Mandibuiar movemenfs during chewing and eiecfromyographic (EtiflG) activities of the anterior belly of the digastric muscle, the sternocieidomastoid muscle, and the postcervical and shoulder regions of the trapezius muscie weresimuitaneousiy recorded with the BioPAK System. The results of this study demonstrated corresponding cen/icai and dorsal muscie activities during chewing. Furthermore, these EMGactivities were affected by the siseas weil as the hardness of the fest food It was suggested that the stomatcgnathic function could affect the muscles of the neck and shoulders.

I, Klineberg, N. McGregor, H. Dunstan, H. Butt, T. Roberts, M. Zerbes, S. NIblett, Westmead, Australia Chronic Crotacial Pain Associafed ivil/i Dysregulated Cellular Proleolysis

tionfor which there is no known etioiogy Onset of chronic muscle pain has been associated with infectious events, trauma, and Increased life stress, each of which may induce an increased host energy demand. Painful muscle has reduced total protein and ribonucieic acid (HNA) levels without ioss of contractile proteins (Young, 1970), which suggests that short-term or nonfibriiiar protein, but not contractiie or fibrilla r protein, is being lost from painful músete. The aim of this study was to investigate changes in urinaiy ammo acids, which may indicate alterations in protein synthesis (leucine), nonfibrillarproteolysis(tyrosine), or fibrillar protein (3-methylhistidine). Twenty-nine chronic Type la (Research Diagnostic Criteria for Temporomandibuiar Disorders, Le Rescheetal, 1992) pain patients (MP group) and thirty-four age- and sexmatched control subjects were assessed for variation in urinary organic and amino acid excretion by gas chromatography mass specIrometry The MP patients had a reduction in the protein synthesis marker leucine (P> D 000001) and increase in the nonfibriliar proteolysis marker tyrosine (P < 0.05), but no alteration in the fibrillar proteolysis marker 3-methyihistidine.

Pain severity was associated with an increase in the tyrosineileucine ratio, excitatory aminc acids (glutamic and aspartic acids), and the total amino acids excreted, which suggested an overall depi etion of amino acids. These data indicate that dysregulated nontibrillar proteolysis and protein synthesis occur in chronic orofacial pain patients, which is consistent with the proposai

Voiume 12, Number 5, IE

Internationai College of Prosthodontists

that painful muscles show a reduction in total protein and the occurrence of ammo acidinvoked neuronal excilation [Coderre. 1993).

S. Kulmer. M. Hübe, W. Leja, M. Strainer, Innsbruck, Austria Stress-Induced Noncarious Lesions—Type ot Occlusion. Inclination, and Sequence of Guiding Elements and Wear Facets Noncanous lesions occur when the endurance limits of tooth materiats for cyctic toading conditions are exceeded over a iong penod of time The least muscle activity is aiways found in ocdusicns with a distinct front-canine guidance (mutuaiiy profected occlusion) Furlher, the angulations of the cuspai inclines—guiding elements and wear facets—and condylar paths have striking inftuences on the magnitude ot foices acting simultaneously in the joints and ttie dentiSon. A group of patients with noncarious lesions was diagnosed according to the guidelines for an updafed diagnosis regimen and initiai freatment ot the masticatoiy system (ARGE Profhetik und Gnathoiogie der Österreichischen Gesellschaff fur Zahn-, Mund-und Wefertieiikune, 19791. Guiding elements and weaJ facets were diagnosed in an individuaily programmed articuiator in conjunction with a lower pin model, and the inclination to the axis orbital plane was measured by means ot a 3dimensional digitizer. All teeth with nonoarious lesions were found in group functions, and in 89% rriediotnjsive contacts were also delected.

The guiding elements, oñen identically with wear facets, were significantly steeper than in the occlusions without noncarious tesions or ot normally develcped adolescents. The decrease ofthe inciinatrans ofthe guiding eiements (rom the front teeth to the second molars changed their sequence and characteristics completely.

It is concluded that group function and biiateiaiiy tjaianced occiusion promote the development of noncancus iesions V. Maeda, M. Soga, Y. Yonehata, Osaka, Japan Posterior Implant Support and the Shortened Dental Arcb Concept: A Biomechanical Model Analysis Käyser (19S1) infroduœd the shortened dental arch concept, in which bilateral occlusal support lothesecond premolars presences oral function and prevents temporomandibular joinf (TtvlJ) dysfunction. Käyser (1993) also reported that the use cf implants in the posterior region, combined with a cast metal lemovabie partial denture (MRPD), provides stable occlusai support and improves tunction and comfort even when bilateral ceci usai supporf tc the second premolars cannot be achieved. The obiective ot this study was to examine the efficacy of posterior impiant support in the mandible where posterior feeth were absent. A 2-dimensional finite eiement modei was conslrucled from a iateral cephaiometric radiograph Posterior occiusal 3up[>on was provided by a fixed impiant-suppcrted prosthesis oran MRPD with or without a supporting implant Force caicuiated Irom eiectromycgraphic data measured on the subject was appiied as vectors and stress distribution was anaiyzed in the TMJ region. Optimization

theory was appiied to simulate bone remodeling, ie, bone résorption and bone apposition in the TMJ region (Maeda. 1995) We assumed that when the occlusal support was stable the bone remodeling wasataminimumbecause the bone résorption equaled apposition. Although the fixed implant-supported prosthesis provided the most favorable and stable occlusat support we found Ihat a single posterior implant under the MRPD can help establish stable occlusal support in terms of bone remodeling.

C. iiianac. Bucharest, Romania The Impact ot trie Abraston Phenorrienä on the Dental Contact Aiea This study tnes to show the influence of tunctionat and pathologic dentat abrasion on fhe kinematic behavior of the proximat surfaces of the teeth in contact areas. The Investigation used a computational analysis modei achieved with finite elements. In a first stage the model was created as a standard sample of the kinematics ot fhis topographic coronary area of a natural tooth. In a second stage some clinical aspects closely related lo denial substance loss at different structural levels were simulafed. The temporal sequence ot these kinematic phenomena was determined in the respective topographic areas, creating a possible scenario forthe evolution otihese phenomena.

The functional relationship befween the rhythm of fhe occiusat modificalions and the geometry and funclicnality of the proximai zone engaged in fhe contact area was shown. This study shows the objective basis of the mesiat tendency already known about ihe teeth

mm (SD a 2 mm); ^had left-side shift and 'i had righf-side shift. The correlation between sagittat slide and laterat Oeviation is weak (r= 0.18).

In this study 6S% ol the subjects had a verticai component of tCP-RCP slide that was equal to or longer than the horizontal component, which IS easier to adjusi occlusaily; theother 32% had longer horizontal components of the slide, which are more difficuil to adjust.

T. Mar uyama, Osaka, Japan Healthy Face, Good Posture, and Occlusion A heatfhy face, which is an impoitani factor fot a beautitut face, is usually regarded as symmetric with a succession of coincidental i mes characterizing the dentai and facia i composition. When a divergence cf the face exists it goes without saying fhal the beauty ot the appearance IS reduced: divergence might aiso be evidence of functionat disturbance. The divergence of a tace generaiiy resuits in ihe deviation otthe mardibte, which is caused by abnormal occlusion. Good poslure is one cf the important factors lor an esthetic and healthy appearance However, thereare many tactcrs influencing tlie posture. Because ol an abnormal occlusion the mandibte is deviated and because of the deviation ot the mandible fhe head posture is deviafed Because of the deviation of the head posture the alignment of the cen/icat spine IS deviated. As a result the alignment cf (he whole spine isdevialed and the posture becomes poor. In this presentation the relationship between a deviated tace and posture and occlusicn, and theirtreatment, willbe discussed

L. r^arion, I. Kapac, Ljubljana, Si oven ia Electrognathographic Study ot Slide from Intercuspal to Retiuded Contact Position

R. Moazzez, D. Barttett, B. Smif h, f l . Wilson, London, tjnifed Kingdom Measurement of Oral pH in Patients with Dental Erosion

Sagittai contact movement trom intercuspat position (ICP) comprises anienor and postenor movement of the mandible. Posterior movement leads, via siide in centric position, to retnjdedcontact positron (RCP) otthe mandibte.

