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May 2018 • Vol 7 Issue 2 • Payslips Are Important! A Practical Guide To Getting Them Right • Making Friends With Your Sintering Oven Heating Elements • A Comparison of the Change in Mandibular Condyle/Fossa Relationship with the Use of Anatomic Teeth and Semi-anatomic teeth in Complete Denture Prosthesis • Do Flexible Acrylic Resin Lingual Flanges Improve Retention Of Mandibular Complete Dentures?

SADTJ

ISSN 2077-2793

The Southern African Dental Technology Journal

2018 DENTASA SUMMIT & AGM 8.9

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In This Issue SADTJ Vol 7 Issue 2 May 2018

Editor

Axel Grabowski

Managing Editor Mariaan Roets

PUBLISHED BY

The Dental Technicians Association of South Africa

LAYOUT AND DESIGN Nicola van Rensburg

ADVERTISING ENQUIRIES

A Comparison of the Change in Mandibular Condyle/Fossa Relationship with the Use of Anatomic Teeth and Semi-anatomic teeth in Complete Denture Prosthesis

9 Do Flexible Acrylic Resin Lingual Flanges Improve Retention Of Mandibular Complete Dentures?

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m.roets@dentiworks.com

ADDRESS CHANGES

Elize Morris: dentasa@absamail.co.za

ACCOUNTS Elize Morris: dentasa@absamail.co.za

Payslips Are Important! A Practical Guide To Getting Them Right

31

Tell: 012 460 1155 Fax: 086 233 7122

DENTASA

PO Box 95340, Waterkloof, 0145 Tel: 012 460 1155 Fax: 086 233 7122 dentasa@absamail.co.za www.dentasa.org.za

Making Friends With Your Sintering Oven Heating Elements

Quality Control in the Laboratory

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STATEMENT OF INTENT The Southern African Dental Technology Journal is published quarterly. The main objective of the Journal is to provide the professional with the opportunity to earn CDP credits through completing the questionnaires, or writing articles. All papers in English, on any aspect of dental laboratory science or related disciplines, will be considered on merit and subject to the review of the editorial board and the CPD accreditation committee.

EDITORIAL, ADVERTISING AND COPYRIGHT POLICY Copyright of individual articles appearing in this publication reside with the individual authors. No article appearing in this publication may be reproduced in any manner, or in any format without the express written permission of its author and a release from this publication. All rights are reserved. Opinions and statements, of whatever nature, are published under the authority of the submitting author and should not be taken as the ofďŹ cial policy of the Dental Technology Association of South Africa.

SADTJ Vol 7 Issue 2

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Editor’s Page Time has come for north and south gauteng to be hosts for the DENTASA Summit and AGM. This, as mentioned before is going to be a weekend with a “ bushveld” feel to it. The booking is open, and we hope that we will be in a position to fill the entire venue for the weekend of the 20th and 21st july 2018. The organizing committee is once again in the process of attempting to get as many local speakers as possible. As we realized in Port Elizabeth, the standard of lectures by South African speakers was exceptionally high. I have unfortunately been booked off for a few weeks due to a spinal operation. The recovery, much to my dismay, is taking a lot longer than I anticipated. Thank you for your support. There are a number of issues that have been put on the back burner, and I do sincerely apologise for this. I am thankfully back at the office and catching up. Please enjoy this journal, as there are, as always interesting articles and a variation of topics. The SADTC awarded 8.9 CEUs. Editorially yours Axel

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IMPORTANT INFORMATION REGARDING CPD How are the CEUs calculated for the Journal? The Journal falls under Category B: (Measurable) Training and Publications: Dental Technology and related fields, sub-category B8. A maximum of 20 of the required CEUs may be obtained/claimed from this category but not more than 10 from any sub-category, with the exception of B4 which may not exceed 20 CEU’s Answer/complete multiple-choice questionnaires (MCQ) in journals, including electronic journals and or professional association News Letters with required pass mark. 70% is needed to pass and 0.2 CEU per standard page of prescribed reading and 0.2 CEU per question is awarded.

CPD via the SADTJ – Request to Council The DENTASA office has been inundated with phone calls and request from all dental technicians to be allowed to do older SADTJ issues to be able to acquire the additional CPD credits as stipulated by letters received by Council. We have sent a formal request to Council regarding the abovementioned and our correspondence was tabled at the CPD Committee meeting of the SADTC. We in addition tabled a request for Council to remove the maximum CEUs per category limitation to ensure that CPD becomes achievable and accessible to all in the profession. We are now awaiting a response from Council. We will inform you as soon as we receive an answer. Regards,

Elize Morris DENTASA Secretary The Dental Technology Association of South Africa Tel: 012-460 1155 www.dentasa.org.za SADTJ Vol 7 Issue 2

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CPD: The waiting game It is generally accepted that CPD requirements must be: • • • • • •

reasonable, achievable, fair, accessible to all (cost-effective), transparent, flexible, and

inclusive.

Measured against these categories the SADTC’s CPD requirements falls far short as the rules are draconian and very user-unfriendly towards the profession. The maximum threshold for CEUs in certain categories is a case in point. When bench marking against other councils like the Pharmacy Council, The South African Council for Social Service Professions, The South African Institute for Professional Accountants , The Actuarial Society and most importantly the HPCSA with its TWELVE professional boards, none of them have a maximum threshold for CEUs in a category. By removing the maximum CEUs per category and making it possible to obtain all the CEUs from the Journal the SADTC will go a long way in making CPD achievable and accessible to all in the profession. DENTASA also requested the SADTC to allow the technicians to complete the SADTJ questionnaires of the 2014/2015 period to make up their CEU short fall, this will also be discussed at the planned workshop. In light of the above DENTASA requested that Mariaan Roets be allowed to attend and give her valued input at their proposed workshop which was supposed to have been held in March. It is now the middle May and we are still waiting for any feedback from Council, seven months after our initial letters. Our request to publish the SADTC newsletters and annual report in order for technicians to gain Ethic and Business points by completing the questionnaires was prohibited. We regret this decision as it would have made it possible for technicians in the rural areas to earn their Ethics and Business CEUs much easier and cheaper. Half of this year is almost gone, we need clarity on the above issues, the CPD compliance rate is abysmal, let’s make it reasonable, achievable, fair, accessible, transparent, flexible and inclusive. It is possible. Ms. Roets attended the CPD workshop representing DENTASA. We suggested the following to make it easier for technicians to comply, for service providers to apply and for the Council to administer: 1. Abolish maximum threshold per category 2. Make Ethics and Business CEUs available in accredited publications and other media 3. Simplify accreditation process 4. That technicians be given a chance to get the required CEU’s for 2014/2015 by completing the 2014/2015 questionnaires in the SADTJ. The CPD Committee discussed the requests after the workshop in their meeting and will make recommendations to the Council. The next SADTC meeting is 15 July.

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J Indian Prosthodont Soc (Apr-June 2013) 13(2):83–88 DOI 10.1007/s13191-013-0260-z

ORIGINAL ARTICLE

A Comparison of the Change in Mandibular Condyle/Fossa Relationship with the Use of Anatomic Teeth and Semi-anatomic Teeth in Complete Denture Prosthesis Satyabodh S. Guttal • Ramesh K. Nadiger Abhishek Suvarna

Received: 16 January 2013 / Accepted: 14 February 2013 / Published online: 22 February 2013  Indian Prosthodontic Society 2013

Abstract The association between dental occlusion and mandibular condyle/fossa relation has long been debated and still remains one of the most controversial issues in Prosthodontics. The aim of the study was to evaluate the effect of two different tooth forms on the condyle/fossa relation recorded during jaw relation process. Twenty edentulous patients were selected with good neuromuscular control. For each patient two pairs of dentures were fabricated with anatomic teeth and semi-anatomic teeth. Condylar position was recorded using a digital volume tomography (DVT) following the process of jaw relation (following extra oral tracing). Subsequent laboratory remounting, the denture insertion was done and DVTs were taken again for both the dentures separately. Two methods were used to evaluate the condyle/fossa relation viz. (1) Zhang’s method (2) Brewka’s method. The obtained values were then subjected to statistical analysis. The statistical significance was set as at 0.05 %. The mandibular concentricity were analysed during the process of jaw relation and after the insertion of dentures with the two different tooth forms. Statistical analysis indicated that no statistically significant difference of the influence of different posterior tooth forms on the condyle/fossa relation recorded during jaw relation (p \ 0.05). Thus within limitations of this study it was concluded that the condyle/fossa relation established during jaw relation does not change with the change in posterior tooth form used. Keywords Mandibular condyle  Temporomandibular joint anatomy  Posterior tooth forms S. S. Guttal (&)  R. K. Nadiger  A. Suvarna Department of Prosthodontics, SDM College of Dental Sciences and Hospital, Dharwad 580009, Karnataka, India e-mail: drsatyabodh@yahoo.co.in