The aim of thisstudy was to measure tCP-RCP siideeiectrognathographicaily in the sagittai and horizontal planes In agroup of 38 young adults with a mean age 25.7 ± 4 years, Ihe computerized sirognathograph with Cosig softivare was used for recording and analysis of anterior mandibular poinf movement during ICP-RCP slide. The mean distance from ICP lo RCP was 1.4 mm^ the verticat dimension was 1 mm and the hon2ontat one was 0 9 mm. Vertical dimension of slide was longer Ihan the horizontal dimension in 47.7% of fhe oasesi mean ICPRCP disfance was 1.7 mm, vertical dimension was 1.4 mm, and horizontal dimension was 1 mm (SD 0.5 mm) Vemcal dimension of slide was shorter fhan fhe horizonfal dimension in 32% ofthe oases: mean ICP-RCPdistance was 1.0 mm, vertical dimension was 0.5 mm, and horizontal dimension was 0.9 mm (SD 0.3 mm).

Vertical and horizontal dimensions ot stide were equal in 8% of cases: mean ICP-RCP distance was 0.7 mm. verfical dimension was 0.5 mm, and honzontal dimension was 0.5 mm (SD 0.3 mm). ICP was identical with RCP in 13% ot cases. Everyone in the study had lateral deviation of iCP-RCP Slide. Mean lateral slide was 0.4

Dentai erosion is a common and increasing problem in adolescents. The cause of erosion is acids either found in the diet or from the stomach, ether factors are salivaiy ftow rate and bufferingcapacity, and also variations in the solubility of enamei in difterent sites and different patients Orai piH was measured simultaneously at the surfaces of 4teeth in 11 patients with ercsion and 10 control subjects without erosion (10 10 IE years ctd}. Smaii-diameter piastic tubing was piaced on study casts to match the path of fhe pH catheters and the appliance was fonned aroundthetubing.ThepHwas measured using minute antimony electrodes held within the vacuum-fonned appiiance and heid ftush with fhe looth surface. Measurements were made belore, during, and after drinking 330 mLof carbonated coia dnnk of pH 2.5 The severity and distribution of erosion were assessed using Ihe Smith andKnight(19B4) tooth-wear index. Reported dietary intake and the flow rate and buffering capacity of saliva werealso recorded The erosion patients had a higher intake of carbonated dnnks and reported drinking directly trom a can mere frequentty than the control subjects, who pref e n ^ a glass 1P< 0.05). Ttie pH at the labial surface of the maxiliaty central incisor fell below 4 0 for a gteater percentage of the time during and foilowing drinking in fhe controi subjects than in the patientswith erosion (P< 0.05). Tiiere was a trend tor the reverse situation on the tiuccal

Volume 12. Number 5,1999

459

The International loumsl of Prorttiodontics

International College oí Pnastliodontists

surtace of the maxillary first molar, where pH fell below 5,5 for a greater percenfage ot fhe time in fhe erosion patienfs. The results suggest fhaf dental erosion caused by acidic drini<s is probably relafed to bofh the frequency ot infake and fhe drinking habit.

H, Shiga. H. Hoimann, V, Kobayashi, Tokyo, Japan Change in Masticatory Moventent Due to Change in the Hacdness of Food The purpose of this sfudy was fo invesfigafe fhe eflecf of fhe hardness of gumi-jelly on masficafory movemenf during gumi-jelly chewing.

Twenfy healthy subjects (12 men, 8 women) in theii tivenfies were selected as subjects. Four types of gumi-jelly, which differed only in hardness, were used as fhe tesf focd. Gumi-jelly consisted of maltose, scrbifol, glucose, and gelatin. In this expenment fhe amount of gelafin was varied in four sessions fo maWe four ditferent hardnesses. While subjects were chewIng gumi-jelly en their habitual chewing side the mandibular moi/ement and masseter muscular activities were recorded simultaneously.

Four sessions of gumi-jelly ohewing with varied amounts of gelatin (5%, 6.5%, B%, and 9.5%] were performed. Analysis was perfomied on fhe ten cycles starting trom the íiíth cycle of chewing. First fhe masticatory path pattem was observed. Then fhe gape, the masticatory width, and fhe cumulative value of muscular acfivifies were each calculafed and compared befween each session. The masticafory pafh showed the same pattern v/ithin each subject regardless ofthe hardness of the food. The gape, fhe masticatory width, and fhe cumulative value cf mucular activifies were smallest when fhe amounf ot gelatin was 5%, They increased significantly as the amount of gelatin increased to 6 5%, 6%, and 9.5%. From fhese results it was concluded that in healfhy subjects fhe masticafory path pattern did nof Change during gumi-jelly cheimng; fo cope with fhe hanjness ot fhe food the amounf of lateral and vertical movements changed, whrch as a resulf changed ffie masticatory powor.

K. Yoshida, Kyoto, Japan Therapsuiic Effect of Oral Application for Sleep Apnes Syndrome Differs with Sleep Position Recenfly an oral appliance has been increasingly used for fhe freatment of sleep aprea syndrome, but the success rafe shows large Inlerindividualdifference caused by many tactors To elucidate fhe influence of sleep posifion on the therapeutic etfecf ofthe Esmarch device 58 patients wifh sleep apnea syndrome were investigated polysomnographically before and after insertion ofthe device. The sleep positions during each apriea were classified as supine, lateral, or prone. The mean apnea index (25,6 ± 18,7! decreased significantly (P< 0.0001} atfer insertion oí fhe device ( t l , 5 ± 12 6) The number oí apneas in the supine and prone positions was significantly reduced, from 18,0± 16.7 and 2.013,6 to 5,0 ± 11.2, ( P i 0,001 ) and 0,310,04 (P< 0,005!, respectively, buf fhat in fhe lateral posifion was slighfly increased, from 5.S ± 9,4 to 6,2 ± 8.9, The percent of apneas was 70,3% for supine, 21,9% tor lateral, and 7,8% for prone

beiorefherapyand43,5%, 53.9%, and 2.6%, respectiuety, after therapy. Thus, the effectiveness of oral appliance therapy cah differ greatly with sleep position The sleep position recorded polysomnographically may be important for fhe choice of oral appliance therapy and its prognosis. Sleep position training is an additional treatment for oral appliance fherapy.

Implants B, Andersson, P, Scharer, lA, Simion, CBergström, MÖlndat, Sweden Ceramic Implant Abutrrtents and Short-Span Fixed Partial Dentures: A Prospective 2- Year Multlcenter Study This is a 2-year report from an ongoing prospective 5-year multicenter sfudy. The aim ot the sfudy is fo evaluafe short-and long-term clinical tuncfionotCerAdapt ce ramie abutments [Nobel Biocare) supçiorfingshorf-span fixed partial denfures (FPD!. Inifially 105 Brânemark system implanfs were placed in a total of 32 patients at 3 difterenf clinics Affer inifial healing 103 implants remained. In alt, 53 ceramic and 50 fitanium abufmenfswereconnectedforfhesupport of 36 FPDs—19 on ceramic and 17on tifanium abufments. All patienfs remained atfer 2 years. There was a cumulative sun/ival rafe ot 97.1% for implanfs and a cumulafive success rate of 97.2% for FPDs (94% for ceramic and 100% tor titanium abutment-supported FPDs), One ot 53 ceramic but none ot the 50 titanium abutments failed, giving a cumulative success rate of 9B. 1 % and 100%, respecfively, for the abutments. Sott fissue around abutments and adjacent teeth appeared heallhy, filore crown margins were placed submucosally at titanium (31%) than af ceramic (14%! abufments, and the level of the periimplanf mucosa was relatively sfable in relation to fhe abufmenf/crown. No differences were seen between ceramic and titanium abutments regarding bleeding of the peti impianf mucosa. There was a minimal marginal bone loss recorded after 1 year, slightly more af fitanium [0,4 mm! ffian at ceramic {0.2 mm! abutments.

All pafients and clinicians were satisfied with fhe achieved esthetic resulf and no bridge was remade because ot compromised esthetics. So far fhe ceramic abufments have worked very well, but ceramic materials have exhibited sfaficfafigue. Thus, if is important to waif tor fhe 5year results before making any more definite statement about fhe long-term prognosis tor CerAdapf abufmenfs. However, fhe 2-year resulfs have been very encouraging for CerAdapt abutments supporting shori-span FPDs. D, Assii, I, Varsano, J. Nissan, A, Singer, Tel Aviv, Israel Accuracy of impiant impression Spiinted Techniques—Effect of Splinting Material Three implant Impression techniques using three diiterent splinting materials were assessed for accuracy in a laboratory mcdel fhat simulated clinical practice. Group A used autopolymerizing acrylic resin to splinf fransfer copings. In group B dual-cure acrylic resin was used, while group C involved plaster that was

I of Prosfhodontics

460

also the impression materiel used, A metal implant master cast with an implant master framework accurately fitted to it was made. The cast was fhe standard for all impressions. Fifteen impressions were made tor each group, Polyether impression material was used in groups A and B. The accuracy of the stona casts with fhe implant analogues was measured againsf fhe master framework using strain gauges, A multiple analysis ot variance (ANOVA) with repeated measures was performed fo test for significanf diííerences between the fhree groups. Addifional AVOVAs were carried ouf fo locafe fhe sources o( difference. The statistical analyses revealed thaf a significant difference existed between groups A and B (F, = 7.96; P < C.05), and between groups C and B (F, = 6,56; P< 0,05), buf not between groups A and C (F, = 0,25, P> 0.05), Impression techniques using self-curing acrylic resin or impression plaster as a splinfing maferiai were significantly more accurate fhan Uie light-oured acrylio resin. Plaster appears to be the material ot ohoice in fully edentulous patients, as if is muoh easier fo manipulate, less time consuming, and less expensive, P, Binon, Rosevllle. California Evaluation and Comparison of the Mechanicai Characteristics and interface Geometry of the Wide-Diameter Impiants with Special Focus on the Frialit Implant System The general factors contributing fo screw joint instability have been idenBfied (Binon, 1994), Dynamic loading tests have indicafsd thaf fhere IS a direct con'elation between screw looseningijoint failure, rotational misfit, tolerances, and screw-joint design [Binon, 1996a; Binon and McHugh, 1996; Binon, 1996b), The purpose ot this study was to evaluafe fhe mechanical characterlsfics and siabilify of several wide-diame1er implant/abutment geometries Implant Innovations [3i), Litecore, Asfra [AstraTech), ITI ¡Sfraumann), Spline (Sulier Calcifek), and Frialit-2 (Friatec) implanfs were evaluated as follows: torsion tesf, 30-dGgree stafic compression, rotational tolerance, hexagonal tolerance, residual torque, cyclic loading, and loosening moment. A standardized profocol was used for each of the tests, Teh implanfs of each geometry were tested. The cyclic loading Instrument used in four previous studies (consisting of fen piston heads driven by an elecfric motor that acf ivates a camshaft and delivers a 200-N load to each sample af a rate of 1,150 vertical cycles per minute as the samples rotate 360 degrees at 23 cycles,'mih CCW) was used. The resulfs of eacfi tesf will be reported and contrasted for each Of the geometries evaiuafed and com pared to values previously reported in the Iiferature for standard-diameter implants, Wide-diamefer Implants, in general, have significantly better meotianioal characteristics and improved stability during cyclic loading, G, Córtese, M. Aimetti, G. Schierano, MfiAozzatl, G, Pretl, Turin, Italy Histomorphometric Anaiysis of Human Psriimpisnt Son Tissue Periimplanf sott fissue has been exfensively studied in animals, v/hile few human sfudies

Volume 12, Number 5, 1B99

international Coilege oí Prosthodontists

have been reported This study reports a histomoiphometric analysis of periimplani sott tissue taken from human subjects by bloclt-section biopsy. Nine implants with no signs or symptoms of inflammation in nine healthy patients were selected. Five implants retained a mandibular overdenture and four supported fixed prostheses. A bloch-section biopsy thai included the transmucosalabutmentand a 2-mm-thicli circumferential section of pertimplant tissue, including epithelium, connective tissue, and periosteum, was taken under local anesthesia. Specimens were treated with resin, seotioned axially and sagittally to the long axis of the implant, and stained with a solution of hematonylin-eosin.

Ttie abutment was surrounded by a gingival sulcus lined with suicuiar epithelium. In the axial sections connective fibers were oriented parallel io the abutment, forming a conneotive ring.

In the sagittal sections the connective fibers were not arranged in an orderly fashion Numerous inflammatory cells were found in the penimplant stroma of all specimens.

• . Davis, tA, Packer, L o n d o n , U n i t e d Kirigdom Mandibular Overdemures Stabilized by AstraTecti implants with Elttier Bail Attachments or Magnets: 5-Year Resuits Tfie purpose of this presentation is to report on tfie use of implant-stabilEzed overdehtures in the mandible using the AstraTech implant system witti either ball attachments or magnets as the retentive mechanism. Thirteen edentulous patients were provided with mandibular overdentures that used ball attachments on two implants. Twelve edentulous patients were provided with mandibular overdentures, using magnet retention with two implants in ten patients and three implants in two patients. Once they were comfortable the participants were placed on annual recall. Any other visits were initiated by the patients. Detailed records were k ^ for ail visits. At annual recall the following parameters were monitored' plaque levels, mucosal health, marginal bone levels, and patient assessment ot the treatment. The patients were follcwed for 5 years There was no statistical difference between the two groups for mucosai health and postinsertion maintenance. The rragnet group had more abutment surfaces covered with piaque Statistical analysis of subjective palient assessment of treatment showed tfiat the magnet group was less comtortable and chewing was less effective. The results indicate that both ball attachments and magnets used on isolated AstraTech implants in the mandible are viable treatment options. Both attachment mechanisms provided patient satisfaction, although the ball attactimehts were better In this respect than the magnets.

D. Felton, L. C o o p e r , N. C h a f f e e , U. Palmqvisl, J. Moriarty, Chapel Hill. North Carolina Prospective Evaiuation ot immediately Loaded AstraTech MicrothreadedfTiOBiast implants with Mandibular Overdenture Prostheses The purpose of this investigation was to prospectively evaluate the clinical efficacy of 2 unsplinted AstraTech Microihreaded/TlOBIast

(AT-fiflT/TiOB) implants placed in a one-stage surgical approach and used lo retain a mandibular overdenture prosthesis. Mew complete dentures were fabncated for 60 totally edentulous patients. Following tomographic evaluation 2 AT-MTn"iOB implants were surgically placed in the mandibular oanine regions, healing caps were inserted, and tissues were sutured in a one-stage approach. The mandibular dentures were relieved trom the healing abutments and immediately inserted. At 7 to 10 days a tissue conditioner was placed over ihe healing abutments. At 3 months (baseline) balticap attachments were placed using a reline impression.

Radiographie, periodcntai (inllammation, pocket depth, attachment level, amount of attached gingiva), and prosthesis data (complications, loose abutments) were collected at baseline, and at 3-, 6-. and 12-nTOnth internals. The results showed that 5 implants failed prior to baseline, with noadditionalfailures noted (95.9% success rate). Periodontai and radiographie measures indicated a negligible increase in attachment levels (0.22 I 0.85 mm) and conical bone height (0.18 ± 0 54 mm) at 12 months. Prosthesis complications occurred with low frequency and included loss of retention of the ball/cap attachment, abutment loosening and fracture, and need for prosthesis relines and tooth replacements. Patient satisfaction surveys snowed an increased level of satisfaction with the overdenture prostheses. The AstraTech MT/TiO6 implants oan be safely inserted in a one-stage surgical approach and immediately loaded with an overi3enture prosthesis

L. Gassiho, G. 5c:hierano, K. Uareschi, F. Bassi, G. Preti, Turin, Italy Production d Cytokines involved m Bone Remodeling by Penimplant Soft Tissue and by me Mucasa Covering the Distai Ridge in Patients Wearing OvenJentures on Oral implants Tne stabiiity of dental titanium implants (Ti) is largely determined by their integration into the surn^unding bone. To better understand the mechanisms associated with this process we compared the production of osteotropic oytokines by gingival sott tissues (GST) in the edentulous ridge before and after implant placement. As deteimined by semiquantitative RTPCR, GST fn)m edentulous patients constitutiveiy expressed interteukin (IL]-1p, IL-6, and IL-B, and low amounts of IL-11. stem-cell factor, and transforming growth factor (TGF)-01, 2. and 3; transcripts for tumor necrosis factor (TNF)-u and granulocyte macrophage-cclony stimulatng factor (GM-CSF) were absent. When the same patents were treated with endosseous TIs and overdentures, penimplant GST, starting at the time of abutment connection and for at least 12 months after implantation, revealed markedly higher TGF-R1, 2. and 3 messenger ribonucleic acid (mfiNA) levels compared with those detected in the GST before implanfaiion.