Introduction A basic knowledge of the stomatognathic system starts with the temporomandibular joint, since it is the centre of structural and functional inter-relationship. If one were to ask the one arch to arch relationship that is most important to comfort, function and health of stomatognathic system, one would definitely say without reservation, centric relation. It is impossible for one to develop a harmonious occlusal relationship without first determining that each condyle is properly aligned with its disk and the condyledisk assembly is properly positioned in its fossa in centric relation. This is the starting point of occlusion [1]. It has always been a matter of controversy for years as to why artificial posterior teeth should resemble natural teeth. Gysi [2] recognized that his anatomic teeth would not satisfy all ridge relationships and in 1927 he designed a modified ‘‘cross bite’’ posterior teeth. In this scheme, the maxillary buccal cusps were almost eliminated resulting in one prominent lingual cusp that occluded into a lower anatomic tooth. These were the earliest semi-anatomic tooth forms. This innovative departure from contemporary occlusal forms created a great controversy and touched off a trend to alter occlusal forms for masticatory efficiency, balance, or to reduce thrust. The influence of condylar position and the loss of posterior teeth on TMDs remains one of the most debatable issues, as does the influence of lost molar replacement by a removable denture. Nevertheless, some researchers have shown the importance of prosthetic rehabilitation for reducing the symptoms of TMDs [3]. Digital volume tomography (DVT) is a recent imaging technique which produces similar three dimensional images to CT but at a radiation dose comparable with panoramic radiography and a lower expense. DVT provides us

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with the option of skull imaging with high geometric accuracy in all spatial planes as well as three-dimensional reconstruction at high resolution. Until now, these options were only been available with standard CT. Although because of these recent developments it is possible with low-dose techniques to achieve a dose reduction of 76 % without losing diagnostic accuracy along with being ten times more than the effective dose of a panoramic radiograph [4, 5]. In fact compelling data explaining the relation of different types of posterior teeth on the condyle/fossa relation recorded during jaw relation is not presently available. The purpose of this study was to determine whether condyle/ fossa relation gets altered when two different occlusal forms are used in a prosthodontic rehabilitation of a complete denture patient using DVT.

Materials and Methods The study group of twenty edentulous subjects were selected (14 men, 6 women) with good neuromuscular control in the age group of 40–55 years. Since this study involved radiation exposure to the involved subjects, a written consent was obtained from each patient after full explanation of the procedure. All the subjects were examined by a same examiner. All the subjects were given a Research Diagnostic Criteria [6, 7] for TMD Questionnaire. The scores were carefully evaluated and the patients with the signs and symptoms of TMD were excluded from the study. The inclusion criteria for the study involved subjects with no history of TMD and subjects with well rounded upper and lower ridges. The exclusion criteria were temporomandibular joint pain verified by the questionnaire and clinical examination, previous treatment for TMD, or a history of psychiatric disorders or symptoms related to disease in other components of the stomatognathic system. Ethical clearance for this study was obtained from the ethical clearance committee of S.D.M College of dental sciences (ID no-2013/P/PROS/22). It would also be mentioned that this study was conducted in accordance to the principles of the Declaration of Helsinki as revised in 2000. The DVT’s of the subjects were recorded with the assigned radiologist of the institution. In order to eliminate observer’s bias, the radiologist was informed to randomize the soft copies of the DVT of the dentures with anatomic teeth and DVT of the dentures with semi-anatomic teeth and to hide the information regarding the type of denture they were wearing from the observer. All the radiographic tracings were performed by the same clinician. Routine steps were performed till final impression to get the master casts. The master casts were then duplicated

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using liquid silicone (Doublident, Hamburg, Germany). Wax rims were fabricated on the temporary denture base. Tentative jaw relations were recorded and centric relation was recorded. The terminal hinge axis was recorded using Hanau spring bow. The maxillary and mandibular casts were mounted on to the Hanau wide view articulator. Extra oral gothic arc tracers were attached to the maxillary and mandibular occlusal rims. Extra oral tracing was carried out and centric relation was confirmed. A digital tomogram was then taken during this stage to have a radiographic record of the centric relation. The casts were then remounted according to the correct centric relation. The occlusal rims were then rebuilt. A silicone putty index (Aquasil, Dentsply, Konstanz, Germany) was then made on these rims. A second set of rims were then duplicated using this index. The articulator was then programmed according to values derived from the patients protrusive bite record. Thecondylar guidance was adjusted until the protrusive record was completely seated. The Bennett angle was calculated using the Hanau formula L = H/8?12. Preparation of Dentures with Anatomic Teeth After the rims were duplicated, a teeth arrangement was done in class 1 arrangement using anatomic teeth with a cusp angle of 33 Cosmo teeth set (Cosmo, Dentsply, Tianjin, China). Uniform contacts were then in centric relation established. Waxing and carving procedures were carried out. Denture was then tried in the patient’s mouth. After a satisfactory trial procedure, the trial dentures were then processed. Laboratory remounting was done following BULL’s law. Uniform contacts were established both in centric and eccentric positions. The dentures were then inserted and minor adjustments were done. A digital volume tomogram of the two mandibular condyles was then taken during this step. It was then compared with the earlier DVT of the centric record. Preparation of Dentures with Semi-anatomic Teeth The other set of master casts and occlusal rims were used to fabricate this set of dentures. Teeth arrangement was carried out with the help of semi-anatomic teeth (Premadent, Delhi, India).The teeth were arranged in class 1 arrangement. Selective grinding was performed. After the insertion of these dentures a DVT of both the mandibular condyles were carried. These were then compared with the DVT of the centric record. Measurement of the Change in Condyle/Fossa Relation A Kodak Digital Volumetric Tomogram was used for this study. A total of six DVT’s were recorded for a patient.


J Indian Prosthodont Soc (Apr-June 2013) 13(2):83–88

Initial two DVT of the right and left condyles were taken during the jaw relation step. The other set of DVT was taken during the insertion of the dentures with anatomic teeth and the final set of DVT was taken during the insertion of the dentures with semi anatomic. For measurement of the joint space between the condyle and the glenoid fossa the method suggested by Zhang Zhenkang [8] was used (Fig. 1). Accordingly a reference line was drawn parallel with the Frankfort horizontal plane and tangent to the superior most aspect of the glenoid fossa. From the highest point of the glenoid fossa, line A was drawn perpendicular to the reference line. Line B was drawn at an angle of 45 to the line across the thinnest part of the joint. Line C was also drawn at 45 to the reference line passing through lines A and B. Line C also passes through the posterior joint space. The length of lines A, B and C between the condyle and the glenoid fossa were calculated and denoted the width of the upper anterior, superior and posterior joint spaces [6]. The centre of the condyle and the centre of the fossa were located according to method described by Brewka [9], Willis [10], and Hatjigiorgis [11] (Fig. 2). Line 1 was drawn parallel to the reference line and tangent to the highest point of the condyle. Line 2 perpendicular to line 1 and tangent to the anterior most aspect of the condyle. Line 3 was drawn parallel to line 2 and tangent to the posterior most aspect of the condyle. Line 4 was drawn parallel to line 1 and at a distance to line 1 equal to that between line 2 and line 3. These four lines intersect to form a square. The intersection point of the two diagonals of this square denoted the centre of the mandibular condyle. Line E–F was drawn parallel to the reference line and tangential to the crest of the articular eminence. The line representing the X-axis was drawn further midway between and parallel to line E–F and the reference line. The line perpendicular to the reference line at the point where the reference line intersected the height of the fossa represented the Y-axis. The point of intersection of the X- and Y-axes indicated the centre of the glenoid fossa. The distance from the centre of the condyle to the center of the glenoid fossa on the X-axis and the Y-axis was measured and recorded.

Results The statistical unpaired t test was performed. The obtained values compared were independent variables. The unpaired t test showed no statistical difference (at the 5 % level) between the values obtained from comparing the condyle/ fossa relation during jaw relation and during insertion of dentures with anatomic teeth. The results are displayed in graphic presentation (Figs. 3, 4, 5 and 6). In addition the data obtained in this by comparing the condyle/fossa

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relation during jaw relation and following insertion of dentures with semi-anatomic teeth, found that no statistical difference existed at 5 % level of significance (Figs. 7, 8, 9 and 10).