In addition, expression of IL-6 and IL-8 decreased 8 months after TI piaoement, and that of IL-ip increased at 12 months. Simiiar timedependent pattems of cytokrne secretion were observed in cultured gingival fibroblasts derived from the same gingival biopsies. Interestingly, the increased TGF-fl mRNA ievels atter impiantaton were not confined fo the periimplant

Vdume 12, Number 5, 1999

461

zone but were also found af distances ncf accessible to diffusion of local factors. We suggest that the biomechanical stress created by the new implants may contribute to the reversal of the cytokine profile produced by GST in the edentulous zone in favor of one that supports bone deposition P. Gehrke, T. S c h n a b e l , fiíannhelm, Germany Preservation and Reconstruction ot the implant Interproximal Space. A Prosthetic Guideline for Rapiiia Regeneration Sott tissue management in implant-proslhetic rehabilitation is an important factor for the esthetic long-term success of the complete restoration. Ma|Or significance is attributed to the anatomic molding of periimplant soft tissue in the anterior region, which can be influenced by different factors; implant placement considering ihe quality of bone; mesiodistai and vestibulo-oral divergences from the optimal implant position; and axial divergence trom the optimal implant position. The importance of a global implantolcgic concept with the goal of recon stnjctin g the interdental space has been documented in the literature The interpronimal space for papilla reconstruction is influenced by contact, contour, and shape of the adlacent tooth and implant crown. The vertical distance between implant analogue and contact point should not eiceed 5 mm and tne horizontal distance should not be larger than 2 to 3 mm. Asimilar anatomic profile is attributed to each tooth group requiring an individual shaping of the periimplant soft tissue It should be possible to control the tissue reaction during the regeneration phase. Prefabricated implant abutments can meet the requirements for a natural emergence profile only to a limited extent. A wide range would be necessary to meet individual anatomic requirements. An esthetic, natural emergence profile can only be achieved with custom-made acrylic restorations. Shortand long-term temporary restorations can be fabricated either in the laboratory or chairside.

Individual periimplant sofi tissue shaping with a provisional Peek abutment (Frialit-2 ProTecl.

Friatec) during different prosthetic phases lollowed by the final restoration with an AI^Oj oeramic abutment (Frialit-2 CeraBase, Friateo) will be demonstrated and disoussed.

A. Hamade, J. C. López Noriega, f^exico City, Mexico Wide-Diameter Versus Standard-Diamsler implant Placement Pollowing Tooth Extraction The aim ofthis study was to determine the success rate and the amount of marginal bone loss around implants placed following tooth extractions in patients with advanced periodontai disease. A protocol was designed for patient selection and treatment. Customized radiographie and surgical stents were fabncated for every patient. Patients were premedicated with antibiotics and chlorhexidine-based mcuthrinse twice a day l weel< pnor to and 1 week atter the surgery Group i consisted of 20 standard hydronyapatite-coated 3.75-mm-diameter implants (Paragcn) and group II consisted of 20 wide hydroxyapaiite-coated 5- or 6-mm-diameter

The International Journal of Prosthodontic

International College of Prosthodontists

implants (Replace, Steri-Oss). All implants were placed by the same surgeon to replace anterior premoiars or moiar roots. All gaps between implants and socket walls were filled imth demineralized freeze-dried bone and covered with a resorbable membrane. Radiographie evaiuations were made immediately affer impiant plaeement and after 1, 3, and 6 months to assess bone ioss ievels. Analysis of varianee was performed to anaiyze differences befween groups. One impiant from group 1 was lost in the study. The standard-diameter group showed significantly more Bone iess (F< 0.05) in comparison to the wide-di a meter group. There was no statisticai difference in success rate between the groups. The resuits of this study reveai that immediate implant piacement foliowing tooth ertraction is an excellent chcice fo avoid residuai bone résorption for patients with compromised bone height in complete or partially edentuious jaws. This procedure certainly shortens treatment time and to some extent iowers treatment cost.

S. Hansson, Göteborg, Sweden Dsntal Implant Design for Enhanced Pixation Strength The success rate of dentai impiants is correiated with the amount of bone and tf^ quaiity of bone.

This indicates that overioading is a major cause cf dentai Implant loss. According to WolU's iaw bone modeling and remodeiing is the resuit of mechanioai stresses in the bone. To maximize the fixation strength in the bone dentai impiants shcuid be designed so that aii surrounding bone gets adequate mechanical stimulation and the stress peaks are kept at a minimum. Some design features, which in this way are suggested to promote the anchorage strength, are discussed. It is suggested that marginal bone résorption can be interpreted asa biomechanical phenomenon according to Wolff's law.

K. Holmgren. Stockholm. Sweden Cresco Ti Precision t^ethod—A New Method to Produce Implant-Supported Bridges in Cast Titanium Ali metals change form and size when being cast. Discrepancies rn accuracy cause constant tension between the superstmcture and the implants, jeopardizing their osseointegration. A method to produce superstnjctures wiBi passive lit on osseointegrated impiants has been developed. The technique eliminates dimensionai distortion and therefore potential preload caused by limitations in casting methods and metai properties. After crdinate surgical procedures, osseointegration, and healing ofthe sofi tissue, impression copings are fixed direcfly on fop of fhe implants and an impression is taken with an elastic matoriai. Anaiogues are mounted on the copings, whereupon a siiicon material is poured afcund the copings and part of the dummies.

The silicon material is removable, making it possible to inspect the eontaet between the dummy and the bridge tube. The working model is then poured in piaster, in the next step bumout piasticlubes are mounted on the anaiogues and the framework is waxed up and cast in pure titanium. The cast titanium framework is fitted, free of fensicn, on fhe working modei. In a special

precision fixa tor the wortting model and the framework are mounted with piaster on iron plates. By orienting the working modei and the framework perpendicuiar to a vertical axis in the fixator. it is pcssibie to give them exact and fixed posifions in relation to each other and to a caiculated horizontai plane through the supporting titanium Bridge tubes. The framework and the working model are then separated, and pretabrtcated titanium abutments are fitted on the anaiogues of fhe working modei. Both models are thereafter placed by the aforementioned metai plane in a computeriïed machine {Cresco Ti Precision Machine) that registers ahd calcuiates the exact position of each cut through the bridge lubes of the framework and fhe prefaBrieated abutments on the working modei. which are then cut individualiy This achieves parailel dispiacementin the horizontal plane for each individual cut. The resuiting optimum iength of the supporting bridge tubes is essentiai for esthetie and technical demands, it makes it possiBie to cover the metai with ceramic or acrylic down to the gingival ievei, avoiding visibie metal and improving the esthetics. The prefabricated titanium abutments on the working modei are cul exactiy in the same horizontal piane as the supporting Bridge tubes on the framework, making It possibie to iaser weid the tubes with very high accuracy. The advantage of this method is fhaf the precision-made titanium framework acquires a passive fit to the working modei and in turn to the implants. The method is buiit on an Ordinate dentai iaboratory technique with waxup and casting, which make it possible to have an individually formed superstructure. When high precision is necessary the Cresco Ti Precision Method, lAith its high industriai technoiogy, gives the opportunity to accurateiy fit the implant-supporied fixed partial denture.

S. Karlsson. J. Wennsträtn, J . Lindhe, Göteborg. Sweden Restoration of Function with the Use of Dentai implants in Periodontally Compromised Patients: A 5-Year Study The periodontaiiy ccmpromised patient is characterized by advanced loss of supporting soft and hard tissues. The tooth regions mostiy severely affected are the posterior segments As a consequence, following the loss of teeth affected by advanced periodontitis the aiveoiar Bone ridge will show marked reduction that may offer limitations with respect to implant therapy.

This study aimed to analyze the use of implanfs in partially edentulous pafienfs who have experienced loss of teeth because of advanced periodontai disease. A total cf 5Ë patients ref en^d for treatment of advanced periodontai disease was recruited, with a mean age of 5S years (range 34 to 7a years). A totai of 14g dentai implants ¡33 in the maxiiia and 66 in the mandibie) (AstraTech)was placed. After healing, standard abutments were connected, foiiowed by treatment with a fixed partiai denture (FPD) in the iaterai segments. At the foliow-up appointments the period on lai ahd pen impiant soft tissu es were examined with respect to ciinicai signs cf pathoiogy. Postoperative radiographie examinafiohs were performed at FPD insertion and af annuai foiiow-up examinations. When the data vieie analyzed 53 of the originai 56 patients remained

The internationai lournal of Prosthodontics

462

in the study. Radiographie signs of loss of osseointegraticn were hot found at any of the impiants during the observation period. Duringthe first year of foliow-up the mean ioss of bcne suppori af the 14B implants was 0.31 mm. At the subsequent annuai examinations the bone loss assessed in reiation to Baseline did not show mean values above that observed during the first year after ioading. During year one ofthe fclicwup period 37% of the impiants did not demonstrate any ioss of supporting bone. The corresponding value during the second year was 55% This study shows that treatment with impiant-retained FPDs ean be sueeessful even for peridontaiiy compnümised patients.

K, Koyano, Y. Matsushita, i^. Klhara. M, Tokuhisa, M, Hoshi, Fukuoka. Japan A iViodiUed impiant impression Technique and its Accuracy In a eonventional open-tray technique impression material is poured on the tray before the tray Is set into the mouth. Therefore, it is not easy to aiiow the guide pins to protrude from the tray opening because the guide pins are invisible. If the guide pins do not protrude from the fray opening because the guide pins are invisible, the impression cannot be removed because the guide pins cannot be loosened. If the opening is widened the positioning of the tray becomes easier. However, impression pressure would be decreased and the impression ofthe soft tissue around impiants may be incompiete Further, if the tray is repositioned several times there may be bubbles in the impression. To solve these probiems we deveioped a modified technique that has been used in our ciinic successfuliy. The purpose of this presentation is to introduce this technique and investigate its aeeuracy. In the modified technique additionai hoies are driiled on the buccai surface of the tray. The hoies are placed near the impiants and the impression matenai is injected through this hole after the tray IS placed in the properposition. The positioning of the tray is very easy because the impression material is poured only on the area arouhd the remaining teeth and the head ofthe guide pin is visibiethroughthe top opening After confirming proper positioning impression materiai is injected through tfie side opening. The accuracy of this technique was examined and compared with conventionai impression procedures by the experimental implant modei. Woiking casts were madefrom the impressionstaken from fhe same master modei with the conventional and modified techniques. Coordinate values ofthe reference points on the woiking casts wete measured by 3-dimensionai digitiier (Xyzax. Tckyo Seimitsu) and compared There was no statistically significant difference between the 2 techniques. It is coneiuded that the modified technique IS a reliable and precise impression procedure, even for inexperienced clinicians.

K. Michalakis. A. Pisslotis, Thsssnlonikl, Greece Cement Failure Loads ot Four Provisionai Luting Agents Used for the Cementation of impiant-Supported Fixed Partiai Dentures Overthelastfew years there has been remarkabie progress infhefield of impianf dentistry. At

i 12, Numbers, 1999

International College of Prosthodontists

the same time, many questions have arisen regarding the materials used and the techniques foliowed in clinical practice One of these ••hot" questions is related to the method of fixation of fixed partial dentures (FPD) to the underlying implants screw retained or cemented? Screw-retained prostheses have the big advantage of easy retnevability, but It is very difficult to obtain a passive fit of the FPDs on the implants. As a result, loosening or breakage of the fastening screws is common. Another disadvantage of this method is the occlusai access hole that creates an esthetic problem. On the other hand, cemented FPDs do not have the abovementioned (Ssadvantages, but the lack of retrievability associated with them is a major drawback. The ciinician therefore faces a big dilemma: retrievability or technicaüeasibility and esUietics? The purpose of this presentation is to compare the cement failure loads (CFL) of a 3-unit FPDiuted to 2 UCLA abutments (5-mm-high chimney) and of a 4-unit FPD cemented on 4 UOLA abutments 24 hours postcementation to find the •weakest" provisional cement, which consequently would be the best for this clinical procedure. For the 3-unit FPO 2 Brânemari( implants (3.75 mm) (Nobel Biocare) were embedded in self-curing transparent resin. The distance between the 2 implants was 15 mm, approximately the distance from the center of a fiist premolar to Ihe center of a first motar For the 4-unit FPD 4 Bránemark implants (3.75 mm) were used The distance between them was 7 mm. The ÜCLA abutments were plastic with a geld hexagonal collar and they were cast with a high-preoious alloy (Olympia, Jelenco). The FFOs were constructed from the same alloy.

The luting agents used for this study were (i) Temp Bond (Kerr), (2) Temp Sond NE (Kerr). (3) Improv (Steri-Oss). and (4) Nogenol (GC).

Cements were mixed according to the manufacturers' instnjctions and a quantity of 0.01 mL was used each time for the cementation of each FFDretainertotheUOLAabutments. Tiie prostheses were seated with finger pressure folIowedbyaioadof5kgfor10minutes Thespecimeris were stored in 100% humidity at 37°C for 24 hours before a uniaxial tensile force was applied to the FPD by a mechanical testing instrument The CFL was calculated in kilograms. For each luting agent 10 samples were prepared and the mean CFL was determined for each one. The results of this study will be discussed and the clinicai applications will be addressed.

P. Naert, D. van Sleenberghe, G. De Mars, M. Ouirynen, G. Maffei, Leuven. Belgium A Prospective Split-Moutii Comparative Study of Two Screw-Stiaped Self-Tapping Pure Titanium Implant Systems Clinical data indicate different mid- and longterm outcomes of endosseous impiants tor different configurations, in partioular the implant surtace. The present sludy oompares 2 implant systems wih different surface characterislcs in a split-mouth-randomized design. The AsfraTech (A) system (AstraTech) consisted of self-tapping, T i 5-bias ted, s crew-shaped implants made of commercially pure titanium, and Ihe Bránemark (B) system (Nobel Biocare) consisted of self-tapping Mark II impiants with machined surface irregularities. Throughout

Ihe 2-year observation period no significant difference could be lound concerning probing depths, presence of plaque, or change in marginal bone level. A statistically significant difference in location of the marginal bone level in relation to the shoulder of the implanl was found in favor of Ihe A system both at baseline and after 2 years Cumulative success rates of 100% (A) and 97.7% (B) were nof statistically different. From a prosthetic point of view more soldenng points were needed for system A compared to Bto reach clinically acceplabfe fit.

More years of observation are needed to compare the fate of the soft and hard tissues surrounding the 2 different implant surfaces.

G, Papauasiliou, P. Kamposiora, J. Strub, A. Tripodakis, Athens, Greece Computerized Stress Analysis ot a HooiAnalogue Impiant System As knowledge on osseointegration increases many researchers advocate immediate implant placement in bone sockets of freshly extracted teeth. Re-Implant (Re-Implant), a root-analogue implant system, was created to solve the problem of incongrue nee between extraction sockets and conventional screw- or cylinder-type implants. The purpose ol this study was to use 3dimensional finite element analysis to analyse stress distribution patterns in bone surrounding Re-Implant fixtures. The secondary purpose wastocomparestressdistnbutionforRe-lmplant fixtures made of titanium (Ti) or yitfrium partiallystabilized zirconium dioxide (YPSZ). Two models of a maxiiiary incisorwith Re-Implant fixtures in fhe two different materials were made A porcelain-fused-to-metai crown for the Ti implant and a ceramic crown for the YPSZ implant were modeled. The implant-crown complex was embedded in cortical and cancel Io us bone.

Loads of 100 N were applied obliquely on the paiatal surtace at the middle third of the crown.

Key regions were selected within ihe bone-to-implani junction for compansons among models.

Stress levels were calculated according to the Von Mises entena. High stresses were observed in the area where the implant entered the bone.