Discussion Dawson [1] stated that the combination of anterior guidance and condylar guidance determines the border path of each mandibular posterior tooth. Rugh and Johnson [12] stated that movements of the mandible were determined by the shape, relative position and anatomy of the teeth and the temporomandibular joint. They emphasized that the relationship of jaw movements to occlusal and joint anatomy was a very important clinical factor. Blanchard [13] advocated that there are two factors governing the unavoidable length of the cusps they are; (1) The inclinations of the paths of the heads of the condyles in function, (2) Varying angle of incisal guidance deemed necessary for pleasing esthetics. Steep condylar and incisal inclinations force the use of sharper angles in the central fossae of posterior teeth, which result in creation of longer points on the occlusal surfaces of the teeth when they are formed to harmonize in functional movements of the lower jaw. However the shallow inclinations in either or both of the incisal guidance and condylar paths tend to reduce the need for cuspal height, which, if excessive, results in heavy lateral thrusts that result in tilting of the dentures or overload the portions of the ridges by throwing unbalanced pressure into limited areas. Dawson [14] stated that anyone who has recorded the hinge axis using a facebow should understand that it is possible to manipulate the mandible in centric relation and the mandible would rotate around a fixed axis without translation. The fact that the mandible can rotate around a fixed axis rules out vertical dimension as a critical aspect of centric relation. On the fixed axis of centric relation the condyles tend to rotate, enabling the mandible to close and open a fair amount without moving off the axis. Thus in this study because of recording the hinge axis with the face bow the position of the condyle with respect to the glenoid fossa does not change when two different teeth sets with different cuspal angles are used. This study also substantiates the hypothesis that in centric relation the condyles are placed anterio-superiorly in the glenoid fossae and braced against the TMJ ligament and posterior surface of the eminence as is evident by the DVTs of the condyles in the centric relation. Armani et al. [3] conducted a study to analyse the condyle/fossa relationship before and after prosthetic rehabilitation with maxillary complete denture and mandibular removable partial denture. He concluded that

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Fig. 1 Calculating the joint spaces with the Zhang’s method

Fig. 2 Locating the centre of the condyle and centre of mandibular fossa using the method suggested by Brewka, Willis and Hatjigiorgis

Fig. 3 Comparison of condyle/fossa relation during jaw relation and with dentures with anatomic teeth of the left TMJ using Brewka, Willis and Hatjigiorgis’s method

Fig. 4 Comparison of condyle/fossa relation during jaw relation and with dentures with anatomic teeth of the right TMJ using Brewka, Willis and Hatjigiorgis’s method

significant changes in the condylar position occurred after prosthetic rehabilitation in subjects without symptoms of TMDs.

Alsawaf et al. [15] conducted a study to determine the influence of tooth contact on the path of condylar movements. The result of this study indicated that dynamic

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Fig. 5 Comparison of condyle/fossa relation during jaw relation and with dentures with anatomic teeth of the left TMJ using Zhangs method

Fig. 8 Comparison of condyle/fossa relation during jaw relation and with dentures with semi-anatomic teeth of the right TMJ using Brewka,Willis and Hatjigiorgis’s method

Fig. 6 Comparison of condyle/fossa relation during jaw relation and with dentures with anatomic teeth of the right TMJ using Zhangs method

Fig. 9 Comparison of condyle/fossa relation during jaw relation and with dentures with semi-anatomic teeth of the left TMJ using Zhang’s method

Fig. 7 Comparison of condyle/fossa relation during jaw relation and with dentures with semi-anatomic teeth of the left TMJ using Brewka, Willis and Hatjigiorgis’s method

Fig. 10 Comparison of condyle/fossa relation during jaw relation and with dentures with semi-anatomic teeth of the right TMJ using Zhang’s method

inter-arch tooth guidance or change in vertical dimension reflect a significant alteration in the recordings of condylar guidance.

The study had some limitations such as it did not include different occlusal patterns in the same denture base [16]. Since the sample size for this study was small (20 subjects),

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future studies can be performed on this topic with larger sample size. Also the study does not evaluate the role of different occlusal tooth forms on the condyle/fossa relations in different eccentric positions. Therefore, the further scope of this research is to evaluate the effect of two different tooth forms on the condyle/fossa relation in various eccentric positions and to perform a similar study on this topic with a larger sample size.

Conclusion Thus, within limitations of this study the following conclusions were drawn: 1

2

The condyle/fossa relation recorded during jaw relation remained the same when dentures with anatomic teeth or dentures with semi-anatomic teeth were used and does not show any significant change between the two types of tooth forms. The type of the tooth form used for processing dentures had no bearing on the condyle/fossa relation recorded during jaw relation procedure.

References 1. Dawson PE (1989) The stomatognathic system. Evaluation, diagnosis and treatment of occlusal problems, 2nd edn. The CV Mosby, St Louis, p 18 2. Winkler S (2000) Complete denture occlusion. In: Ortman HR (ed) Essentials of complete denture prosthodontics, 2nd edn. AITBS Publication, New Delhi, p 225

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3. Amorim P, Cruz Lagana0 D, de Virgilio Paula Eduardo J, LuizZanetti A (2003) Analysis of the condyle/fossa relationship before and after prosthetic rehabilitation with maxillary complete denture and mandibular removable partial denture. J Prosthet Dent 89:508–514 4. Ziegler CM, Woertche R, Brief J, Hassfeld S (2002) Clinical indications for digital volume tomography in oral and maxillofacial surgery. Dentomaxillofac Radiol 31:126–130 5. Kobayashi K, Shimoda S, Nakagawa Y, Yamamoto A (2004) Accuracy in Measurement of distance using cone beam computed tomography. Int J Oral Maxillofac Implants 19:228–231 6. Dworkin SF, LeResche L (1992) Research diagnostic criteria for temporomandibular disorders: review, criteria, examinations and specifications, critique. J Craniomandib Disord 6(4):301–355 7. Petersson AJ (2010) What you can and cannot see in TMJ imaging–an overview related to the RDC/TMD diagnostic system. J Oral Rehabil 37(10):771–778 8. Hongchen L, Jilin Z, Ning L (1992) Edentulous position of the temporomandibular joint. J Prosthet Dent 67(3):401–404 9. Brewka RE (1981) Pantographic evaluation of cephalometric hinge axis. Am J Orthod 79:1–19 10. Willis BH (1982) Tomographic study of the relationship between the mandibular condyle and glenoid fossa in patients with temporomandibular joint dysfunction [Master’s thesis]. Georgetown University, Washington DC, p 183 11. Hatjigiorgis C (1987) GA tomographic study of the temporomandibular joint of edentulous patient. J Prosthet Dent 57: 354–358 12. Rugh JD, Johson RW (1988) Mandibular movements. In: Mohl ND, Zarb GA, Carlsson GE, Rug JD (eds) Textbook of occlusion, 1st edn. Quintessence, Chicago, pp 129–141 13. Blanchard CH (1951) Some phases of our many-denture problem. J Prosthet Dent 1(5):523–542 14. Dawson PE (1985) Optimum TMJ condyle position in clinical practice. Int J Periodontics Restorative Dent 5:10–31 15. Alsawaf M, Grapplo DA (1992) Influence of tooth contacts in path of condylar movements. J Prosthet Dent 67(3):394–400 16. TrapOzzano VR, Lazzari J (1952) An experimental study of the testing of occlusal patterns on the same denture bases. J Prosthet Dent 2(4):440–457


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J Int Soc Prev Community Dent. 2015 Sep-Oct; 5(5): 365–371. doi: 10.4103/2231-0762.165928 PMCID: PMC4606599

Do flexible acrylic resin lingual flanges improve retention of mandibular complete dentures? Ayman Elmorsy Ahmed Elmorsy, Eman Mostafa Ahmed Ibraheem,1 Alaa Aboul Ela, Ahmed Fahmy, and Mohammad Zakaria Nassani2 Corresponding author (email: <massssani@hmsiail.iim>) Dr. Mohammad Zakaria Nassani, Department of Restorative Dental Sciences, Al-Farabi Colleges, PO Box 85184, Riyadh - 11691, Saudi Arabia. Copyright : Š 2015 Journal of International Society of Preventive and Community Dentistry This is an open access article distributed under the terms of the Creative Commons AttributionNonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