Stresses were higher at the facial and lingual surfaces than at the proximal ones. In cortical bone and at the junction of corticai and cancellous bone, stress distnbution presented a pattern of altemating high (40 to 50 N) and low (13 to 20 N) stress areas High stresses were found at the apical third of the implant-to-bone junction as well. Results indicate that Re-Implant root-analogue implants presented a favorable stress distribution at the bone-to-implant junction. This distribution depends on both the macro surtace (honeycomb) and the root form of the impiant The YPSZ implants had very similar stress distnbution to the Ti ones and can be viable alternatives, especially in anterior regions.

A. Pissiotis, A. Sofou, Thessaloniki, Greece Comparai) ve Study of the Retenti ve Capacity of Different Types of Overdenlure Ball Attachments Used for Implant-Retained Overdentures Patients with mandibuiar dentures with poor retention and stability can be treated successfully today with osseointegrated implants. The most common and simple treatment plan is the

Volunie12.Numbers, 1999

463

construction of an overdenture wilh Ihe placemen! of 2 implants in the mandibular canine area and Ihe use of either a bar-clip ora bali attachment with an 0 ring as the overdenture retention mechanism. The combination of the ball attachment and the 0 ring is available from the implant manufacturers. It consists ot an abutment in various lengths, depending on the mucosal thickness, that carnes the ball attachment and an O ring with a housing—in either plastic or metal—that is embedded in the acrylic of the overdenture. Several ball attachments with O ring assemblies are commercially avaiiabie to fit the Nobel Biocare implants. The purpose of this study was to measure and compare the retentive ability of each type of ball attachment. For this purpose 2 Nobel Biocare implants were placed parallel to each other m an acrylic resin block. The ball attachments selected were the Mobel Biocare overdenture attachment, the 3i overdenture attachment, the Steri-Oss overdenture attachment, the Lifecore overdenture attachment, and the Hem overdenture attachment. Acrylic ove days were constructed, resembling an overdenture carrying the O rings with their housings. Each overlay had a hook positioned in the middle to allow it to t)e pulled away in a vertical direction by a universal tensile testing apparatus. Each overlay was placed on the implants and was pulled by the tensile testing apparatus The force required for every type of attachment was calculated The differences between the types of attachments will be piesented.

G. Ravasini, Parma, Italy Medular Transilional Impiants I was the first to try the Modular Transitional Implants (MTI, Dentatus) in 1993. and I have many beautifui cases from I hat time with complete follow-up documentation—tsoth fcr traditional implant provisional abutments and for fixed partial denture repairs With 5 years of experience I was able to develop a protocol to show the best way to use this new. attractive, and unique technique, which also allows a fixed provisional partial denture in totally edentulous patients during the integration cf traditional implants.

K. Saratani, H. Oka, f^. Tatsuta, S. Shi, Y. f^atsutani, M. Iwata, T. Kawazoe, Osakashi, Osaka, Japan impiani MobilHy Evaluation by Bender-Type Tooth Mobiiity Tester Loosening of an implant is a reccgnizable sign of dysfunction or disease of the periimplant tissues. The mobility of implants has been obtained clinically by applying force with tweezers However, ilis difficult to objectively detect slight changes in implant mobility with this method.

Eariy detection ol impiant mobility may allow suitable treatment to be carried out while the changes in the pertimplant lissues are still reversible We previously developed an automatic diagnostic system for tooth mobility, which measures the biomechanical properties of the peiiodontium by applying a random vibration to the looth. Since the Impedance head of this system is too iarge to measure mobiiity in an implant abutment and a molar, we have developed a new tooth-mobility tester. In this tester a

Journal of Prosthodontics

International College of Prosthodontists

sinusoidal vibration is appiied to the tooth crown and acceleration response is delected. The measured value is proposed as an index of the tooth mobility, the Mobility index (full) score. The bender-type probe cf Ihe tester is small, light, and suitable for oral examination. We applied this tester for evaluating implant mobility in clinical cases, and found that Ml scores ot the implants were smai 1er fhan those ot teeth.

The authors would like to acknowtedge Ihe Scientific Research Fund ot the Japanese Ministry of Education, Sports, Science and Culture |No. 0845519S, 10045078lfor Its support.

A. Smidt, Tel Avi«, Israel Implant Site Development—Orthodontic, Surgical and Prosthetic Augrnenlative Procedures Combined mith an Innovative CAD/CAM System m Single Tooth Restoration The success of impianl-assisted restorations is not oniy evaiuated by the ability to supply function but also by the ability to recapture naturat esthetics. The combined procedures of imptant sife preparation, implant piacement, sott tissue treatment, and prosthetic-guided heaiing prior to the restorative phase aii contribute to !he finat expected resuit Exerling extrusive forces on the hopeiess footh prior to its extraction augments the bone without any surgicai procedure.

The doomed tooth sen/es efficiently to improve the bone architecture in aii dimehsions, creating an extraction site ready for impiant piacement whiie simultaneousiy enhancing the soft tissue topography. Following are impiant piacement, bone integration, and second-stage surgery, which inciude important steps toward the creation of Ihe soft tissue frame surrounding the tuture prosthesis. Then begins the finai restoring phase, adapting a crown to the formed recipient site. This presentation wiii show how to prepare and "augment" a prefabricated ceramic abutment (CerAdapt, Nobei Biocare) fo mimic a root toirn and act as proper support forthe fissue and the final restoration after the careful creation of the implant site and the soft tissue frame. An innovative compufer-aided design/manufacturing (CAD/CAM) crown system will be presented as a complementaiy choice tor the augmented ceramic abutment. The objective of this presentation IS to discuss [he stages in preparing a potenfiai site for an impiant and the implant piacement, the importance of soft tissue fopography in the creation olthe ittusion. and fhe roie otthe restoring ciinician in Ihe finai stage toward achieyingwhai is considered by both the patient and the ciinician to be a lifelike appearance.

G. Szabo, L Kocsis, P. Szanfo, F. Thamm, R. Wohlfan, A. tWike, Pecs. Hungary Abutment Screw After Simulated Function The aim of this investigation was tc evaluate changes in torque by using anaerobe-adhesive seaiant on the interface of impiant abutment screw joints during apptication of static and dynamic leads, implants and straight abufments for cement-retained restorations beionging to 2 Hungarian impiant systems (Dentimplant and Uni plant) were seiected where a 4.4-mm-iong active screw surface was measured in a profile projector at 50y.. One type ot abutmenl was

constructed with a circular inner deagn, while an anti rotation a i eiement was buiit info the second type of abutment Tc increase Ihe lorque slabiiity between titanium surfaces Ceka Bond (Ceka) was used as a representative of anaerobe-adhesive seatant The test assemblies ot implant, abutment, and cemented crown were fixed in acryiic resin specimen holders. To ensure a constanttighteningmovementcf22.6Ncminan accurate and reproducible way a torque gauge was designed and connected to an eiectronio monitoring system. Dynamic load was appiied by a vibration excite' woriiing at a frequency of 1.42 i-tz and an ampiitude of 1.00 mm. The forque necessary to ioosen each screw was fhen recorded. At basetine a decreased torque of 18.3 and 1S.1 Nom was measured However, fhe locsening torque of 50 and 40 S Nem was reached using adhesive seatant atter the cyclic load. From fhese preliminary results it can be concluded fhaf the adhesive seatant on the interface of implant and abutment screw may increase to a great degree the torque stability of an abufment for ce ment-retained restorations.

Supported by OTKA T026063 A. Tripodakis, Afhens, Greece Immediate Implant Placement Combined with Controlled immediate Loading in Single Tooth Replacement immediafe impiant piacement following the extraction ot hopeless leefh has been used successtuliy foiiowing a certain ciinicai protocoi.

The am of ihe present approach is to combine the immediate impiant with fhe insertion of the provisional restoration to maintain the soft tissue architecture. Atraumatic extraction of the hopetess tooth is followed by curretting the socket without raising a ftap. The impiant site is prepared In a paiatai direction so that the imptant is engaged by sound and heaithy bone. A long heaiing abufment is used instead of a cover screw so that Ihe iabial tissues are pn:iperiy supported An immediate resin-bonded metalacryiic fixed partiai denture retained on the paiatai surfaces of the adjacent teeth is used as a provisional restoratimi. The cenjical part of the pontic is adapted on the coronai part ot the heaiing abutment. As a resuit Ihe impiant is passivety ioaded and spiinted to the adjacent teeth and fhe soft tissue architecture is furfher supporfed.

Stage 2 surgery is therefore totally eliminated.

So far 6 maxillary restorations (2 cenfrai incisors, 2 lateral incisors, and 2 first premoiars) have been successfuiiy accomplished foiiowing the above protocoi. The short-term results have shown thaf ali impiants integrated and sofi tissue architecture was tully maintained.

L. Van Zeghbroeck, Gent, Bet g I um Tissue-Integrated Implants as Strategic Additional Anchors to Support a Removable Partial Denture In complicated mutiiations or in mutilations with iocai bone defects surgicai techniques such as bone grans, in combination with tissue-integrated orai impiants. allow us to reconstnictthe dentition with a fixed partial denture, l-lowever, there are occasions, especially in restoring iarge edentuious areas in the parti aii y edentulous

The International journal of Prosthodontics

464

maxiiia, when afixed appliance does not satisfy the patient's requirements for esthetics, good phonetics, proper orat hygiene, and oral comfort al an affordable price. Especially in oases cf trauma or after local lum op resection, Ihe mutitated dentition shows some intact remaining teeth and heaithy periodontai support, which are unable to bear Ihe forces ot mastication and the impact ol a metai-frame removabie parfiai denfure in a ngid way. The use of oral implants— caretullychosen as strategic additionai anchors in the large edentulous area—allow Ihe creation otan individually designed su perstaictu re on impiants. This aiiows the ngid design of the metat-trame removable partiai denture to toliow the chosen rests, guide ptanes, and piacement of retainers as far apart as possibie for optimal support, stabilization, and retention on both superstructure and natural abutments. All occlusal forces are equally disfributed and forque or risk of overload is avoided on both abutment teelh and implants. The oral management ot cases with the combination of toothand impiant-supported removabie partiai dentures IS presented and discussed. A combined classic hybrid removable partiai denture that is fabricated to fit an individually miiied rigid bar connecting tissue-integrated implants and residual dentition, and is designed for maximal stability and to meet phonetic and esthetic demands IS a successful treatment tor motivaled patients.

S. W. Yi, Seoul, Korea A Three-Year Prospective Study of implantSupported Prostheses for Rehabilitation of Periodontally Compromised Dentitions The aim of this study was to evaluate the result of the rehabiiitation of periodontaiiy compromised denttons by using AstraTech implantsupported prostheses |ISP). Endosseous implants (n = 110) were piaced in lorty patients with penodonlaiiy compromised dentition. Rveorsix impiants were piaced in five patients after the extraction of all teeth in one jaw because ot a poor prognosis and two to tour impiants weie placed in thirty-five partiatty edentulous patients. Atter osseoihtegration the patients were provided with fixed ISPs. No impiants were iost. The mean totat marginat bone ioss was 0.34 mm in fhe edentuious patients and 0.30 mm in partialiy edentuious patients afterfhe ISPs had Iwen in sen/ice tor 3 years. The tew complications observed were porcelain fractures in two superstructures and fracture of one bridge screw.

Patients' opinions on oral functions—mastication, phonetics, hygiene, ccmfort, and esthetics—were evaluated by means ot a questionnaire both before implant placement and at the last follow-up. A great majority of the patients were extremely satisfied with the oral function after treatment and experienced the ISPs as "naturai teeth." There was no significant difference between the patients and the controls with natural teeth for mastication, phonetics, comfort, and esthetics. The patients reported a small but significantly greater diffiouity with oral hygiene procedures than the controls. Ali patients answered that they would undergo the treatment again and recommend it to others, it was concluded that the rehabiiitation cf periodontaliy compromised patients by using ISPs on

Volume 12. Number 5, 1999

Internafional College of Pros Ihnriontists

AstraTech implants resulted in subjectively improved and satisfactory oral function. Based on this 3-year study the system ofiered a reliable and predictable restoration ot fhe periodonfally compromised dentiton with tew complications, N-Zitzmann, C, Uarinelto, Basel. Swiberland Tieatment Concept lor the Edentulous Maxilla uith Implant-Supported Restorations: Fixed Versus RemovaDie Prostheses Restoring fhe edentulous maxilla with an implant-supported prosfhesis is a diagnosfically complex and clinically challenging procedure.

The crucial factors thaf are involved in deciding whether a fixed implant prosfhesis or a removable overäentu re should be ptanned to fulfill fhe pafients preference for opfimal esthetics, phonetics, comfort, and function are presenfed.

Biologic and technical, surgical, and prosfheSc parameters are discussed. An efficient diagnostic planning procedure fhat includes clinical and radiologie paramefers is the basis for a prediclable restoration ot ffie edentulous maxilla.

Tfie relevant facfors, such as case evaluation, dinical step-by-step procedures, advantages and disadvantages, and a time-benefit analysis, aie presented, Furfhermore, materials and methods for an implanf-supporled removable oveidenture leading to optimal tuncfion and an estiietic treatment soluton are demonstrated wtth clinical cases. Minimai résorption ot the aheolar bone and an optimal maxillomandibular relationship are prerequisites fcr an implanfsuppofted prosfhesis. The removable overdenfure offers a greater latitude in restonng patients who presenf wttfi any sott and/or hard fissue deficiencies, an inadequafe intennaxillary relationship, or a reduced number of implants.

Maxi I lofacial Prosthodontics H, M, El Fattati, Cairo, Egypt Surgical and Implant-Supported Prostheses m Rehabilitation of Patients ivdfi Oral Cancer Exfensive |aw resecfion for malignant oral lesions leads to considerable funcfional compromise. Prosthetic restorations witfi adequate support oan generally lead to satisfactory rehabilitation from a masticatory, phonetic, and esthetic perspective. Cohuentional prosthodonfic care is frequently nof possible because of fhe problemafic postoperative anatomy, especially in edenfulous cases. The present sfudy describes the use of endosseous implanfs and implant-supported prostheses in 13 tumor pafienfs. On the basis of positive resulfs with impianf-supported prosfheses the combination of surgery and implanfology has become an accepted rehabilitation option tor tumor pafients.

S. Esposito, Cleveland, Ohio Use ola Palatal Lift/Augmentation Prosthesis to improve Dysarthria in Amyotrophic Lateral Sclerosis Amyotrophic lateral sclerosis (ALS) is a progressive, adulf-ohsef neurodegenerativa disorder manifesting as a loss of motor capabilities and untimely deaf h. The dysarthria seen in pafienfs wifh ALS who have tiulbar symptoms causes severe problems with communication. The struggle fo be understood comes

Volume 12, Number 5, 1999

465

af a time when progressive cumulafive disabilities make communication with iamily, friends, and healfhcare workers vital. The use oí palafal litf/augmentafion prosfheses for dysarthria in ALS is nof a frequenfiy requested procedure by neurologists. This aufhor has been involved with fhe neuromuscularfeam at The Cleveland Clinic Foundafion, which is working in conjunction with speech pafhologists to manage fhe speech problems associated wifh ALS A relrospective sfudy of 25 patienfs treated wilh a prosfhesis was performed using chart reviews and phone/oííice ihterviews fo evaluafe fhe eííicacy of a palatal liñ and/or augmenfation prosthesis to improve speech in ALS patients. In addifion, a pilot prospecfive sfudy has been started. Results of these sfudies will be presented.

A. Shifman, Poetach-Tikua, Israel Prosthodontic Aspects Involved in the Planning of a Maxillary Resection This presentation discusses the reasons preoperative ccmmunicafion befween the maxiltofacial surgeon and fhe prosthodontist is of utmost importance in improving fhe posfsurgical qualify of life of ftie pafienf who is a candidafe for a maxillary resecfion Adjuvanf radiation therapy may atso be considered depending on fhe fype of fhe malignancy and the estenf of tumor Invasion, Consequenfly, sucha patient will preoperatively benefifirom: primary crisis infeivention; esfablishmenf of an intensive oral and dental treafmenl/mainfenance profocol; provision of a surgical obturator; and surgical modificafions designed to enhance prosthefic prognosis.

The International lournal of ProithodontiC!