Abstract INTRODUCTION Despite the current decline in the rate of complete edentulism,[1,2] the need for complete denture treatment will probably continue.[3] Thus, research and efforts to improve the outcome of treatment with complete dentures should also continue. Prosthodontists and general dental practitioners recognize that wearing complete dentures is troublesome for some patients and associated with a wide range of problems. However, complaints related to complete denture retention and stability are the most frequent.[4] Such problems become even worse with mandibular dentures due to a number of anatomical and physiological factors.[5] Unsatisfactory denture retention has its implication on the prognosis of treatment with complete dentures. Oral discomfort, defective speech, difficulty during chewing, and irritation of the supporting tissues are examples of the problems that

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are associated with inadequate denture retention. It was also found that patientsâ&#x20AC;&#x2122; use and satisfaction with complete dentures is highly dependent on the quality of denture retention.[6,7] Many authors provided tips and recommendations for dentists to improve the quality of complete denture retention.[8,9,10] Also, denture adhesives and dental implants were used to enhance denture retention. One possible and simple way of enhancing denture retention is by extension of denture flanges to engage an existing soft-tissue undercut.[11,12] However, extension of conventional denture bases into soft-tissue undercuts should be kept minimal due to rigidity of acrylic resin. The introduction of resilient denture liners[13] and flexible acrylic resin[14] increased the chance for denture bases to be extended into deeper soft-tissue undercuts to gain further retention without risking the health of the supporting tissues or creating pain and difficulty during denture removal or insertion. Some authors reported the use of permanent soft liners in the retromylohyoid eminence to aid denture retention.[15,16] Lowe[17] used flexible acrylic resin to create flexible denture flanges for patients exhibiting undercut tuberosities. This technique can also be used to aid retention of mandibular complete dentures by creating flexible lingual flanges that engage the lingual undercuts of the mandible. However, it is not yet clear from the current literature to what extent would denture retention be improved by the use of flexible acrylic resin in fabrication of the lingual flanges of mandibular complete dentures. The aim of this study was to examine the hypothesis that there is no significant difference in the retention force between mandibular dentures of conventional construction and mandibular dentures constructed with flexible acrylic resin lingual flanges. MATERIALS AND METHODS This study was approved by the Research Ethics Committee of Faculty of Oral and Dental Medicine, Cairo University, Egypt. Patient selection

Ten completely edentulous patients were selected from the out-patient clinic of the Removable Prosthodontics Department, Faculty of Oral and Dental Medicine, Cairo University. All patients were presented with explanation about the objectives, implications, and possible complications of this study and invited to sign an informed consent. The inclusion criteria were as follows: ď&#x201A;ˇ

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Completely edentulous male patients

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     

Age range between 45 and 65 years Patients having had no previous complete dentures Patients who had their last remaining teeth extracted at least 3 months before recruitment in the study Patients with well-developed edentulous ridge that was covered with healthy firm mucosa Patients with normal Angle Class 1 maxillomandibular relationship Patients who were free from systemic diseases that affect the neuromuscular control, such as Parkinson's disease.

The exclusion criteria were as follows:  

Patients with resorbed ridges Patients with xerostomia and patients undertaking medications that affect salivary flow (e.g., diuretics). Similarly, patients with systemic diseases that may affect the amount or consistency of saliva (e.g., uncontrolled diabetes mellitus) were excluded.

Construction of the dentures

Complete dentures were provided by the first author in the Department of Removable Prosthodontics, Faculty of Oral and Dental Medicine, Cairo University. One expert dental technician constructed all the dentures. Before construction of the dentures, full medical and dental history was taken from each patient, following which an extraoral and intraoral examination and an orthopantomogram (OPG) were performed. Complete dentures were constructed for each patient following the guidelines of the British Society for the Study of Prosthetic Dentistry.[18] Each patient received one maxillary denture and two mandibular dentures. One mandibular denture was made entirely of conventional heat-cured acrylic resin and the other mandibular denture was made of conventional heat-cured acrylic resin with thermoplastic flexible acrylic resin “Versacryl” (Keystone Industries GmbH, Sigen, Germany) at the lingual flange area. Primary impressions were made by irreversible hydrocolloid alginate impression material (Cavex alginate, dust free, high consistency; Cavex Holland BV, Haarlem, Netherlands) using perforated stock trays. Self-cured acrylic resin (cold cure denture base material; Acrostone, Cairo, Egypt) special trays were constructed for making the secondary impressions. The special trays were trimmed 2 mm short of the tissue reflection area and checked for border extension and adaptation inside

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the patient's mouth. The secondary impressions were taken using putty and medium addition type rubber base impression material (Speedex, Coltène/Whaledent Company, Altstätten, Switzerland). In the first step of making the secondary impression, the putty body rubber base impression material was used for border molding following the conventional methods and the manufacturer's instructions. The medium body rubber base impression material was used to make a wash impression in the second step of making the secondary impression. The lower secondary impressions were boxed and poured twice to obtain two stone master casts in order to construct two sets of dentures. At the wax-up stage of the mandibular dentures, the lingual flanges for both types of dentures were designed to engage 2 mm of the undercut area of the mylohyoid ridge. At the insertion appointment, patients were provided with verbal and written instructions about how to deal with their new dentures. Figure 1 shows a mandibular complete denture with flexible acrylic resin lingual flanges after processing and finishing. Allocation of patients

This study implemented a cross-over design. The selected patients were randomly allocated to two equal treatment groups, with five patients in each group as follows: 

Group 1: Patients in this group received conventional maxillary and mandibular complete dentures. The patients used these dentures for 45 days. Then, the conventional lower denture was replaced by one with flexible lingual flanges. The same patients were followed up again for 45 days Group 2: Patients in this group received a conventional maxillary complete denture and a mandibular complete denture with flexible lingual flanges. The patients used these dentures for 45 days. Afterward, the lower denture with flexible lingual flanges was replaced by one with a conventional construction. The same patients were followed up again for 45 days.

Follow-up of patients

With each type of mandibular denture, the patient was followed up for 45 days. At each review appointment, patient's complaints were noted. The supporting tissues, the denture surfaces and borders, the occlusion and articulation of the dentures, were all examined. Then the dentures were adjusted in the light of clinical examination and patient's complaints. Retention of dentures was assessed and recorded during the follow-up period.

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Assessment of denture retention

In both groups, retention of mandibular dentures was tested at the time of delivery and at 2 weeks and 45 days following denture insertion. A digital force-meter (Extech instruments 475040, Nashua, New Hampshire, USA) was used to measure denture resistance to vertical displacement (i.e., retention) by applying a pulling force on a metal hook located in the geometric center of each mandibular denture. Based on geometrical principles,[19] identification of the geometric center for each mandibular denture was carried out as follows:    

All undercuts in the fitting surface of the denture were blocked by base plate wax A mix of plaster was then poured into the fitting surface of the denture and another mix was used to construct a base The centers of the retromolar pads and the midline were marked on the polished surface of the denture [Figure 2] In the next step, a cardboard was cut out so as to form a triangle which was placed on the plaster base to occupy the space in between the three aforementioned markings Three lines bisecting the three angles of the triangle were then drawn on the cardboard. The intersection of these three lines was considered the geometric center of the denture [Figure 3] Following the former step, a pin was passed through the cardboard at the identified geometric center to mark a point on the plaster base. A plastic rod was then fixed to the base and suspended upward from the marked point to maintain the location of the geometric center.

Three “V” shaped grooves were created on the polished surface of the lower denture. One was made on the lingual flange at the midline region just below the central incisors. The other two grooves were created at the retromolar pad area just distal to the second molar of both sides. A wrought wire of 1 mm in diameter was then bent at its center and adjusted so as not to encroach on the tongue space and to run 2 cm above the occlusal plane from the retromolar pad groove of one side to the retromolar pad groove of the other side. Afterward, a second wrought wire of the same diameter was adjusted to extend from the groove at the lingual flange upward, so that it is 2 cm above the occlusal plane.

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mandibular dentures with flexible lingual flanges. The statistical test indicated that retention of dentures with flexible lingual flanges was significantly higher than retention of conventional dentures at the different follow-up appointments (P < 0.05). In order to examine the effect of follow-up time on the retention force of conventional mandibular dentures and dentures with flexible lingual flanges, oneway analysis of variance (ANOVA) followed by pair-wise Newman–Keuls posthoc tests were used. The statistical analysis showed that in both types of dentures, retention force after 45 days recorded significantly the highest mean value (P <0.05), whereas retention force at the time of denture delivery was significantly the lowest (P < 0.05). DISCUSSION The provision of a retentive and stable denture can be considered the principal goal of general dental practitioners when dealing with complete dentures. Research findings indicate that retention and stability of mandibular complete dentures are strong determinants of patients’ satisfaction with newly delivered dentures.[7] Extension of the lingual flanges of the mandibular denture to engage the sublingual undercut of the mandible was used and recommended as a mean to maximize retention of mandibular complete dentures.[11,12,20,21] While acrylic resin is the most commonly used denture base material, this study reported the use of flexible acrylic resin “Versacryl” to construct the lingual flanges of mandibular complete dentures. The flexible acrylic resin was introduced first in 1950 as an alternative to conventional acrylic resin denture base material.[14,22] It is a flexible biocompatible thermoplastic denture base material with unique physical and esthetic properties. The flexible acrylic can create any part of a denture to be made adjustable, simply by using warm water to soften the material so as to conform to the contours of the soft and hard tissues. Also, the flexible acrylic can be extended into undercut areas to mechanically retain the denture. Interference with soft tissue undercuts would be facilitated by the use of flexible acrylic flanges so that the denture base can be inserted and removed smoothly. Furthermore, the softness of flexible acrylic imparts a feeling of comfort to the patient.[14] However, the flexible acrylic has a number of disadvantages[23,24] and may lose the desired flexibility in the long term. Many brands of thermoplastic or flexible denture materials are available in the market, such as Valplast (Valplast Int. Corp., Westbury, New York, USA), Flexiplast (Bredent, Senden, Germay), Flexite (The Flexible Company, Mineola, New York, USA), and Lucitone® FRS™ (DENTSPLY International, Woodbridge,

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Ontario, Canada). In this investigation, Versacryl (Keystone Industries GmbH, Sigen, Germany) was used as a thermoplastic material to construct the lingual flanges of the mandibular complete dentures. Versacryl has the physical properties of the thermoplastic materials, as indicated by the manufacturer. When inserted and adapted to the mouth after immersion in warm water (50°C) for 5 min, Versacryl will cool to body temperature and take on the desired rigidity to fulfill its function.[25] Despite the relatively old age of the thermoplastic denture base materials, reports to evaluate its impact on denture retention are scarce. Antonelli and Hottel[26] reported the use of flexible acrylic flanges to construct stable, retentive, welladapted, and comfortable complete dentures record bases. Singh et al.[27] found that flexible denture bases produced better patient satisfaction and comfort, compared to conventional acrylic resin denture bases. In this clinical study, the use of flexible lingual flanges in the construction of mandibular complete dentures has resulted in improved denture retention, compared to conventionally made dentures with acrylic resin flanges. This may be attributed to the physical properties of the flexible acrylic which allowed effective engagement with the lingual pouch undercut and close adaptation to the supporting tissues.[14,27] It can be argued that an intimate adaptation of the flexible denture flanges to the underlying tissues with the existence of a thin film of saliva in between the two objects would increase the effectiveness of adhesion forces and enhance the peripheral seal around the denture borders.[8,28] Thus, effective mechanical and physical factors interplayed to produce better retention for mandibular complete dentures with flexible acrylic resin flanges. However, this is a short-term study and further studies are recommended to evaluate the long-term quality of retention of mandibular complete dentures with flexible lingual flanges and its impact on patientsâ&#x20AC;&#x2122; satisfaction. Finally, it can be noted that over the follow-up period, there was an improvement in denture retention for both types of dentures. This finding can be explained by the improved fit of the denture bases due to the medium-term remodeling of the soft tissues underlying the dentures in order to maintain the mucosal contact with denture bases.[28] CONCLUSION The use of flexible acrylic resin lingual flanges in the construction of mandibular complete dentures resulted in improved denture retention. The hypothesis that there was no significant difference in retention force between mandibular dentures

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of conventional construction and mandibular dentures constructed with flexible acrylic resin lingual flanges was, therefore, rejected. Financial support and sponsorship

Nil. Conflicts of interest

The authors declare no financial relationship with any commercial firm that may pose a conflict of interest for this study. REFERENCES 1. Wu B, Liang J, Landerman L, Plassman B. Trends of edentulism among middleaged and older Asian Americans. Am J Public Health. 2013;103:e76–82.[PMCID: PMC3780672] [PubMed: 23865668] 2. Slade GD, Akinkugbe AA, Sanders AE. Projections of U.S. Edentulism prevalence following decades of decline. J Dent Res. 2014;93:959–65.[PMCID: PMC4212322] [PubMed: 25146182] 3. Douglass CW, Shih A, Ostry L. Will there be a need for complete dentures in the United States in 2020? J Prosthet Dent. 2002;87:5–8. [PubMed: 11807476] 4. Bilhan H, Geckili O, Ergin S, Erdogan O, Ates G. Evaluation of satisfaction and complications in patients with existing complete dentures. J Oral Sci. 2013;55:29– 37.[PubMed: 23485598] 5. Ribeiro JA, de Resende CM, Lopes AL, Farias-Neto A, Carreiro Ada F. The influence of mandibular ridge anatomy on treatment outcome with conventional complete dentures. Acta Odontol Latinoam. 2014;27:53–7. [PubMed: 25523954] 6. Fenlon MR, Sherriff M, Walter JD. An investigation of factors influencing patients’ use of new complete dentures using structural equation modelling techniques. Community Dent Oral Epidemiol. 2000;28:133–40. [PubMed: 10730722] 7. Fenlon MR, Sherriff M. An investigation of factors influencing patients’ satisfaction with new complete dentures using structural equation modelling. J Dent. 2008;36:427–34. [PubMed: 18417267] 8. Jacobson TE, Krol AJ. A contemporary review of the factors involved in complete denture retention, stability, and support. Part I: Retention. J Prosthet Dent. 1983;49:5–15. [PubMed: 6337253]

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9. McCord JF, Grant AA. Identification of complete denture problems: A summary. Br Dent J. 2000;189:128–34. [PubMed: 11041628] 10. Scott BJ, Hunter RV. Creating complete dentures that are stable in function. (265-7).Dent Update. 2008;35:259–62. [PubMed: 18557503] 11. Bocage M, Lehrhaupt J. Lingual flange design in complete dentures. J Prosthet Dent. 1977;37:499–506. [PubMed: 321762] 12. von Krammer R. Principles and technique in sublingual flange extension and complete mandibular dentures. J Prosthet Dent. 1982;47:479–82. [PubMed: 7045334] 13. Soni A. Management of severe undercuts in fabrication of complete dentures. N Y State Dent J. 1994;60:36–9. [PubMed: 7936493] 14. Rickman LJ, Padipatvuthikul P, Satterthwaite JD. Contemporary denture base resins: Part 2. (180-2).Dent Update. 2012;39:176–8. 184 passim. [PubMed: 22675889] 15. Whitsitt JA, Battle LW, Jarosz CJ. Enhanced retention for the distal extensionbase removable partial denture using a heat-cured resilient soft liner. J Prosthet Dent. 1984;52:447–8. [PubMed: 6384483] 16. Mendez M, Lee C. Use of a permanent soft denture liner in the retromylohyoid eminence and knife-edge ridge areas of the mandible to aid in retention and stability. Gen Dent. 2013;61:e14–5. [PubMed: 24192741] 17. Lowe LG. Flexible denture flanges for patients exhibiting undercut tuberosities and reduced width of the buccal vestibule: A clinical report. J Prosthet Dent. 2004;92:128–31. [PubMed: 15295320] 18. Ogden A. London: Quintessence Publishing Co. Ltd. for the British Society for the Study of Prosthetic Dentistry; 1996. BSSPD Guidelines in Prosthetic and Implant Dentistry; pp. 7–11. 19. Weisstein EW. “Geometric Centroid.” MathWorld--A Wolfram Web Resource. [Last accessed on 2015 July 31]. Available from:http://mathworld.wolfram.com/GeometricCentroid.html . 20. Azzam MK, Yurkstas AA, Kronman J. The sublingual crescent extension and its relation to the stability and retention of mandibular complete dentures. J Prosthet Dent. 1992;67:205–10. [PubMed: 1538327]