Book Reviews Esthetics and Prosthetics: An Interdisciplinary Consideration of the State of the Art Edited by Jens Fischer Published by Quintessence Pui^iishing Co. inc, Chicago, 1999: 220 pages This textbooii offers a brief review of esthetic concepts in an attempt to blend information fiom various dentai disciplines as they reiate to esthetic concepts in dental treatment. The organization of the book provides the reader an easy-to-understand format vi-ith generous photographs and figures to enhance the written ihforniiition. The text is comprised of 7 chapters written by different authors; at times the transition between chapters does not flow easiiy, but each chapter is reievant to the primary emphasis of esthetics and prosthetits. This overaif focus helps to relate several topics to one another and aiiows a booii that is not limited to one specific type of restorative treatment for achieving esthetic resuits.

Many authors have presented similar information, but these authors offer a conc:ise review of the fundamentals in the initial chapter. Basic parameters for evaiuation of a patient's current esthetic status with reference standards are described. For example, when facial symmetry in reiation to the posterior tooth region, specifically the buccal corridor, is discussed, a simple illustration is included as well as a clinicaf photograph for reference, issues related to treatment planning are reviewed and include various prosthcxiontic treatment options including fixed and removabie prosthodontics and combination solutions. The proposed treatment concept is weii organized into a systematic protocol.

The information presented from a dental matenais perspective, a ceramic-fused-to-metal technique, outlines a methodical approach to compiex fixed prosthodontics. The high-quality photographs provide a laboratory sequence for obtaining precision laboratory results. The information includes specific sprue designs and a cutback design that gives tbe laboratory technician a predictable mean5 for fabricating a framework that resists deformation and provides space for porcelain veneering. The laboratory techniques include the suggested routine use of gold layers veneered onto the framework for optimizing esthetic results. The shade selection guidelines described are largeiy limited 1:0 a direct custom shade approach that necessitates direct interaction with a laboratory technician. The porcelain techniques and laboratory technician's perspective can be applied to various types of porcelain to enhance the esthetic appearance of the completed restorations.

The materials science chapter provides a succinct review of the properties of porcelain materiais used in metaUceramic and all-porcelain systems. The material is self-limited to tbe demonstration of specific materiais but still includes discussion reievant to the baiic components of porcelain and the changes that occur during the fabrication process. As with each chapter, references for additional reading are included but many are limited to German-language journals.

Tlie chapter thar discusses tooth conservation offers a perspective seldom included when discussing complex prosthodontics: operative dentistry. Although operative dentistry is intrinsic to prosthûdontic treatment, the shared goal between the disciplines is reinforced here. This chapter offers a nice review of current treatment protocoi in acid-etch procedures, presenting good references related to durability and results from clinical studies found in current literature. The discussion focuses on the decision process when treatment planning to emphasize the literal costs of

The International lournal of Prosthodontics

470

dental anatomy in achieving esthetics in fixed prosthodontics; ". . . superior esthetics (ceramic) of the prosthesis comes at the cost of dental hard tissue."

Resin-bonded restorative treatment and single-tooth implant treatment are addressed as alternative treatment possibilities for ioss of a single tooth, although the use of a resin-bonded restoration is discussed more thoroughiy. Clinical illustration of tiie preparation technique provides the current state of the art requirements for use of resin-bonded restorations.

The discussion of esthetics as it relates to implant prosthodantics is well organised and addresses specific considerations ihat can be applied to assessment in any type of prosthodontic patient care. Although the figures demonstrate appiications for use vi'ith iTI implants (Straumann), the topics can be appiied to most types of implants currently available on the market. The checklist of information discussed includes status of the alveolar ridge, status of the mucosa, crown margin, crown form, interdental spaces, occlusai surfaces and incisai edges, iip support, smile line, and long-term esthetic results. Once again the material is well orga.ni zed and succinct.

The final chapter addresses esthetics from an orthodontic per.spective. From a pnisthodontics viewpoint this chapter pmvides basic information that should be considered to balance one's approach to treatment. Not all successful results can be achieved through a iaboratory technician's skill alone. The patient pretreatment analysis may indicate orthodontic intervention to enhance resulti that may otherwise be compromised. Often, clinicians may focus on results based solely on their individual abilities ratlier than an interdisciplinary approach. This chapter also includes tables thai can be a valuable reference when considering ortliodonLic intervention, such as a list of indications and contraindications for space closure after the loss of anterior teeth or the review of treatment concepts for missing maxiiiary teeth.

This textbook is not meant to be a how-to guidebook for all esthetic challenges. Rather, it provides a review of principles from several disciplines to help one manage patient information in the development of a treatment plan with esthetic objectives. The title includes the term interdisciplinary, which the textbook does address, but this does not mean that all disciplines, such as specific periodontai procedures or major oral and maxiilofacial surgical intervention, are included.

General practitioners and prosthodontists wiii find this book to be a valuable review of multiple topics related to esthetics and prosthetics in addition to discipline-specific books that may include limited chapters related to esthetics in dentistry. Other specialists can use this book as a good review for communicating with referring practitioners; this may help referring clinicians understand the challenges a practitioner must face to achieve a patient-specific esthetic result.

—Reviewed by Lily T. Garcia. DDS, MS, Department of Restorative Dentistry. University of Coiorado Schooi oS Dentistry. Bouider, Coiorado.

Volume 12, Numbers, 1999

Advanced Removable Partial Dentures By james S. Brudvik Published by Quintessence Publishing Co, Inc, Chicago, 1999; 164 pages Treatment with removable partial dentures (RPD) has always been ¿ source of frustration for practitioners and patients alike. While this form oí treatment has been practiced for more than a century, there has been little evidence-based dentistry to support the principles and practices oí RPD treatmeni. The author states that this book is not an RPD test in tlie classic sense because it presupposes a basic understanding of RPD treatment; rather it is a monograph for tbe more advanced graduate student or study club participant to use in exploring RPD at the highest level of therapy.

This monograph reflects the knowledge base of the author, a clinician, researcher, and dental laboratory director who has spent 35 years seeking answers to the complexities DÍ RPD treatment.

This monograph has no bibliography. This is problematic for those clinicians wbo wish to search the relevant literature to substantiate the author's opinions, although the author slates this fact in the preface. All of the illustrations consist of black-and-white line drawings highlighted with red to emphasiîe salient points.

The monograph consists of 11 chapters covering the standard topics in RPD treatment—treatment planning, RPD design.

impressions, etc—plus an intniduction and an index; it h written in a strtiightforward conversational style. To the book's credit are the last 3 chapters, which cover about a third of the text. The "Special Prostheses" chapter introduces splinting with an RPD, hinged major connectors (specifically the Swing Lock attachment), and rotational RPDs. Common clinical procedures and the various current attachment systems in precision-attachment RPDs are covered in the "Precision Aftachnients" chapter. Newer methods oí support and retention oí RPDs by implants are covered m the chapter entitled "implants and Removable Portial Dentures."

While the information found in many of the chapters in this monograph is similar to much oí that covered in standard RPD textbooks, the chapters noted above make for additional interesting study for clinicians who wish to improve the quality of their RPD patient treatment.

—Reviewed by Roben P. Renner. DDS, Professor Emeritus, University at Stony Bnxik, Sdiool of Dentai Medicine, New York.

First Biennial Congress of tbe Asian Academy of Prosthodontics

lion has held 2 successful scientific meetings since it was founded.

Last year the name of the organization was changed from the ICPAC to the AAP. The AAP was started as a new prosthodontic organization that includes more Asian countries and individual members, with the goal of exchanging scientific knowledge and clinical experience, and encouraging bonds between members in different regions of Asia.

The next congress of the AAP will be held in |uly of 2001 in Singapore.

The first Biennial Congress of the Asian Academy of Prosthodontics {AAPl was held in conjunction with the 40th Anniversary Scientific Meeting of the Korean Academy of Prosthodontics from April 30 to May 2, 1999 at the Intercontinental Hotel, Seoul, Korea. More than 1,500 participants from 11 Asian countries attended the lectures, symposia, and oral presentations.

The group, originally known as ICPAC, was first organized m 1994, when 10 Asian countries Joined the group. The organiza-

Volume 12, Number 5, 1999

471

i of Prosthodontics