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21. Chang JJ, Chen JH, Lee HE, Chang HP, Chen HS, Yang YH, et al. Maximizing mandibular denture retention in the sublingual space. Int J Prosthodont. 2011;24:460–4. [PubMed: 21909488] 22. Price CA. A history of dental polymers. Aust Prosthodont J. 1994;8:47– 54. [PubMed: 8611309] 23. Sunitha NS, Jagadeesh KN, Kalavathi SD, Kashinath KR. ”Flexible dentures” An alternate for rigid dentures? J Dent Sci Res. 2010;1:74–9. 24. Sharma A, Shashidhara HS. A review: Flexible removable partial dentures. J Dent Med Sci. 2014;13:58–62. 25. Keystone Industries. [Last accessed on 2015 July 31]. Available from: https://keystoneind.wordpress.com/tag/versacryl/ 26. Antonelli JR, Hottel TL. The “flexible augmented flange technique” for fabricating complete denture record bases. Quintessence Int. 2001;32:361– 4.[PubMed: 11444067] 27. Singh JP, Dhiman RK, Bedi RP, Girish SH. Flexible denture base material: A viable alternative to conventional acrylic denture base material. Contemp Clin Dent. 2011;2:313–7. [PMCID: PMC3276859] [PubMed: 22346159] 28. Darvell BW, Clark RK. The physical mechanisms of complete denture retention. Br Dent J. 2000;189:248–52. [PubMed: 11048392] Figures and Tables Figure 1

The mandibular complete denture with “Versacryl” lingual flanges

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Figure 2

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The mandibular complete denture with â&#x20AC;&#x153;Versacrylâ&#x20AC;? lingual flanges Figure 2

The markings on the mandibular denture Figure 3

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The markings on the mandibular denture Figure 3

Identification of the geometric center of the mandibular denture on the cardboard (arrow) Figure 4

(a and b) The second wire adjusted to meet the first wire at the geometric center with its free end bent into a c-shaped loop

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Figure 5

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(a and b) The second wire adjusted to meet the first wire at the geometric center with its free end bent into a c-shaped loop Figure 5

Clinical evaluation of denture retention by a digital force-meter Table 1

Mean and standard deviation of retention force measured in grams for study groups with both denture materials at different follow-up periods

Articles from Journal of International Society of Preventive & Community Dentistry are provided here courtesy of Medknow Publications

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PAYSLIPS ARE IMPORTANT! PAYSLIPS ARE IMPORTANT! A PRACTICAL GUIDE TO GETTING THEM RIGHT A PRACTICAL GUIDE TO GETTING THEM RIGHT Getting payslips correct for your staff carries legal responsibilities for both you and the staff member.

Payslips are of correct course often used staff in thecarries public domain, such as for getting and so they are a Getting payslips for your legal responsibilities forbank bothloans, you and the staff public Payslips are of course reflection of your member. often used in the public domain, such as for getting bankbusiness. loans, and so they are a public reflection of your business. What to look for in a payslip What

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There are many items to verify and check: 1.

The employee’s name and job title (if one is specified). The employer’s name must be the same as the one the employee contracted with.

2.

The salary paid is as per the letter of employment and subsequent annual earnings announcements.

3.

Pay careful attention to deductions, particularly tax deductions. If they are incorrect, SARS will look to employees and employers to make good any shortfalls which could attract penalties. Good employers will have satisfied themselves that fringe benefits are lawful and will withstand any scrutiny from SARS. Employees should similarly satisfy themselves to avoid paying in extra tax and penalties. The UIF deduction is small but can help laid off workers, and should be agreed to Department of Labour tables. Bonuses should be tied up to correspondence with the employer.

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Retirement funding - 27.5% of a salary package is tax deductible. If this is incorrect, it can adversely impact retirement amounts (don’t forget the power of compounding over the years). In the event of untimely death, payouts to family members could be affected.

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Other deductions, such as repayment of loans should be checked against the loan agreement.

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Garnishee orders. Remember that since September 2016, garnishee orders need to be approved by a Magistrate (no longer a Clerk of the Court) who must be satisfied that the order is fair, equitable and affordable. Ensure the order has been approved and the amount deducted on the payslip is as per the garnishee order.

Getting payslips right will save both you and your employee time and frustration – no one wants to get into afterthe-fact arguments with SARS or retirement funders. The employer/employee relationship involves trust on both sides and errors on payslips could jeopardise this.

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Printed with permission from the “Dental Technology Journal” JDt teChniCal

Making Friends with Your sintering oven

heating elements By John Davis

“That” Type of Consumable

w

e have all had that moment — where the essential tool in the shop or office suddenly needs a replacement something-or-other that costs a surprising amount of money. As someone with a hobby habit (to put it lightly), my personal essentials range from the relatively esoteric — cutting tools/blades (looking at you, planer knives) to one of the usual suspects — desktop printer ink.

As dental laboratory folks, perhaps a more apropos analogy is already sitting on your desk or bench — your sintering oven. Although it is a common, everyday item, the MoSi2 heating elements inside that give it its high-temperature qualities are anything but ordinary. They are highly engineered marvels of material science — definitely “that” type of consumable. That said, you don’t have to be a heating systems expert to get the most out of your heating elements. Just like me and my woodworking, a bit of information goes a long way toward the improvement of the final product. Let’s just hope your dental castings turn out better than my furniture.

A Quick Primer on MoSi2 Elements In general, resistive heating elements scale in complexity and cost according to their temperature. For basic heating applications — such as a toaster — simple metallic wire that has favorable properties in the 500°F-800°F range is typically chosen. Similarly, these types of wires are also commonly used for lower temperature industrial heating applications (below 800°F). Broadly categorized as “Ni-Chrome” wire or NiCr, this resistance wire is a mixture of nickel and chromium; the latter forms a protective oxide layer on the surface of the

nickel, allowing it to last for a long time under (relatively) high temperatures. Up to about 2230°F (1200°C), metallic elements of varying grades and compositions are a viable option. Beyond 1200°C, things start to get a bit more interesting. In the temperature ranges required for zirconia or cobalt chromium sintering, silicon carbide (the subject of a forthcoming article) and MoSi2 are the only materials from which elements can be made and still have acceptable longevity and performance characteristics such as low spallation/flaking (useful when considering the cosmetic appearance of the sintered item — more on this later).

36 Journal of Dental Technology March 2017

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MoSi2 elements are made out of molybdenum and silicon; the latter, similar to the NiCr example above, forms a protective oxide layer on the molybdenum. In an air atmosphere, molybdenum vaporizes when heated above a certain point. The utility of the oxide layer goes without saying. MoSi2 elements are typically graded by their maximum element temperature in Celsius — 1700°, 1800°, and 1900° (and HT). The latter grade is specific to sandvik/kanthal elements and is designed specifically for high temperature/highly cyclic applications. A common error when specifying MoSi2 elements — though this applies to all heating elements as well — is specifying an element grade based on the process temperature only, not taking into consideration element temperature. In general, furnace elements must run approximately 50°C hotter than the process temperature in order to maintain a given set point. In the world of heating elements, surface loading — measured as Watts per square inch — directly influences element life. The relationship between element life and surface loading is non-linear. Once an element is powered past approximately 80 percent of its maximum surface loading, life is dramatically reduced. So, even a temperature delta as low as 50°C can have big implications. Depending on your furnace, if you are sintering at 1600°, 1700° grade elements may be fine. If you are sintering at 1650°, you will want to use 1800° grade elements to achieve maximum element lifespan.

A Note on Zirconia Discoloration One of the more common issues I hear from dental sintering folks who use MoSi2 elements is discoloration of their sintered zirconia product. Broadly, the discoloration is caused by contaminants bonding with the zirconia. More specifically, the discoloration is caused primarily by iron and molybdenum leaching out of the elements and into the furnace environment. Preventing iron leaching is a relatively straight forward process — don’t buy cheap MoSi2 elements!

Sarcasm aside, this is a good guideline to follow. All MoSi2 elements will have trace amounts of iron present as a contaminant, but the best and most pure elements will relegate iron to trace amounts rather than problematic amounts. As the saying goes — you get what you pay for. The fact of the matter is that high-purity MoSi2 elements are difficult — and relatively expensive — to manufacture. There are only a handful of reputable manufacturers in the world for these types of elements and it has taken decades to perfect the manufacturing of high-purity MoSi2 heating elements. As far as molybdenum contamination goes, this one is a bit trickier. MoSi2 heating elements form a protective silicon oxide layer. These two materials work well together, but there is a bit of an inherent challenge in highly cyclic applications such as dental sintering, since silicon heats and cools at a different rate than molybdenum (they have different coefficients of thermal expansion). Over time, the silicon builds up on the surface of the molybdenum and as it grows thicker, it begins to crack and flake off of the element and into the furnace environment. As the silicon flakes, trace amounts of molybdenum come along with it, causing contamination. There are solutions in the marketplace — super-high purity elements designed specifically to form thinner oxide layers in highly cyclic applications — that can be explored to combat this issue. Alternatively, using elements that are rated several temperature grades higher than the process temperature may also help.

Discoloration is caused primarily by iron and molybdenum leaching out of the elements and into the furnace environment.

Best Practices for Extending the life of MoSi2 Heating Elements In a perfect world, MoSi2 elements in continuous applications (no cycling to ambient temperature and back to process temperature) can expect two to three years of life. In the dental furnace world, things are a bit worse as cycling exacerbates the oxide growth and subsequent flaking issue. That said, dental laboratories should be expecting 12-18 months of life out of their elements, maybe shorter,

Zirconia Discoloration March 2017 Journal of Dental Technology 37

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Oxidized Terminal Strap

maybe longer, depending on how much the furnace is utilized and what grade of element is being used. In general, here are five things that any dental laboratory sintering operation can do to help extend element life: 1. order terminal straps and clips with each new element. The straps that come with your elements are braided aluminum. Over time, these straps oxidize (a tell-tale sign of this is the formation of what looks like frosting on the straps), and as the oxide layer spalls/ flakes off the straps, the formerly snug connection between the element terminals and the straps becomes progressively looser. The resulting gap becomes the perfect spot for arcs to form between the terminal and the terminal strap which, over time, eats away at the terminals and causes premature element failure. 2. ensure that the terminal shanks are insulated, but able to move independently. Like anything that is heated, MoSi2 elements need some freedom to move as they naturally expand and contract during heating and cooling cycles. Although the elements are able to produce a tremendous amount of power at high temperatures, they are mechanically fragile. In many respects, handling them is akin to handling glass. A common error is to use “two

Happy Terminals

shank” element holders — they hold both element terminals together in a rigid block, leaving no room for movement. Our recommendation is to use single shank holders. Also, make sure to use the correct terminal strap length. Straps that are too long — or too short — can place stresses on the terminals, also causing breakage. 3. double-check your element temperature rating and consider moving up a grade. Back to the element surface loading discussed earlier in this article: moving up a temperature grade (from 1700° to 1800°, for example), provides greater operating headroom as the element temperature is a lower percentage of the element maximum temperature. In turn, this could significantly lengthen element lifespan. For common sintering applications at 1600°C, making the jump from 1700° to 1800° grade elements is a small enough price delta that the improved element lifespan typically provides a quick enough ROI to justify the switch. 4. If you are getting less than one year of life, or are looking for maximum life, consider trying elements made specifically for dental sintering. There is no way around it, specialized elements are expensive. But they do make

a difference. High-tech elements such as Kanthal Super 1900 HT — that are engineered to manage oxide growth — have a proven track record in the market. 5. Consult an expert! High temperature heating elements are not a commodity. MoSi2 and SiC elements are an integral part of the engineered system that is your sintering furnace. Contact an expert to make sure that you are getting the best life and the best results from this highly precise system. We live and breathe heating elements — drop us a line anytime.

About the Author John Davis is the owner and founder of Dental Furnace Elements, a website dedicated to selling high-quality heating elements for the dental sintering industry. Find us at www.dentalfurnaceelements. com.

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JDt Feature

Time to Take off the Rose-Colored Glasses

Printed with permission from the “Dental Technology Journal” SADTJ Vol 7 Issue 2

37


sometimes when it comes to maintaining

Product Consistency & Quality i n t he Laboratory what you think you see isn’t necessarily what you get.

ven with standards and processes in place, there is significant room for employee misinterpretation or perhaps the processes haven’t been fully vetted. A certain protocol may have been instituted for step one, yet the repercussions of that decision could have a negative impact on step four. This is where an honest assessment of quality control is imperative. Each step within production is analyzed and maximized to achieve its fullest potential and the steps are also examined as a whole in order to ensure cohesive and efficient movement as a product travels throughout the laboratory. Quality control is an important element to a business of any size. It has seen extensive growth and honing throughout the decades and continues to develop to this day; the same as it should continue to evolve in your laboratory. According to the American Society for Quality (asq.org), the factory system, with an emphasis on product inspection, started in Great Britain in the mid-1750’s and grew into the Industrial Revolution in the early 1800’s.* In the early 20th century, manufacturers began to include quality processes in quality practices. Quality in the factory system was ensured through the skill of laborers divided into specialized tasks supplemented by audits and/or inspections. By the 1970s, U.S. industrial sectors such as automobiles and electronics had been broadsided by Japan’s high-quality competition, which represented the new “total quality” approach. Rather than relying purely on product inspection, Japanese manufacturers focused on improving all organizational processes through the people who used them. As a result, Japan was able to produce higher-quality exports at lower prices, benefiting consumers throughout the world. The U.S. response, emphasizing not only statistics but approaches that embraced the entire organization, then became known as total quality management (TQM). In the earlier days of factory quality control, if a defective product reached the customer, it might be more common for managers to ask the inspector, “Why did we let this get out?” rather than to ask the

production manager, “Why did we make it this way to begin with?” This is a provocative question that also deserves careful consideration and application in today’s lab. How can you best identify, address and remove the quality control misnomers you may have in your lab? How can you best apply quality control concepts within your lab? Read more about the different perspectives from different lab sizes.

Lab size: smaLL

D

start at the Beginning

aniela Hendrickson, CDT, a past president of NADL, has owned Northwest Ceramics, Inc. located in Columbus, Ohio, since 1986. From the beginning, she has focused on giving individual attention to every case in order to fabricate the highest quality cosmetic restorations. For her lab size, quality control starts with her when receiving the initial case or file. Hear more on how she applies QC in her lab. In my opinion, the first step is the most important step to avoid going down the wrong path to “catching it later” and costing me more money. I personally review the prescription or file for details and a technician reviews the impression before moving forward. This step should be handled by

Daniela Hendrickson, CDT "if they start on something, they own the problem, so bringing it to my attention first works better for everyone."

June/July 2016 Journal of Dental Technology 19

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Northwest Ceramics, inc., Columbus, Ohio

someone in the lab who has a complete overview of the process, not just someone who is entering the case on the computer for production. Too many times, it gets entered incorrectly which is the first downward step.

succeed through Failure

Jerry ulaszek, CDT, Te "We follow the edwards Deming model of not inspecting quality into a product but building quality into a product."

I was completely frustrated with having to call dental offices too frequently to request basic information such as pre-treatment models for anterior cases, shades not listed or unspecified materials. It took so much of my time and was chronic with some offices. So I had this brainy idea of printing a “check list” (to include with the cases). It looked very professional and I sent to my doctors to complete and include with their cases. Sounded like a good idea at the time, but I ended up calling because they forgot the checklist! Total fail! I also stopped having staff meetings to discuss “issues.” It turned in to a “complaint session” and no one felt good, including me. Now I address issues as they occur, not later, and try to have a lunch and learn (CE) session instead.

encourage independent QC

What has been really successful? Getting my technicians involved with seeing issues before they start working on a case. It’s been very helpful in stopping that snowball effect and makes me a happier person to work with. I really don’t like an atmosphere of crisis management. If they start on something, they own the problem, so bringing it to my attention first works better for everyone.

alone time

Sometimes I get so busy that I’ve stopped “spotchecking” as much as I would like. It’s something I do when I’m alone in the lab and I can focus on specific areas with the products and workflows that need improvement such as simple things, like contacts, occlusion, metal thickness, digital design changes, case pans backing up, etc. I can address those specifics in what I can change for the better. I will go over product issues with the individual technicians by showing them what I would like to see modified.

Lab size: meDium - LaRGe

J

set the Bar

erry Ulaszek, CDT, TE, is the owner of Artistic Dental Laboratories, CDL, DAMAS, in Bolingbrook, Ill., and is also serving as NADL’s president-elect. As an owner he has always taken full responsibility for setting clear expectations on exactly what he wants and he details some of his processes below. Different labs have different levels of quality; one size does not fit all. Part of that is based upon the price you are charging, with certain prices comes certain expectations. Once that has been established it needs to be expressed to the employees that these are the expectations at this particular

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step. Employees want to know what they need to do to ensure a good job and then be coached on how to get there. Another key aspect is to place people in the correct position to succeed and let them know if they are not meeting expectations. It’s important to be honest about their results.

Critical to Quality

Our current QC process is built on critical to quality steps. Each process has a point that must be done exactly correct because after that point, it can’t be corrected. We call that point critical to quality and these steps are written down in our criteria. We follow the Edwards Deming model of not inspecting quality into a product but building quality into a product. Each process has at least one critical to quality step identified; for example after you pour a model there can’t be bubbles. The technician, manager and department are aware of it and before a product leaves that department the steps are verified or else it gets kicked back.

Quantifiable Criteria

There are always going to be ‘unforced errors’ where someone just wasn’t paying attention or a machine got out of calibration. We now have documented five quantifiable criteria for each department

and we use these criteria to judge the steps that are taken which are then tabulated and included on an internal remake report each week. Every department has a different emphasis and a different acceptable error rate. The more subjective a department is, the higher the error rate. The remake reports are posted so everyone can see how they are doing. We also have a bonus system and if the department hits their acceptable error rate additional money is added to their Christmas bonus. In order to make sure they are always striving I keep adjusting the error rate until the equilibrium is found. I want them to be winners over 75% of the time. This system also points out where to focus our education.

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Be realistic

No one has 100% success rate when it comes to quality control. But you never know if it will work until you try. I first developed 15 criteria and discovered we got lost in it and ended up spending more time tabulating than achieving results. We have now refined our system. It’s also important to be honest with yourself and your employee evaluations. Some technicians may never master the skill set to be successful in that position. It’s your job to put them in a position to succeed.

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Lab size: LaRGe

V

"You need to find the system that works for a lab of your size and be willing to adapt if it doesn’t work."

Vinni abate, CDT,

the QC room

inni Abate, CDT, is an owner of York Dental Laboratory in Branford, Conn. Their quality control systems are very advanced and have taken a lot of time and money to build and put into place. Abate discusses the great lengths that his laboratory has taken to incorporate high-quality QC. We have a QC room that is divided between removables, fixed, implant and crown and bridge. For each of these departments there is a team of three CDTs that check the doctor’s preferences and then each product has to be double-QC’d by at least two of the three in that department before the final restoration leaves the laboratory. We also don’t use a microscope, we use a scanner. The product is placed and it’s blown up on a big screen which enables us to see everything on a much larger scale. We establish tolerances of what’s acceptable and what isn’t and go from there. Before it even gets to the QC room, when the case comes in we have two people that evaluate if the impressions are good before distributing to the correct department. From there we use the PTC model and have a QC protocol that needs to be signed off on before it can go to the next step. We also utilize a bar code that notifies that it has been checked by a department head before it goes to the next step.

Digitally speaking

Up to 40% of our cases come in digitally. We have two technicians that QC the scans before

distribution which has worked out fantastic. Our remake factor is below 2%. The problem is that there are a lot of doctors that don’t take it well if you tell them their information isn’t clear. I tell them that they didn’t pass our QC process, but if they insist on us proceeding with the work anyway, that we will charge them a second time if the product doesn’t fit. Many doctors don’t participate in continuing education and sometimes don’t know how to deal with a product. So we have technicians that go chairside and that also eliminates a lot of remakes.

QC the QC

We not only have our QC department but the owners and general manager spot QC every day and we also have QC meetings two days a week. On top of that we have a QC card sent with every case that offers a 10% discount on the next case if it’s filled out and returned. This opens up the lines of communication with the doctor and provides a chance to update their preferences. It’s critical to catch issues right away as a doctor might not bother communicating concerns and just go to another lab. You need to find the system that works for a lab of your size and be willing to adapt if it doesn’t work. We used to have all products being QC’d by one group but found that they weren’t well-versed in different areas. Now they only QC products they have been trained on. We also employ dentists that are in charge of all of the QC teams and are currently considering bringing on dental hygienists. Our profit margin is affected because we place so much labor cost into the product. While the way we do things may not be profitable, we do have less remakes and also maintain client retention which saves money. Repeat cases require good QC.

spinning wheels

Good quality control isn’t easy. What I see as the biggest obstacle for other lab owners is that they are too busy doing the lab work and hide from what’s really going on around them and consequently have no control. They believe they are doing more work but in reality are just spinning their wheels and that’s why they can’t get any larger. It’s time to take off the rose-colored glasses. Just because someone is a great technician doesn’t mean they have great business sense. I’m one of the best technicians on the lab but I don’t touch the work. I do, however, try to get everyone to be better than me. It’s our lab philosophy. * http://asq.org/learn-about-quality/history-ofquality/overview/overview.html

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QUESTIONNAIRE A Comparison of the Change in Mandibular Condyle/Fossa Relationship with the Use of Anatomic Teeth and Semi-anatomic teeth in Complete Denture Prosthesis

2

B8

Question 1: The Zhang’s and Brewka’s methods were used to evaluate the condyle/fossa relation. A) True B) False Question 2: Does the condyle/fossa relation established during jaw relation change with the posterior tooth form? A) Yes B) No Question 3: When was the first semi anatomic tooth form designed? A) 1935 B) 1927 C) 1952 Question 4: Was the Hanau formula used to calculate Bennettes’ angle? A) L=H/8+12 B) H=L/12+8 C) L=H/10+12 Question 5: What were the cusp angles on the anatomic teeth used? A) 33 degrees B) 37 degrees C) 27 degrees Question 6: How many DVTs were recorded for each patient? A) 2 B) 4 C) 6 Question 7: Vertical dimension is not a critical aspect of centric relation because the mandible can ro tate around a fixed axis A) True B) False

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Do flexible acrylic resin lingual flanges improve retention of mandibular complete dentures?

2

B8

Question 8: Which guidelines were used where complete dentures were constructed? A) Hong Kong Prosthetic Dentistry Society B) British Society for the Study of Prosthetic Dentistry C) American Prosthetic Society Question 9: Which flange area was replaced by the Flexible acrylic in one of the mandibular dentures? A) B) C) D)

Buccal Anterior Lingual None of the above

Question 10: How many upper and lower dentures were constructed for the comparison of the different acrylics? A) B) C) D)

2 Full sets 2 Uppers and 1 Lower 2 Lowers and 1 Upper 1 Full set

Question 11: What is the correct temperature of the water, that a flexible denture must be submersed in for a few minutes, before being placed in the patients mouth? A) 50 degrees B) 37 degrees C) 45 degrees D) None of the above Question 12: What measurement was the retention strength measured in? A) Kilograms B) Pounds C) Grams

Payslips Are Important! A Practical Guide To Getting Them Right

1.4 E6

Question 13: Is a formal hearing always needed to dismiss an employee. A) Yes B) No

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Question 14: Is it True or False that wrongful tax deductions from an Employer could attract penalties for Employees? A) False B) True Question 15: What percentage of your salary package is tax deductible with retirement funding? A) 30.5 B) 35 C) 27.5

Making Friends with your Sintering Oven heating elements Question 16: What are the heating elements inside your sintering oven? A) SiC B) MoSi2 Question 17: What is the other material other than MoSi2 from which elements can be made were temperatures go above 1200 degrees Celsius? A) Nickel chromium B) Metallic elements C) Silicon carbide Question 18: How many degrees hotter must the furnace be to maintain a given set point? A) 50 degrees B) 200 degrees C) 20 degrees Question 19: Surface loading is measured in Watts per square inch. A) True B) False Question 20: Can cheap MoSi2 elements cause discoloration when sintering Zirconia products? A) Yes B) No Question 21: Is it better to use one or two shank element holders? A) One B) Two

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1.6 B8


1.9

Quality Control in the Laboratory

B8

Question 22: What is Daniela Hendricksonâ&#x20AC;&#x2122;s first step in QC A) A Person must check that info put into computer system is same as lab slip B) Technician with a complete overview of process must check impressions to see if correct C) For her to check that Dr. signed Lab slip Question 23: What does she find works best to discuss work issues? A) Individual B) Staff meetings Question 24: Which model for QC does Jerry Ulaszek use for his medium size Lab? A) ANA Quality Assurance Model B) Donabedian Model C) Edward Deming Model Question 25: How many quantifiable criteria have been documented for each of his departments? A) 5 B) 3 C) 7 Question 26: A Team of how many people are in each QC team of every department in the Large Lab at CDT? A) 5 B) 3 C) 2 Question 27: Below what percentage are CDTs remakes on their digital cases? A) 15 B) 8 C) 2

8.9

B8 7.5 E6 1.4

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