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January 2019 • Vol 7 Issue 3 • Absenteeism • The Mandibular Response To Occlusal Relief Using A Flat Guidance Splint • A Functional Stress Analysis In The Maxillary Complete Denture, Influenced By The Position Of Artificial Teeth And Load Levels • Corporate Governance In A Time Of Complexity And Crisis

SADTJ

ISSN 2077-2793

The Southern African Dental Technology Journal

13

E6 7 B8 6.3


The Dental Technology Association of South Africa 2019 Summit & AGM, 19 & 20 July 2019 Century City Conference Centre


In This Issue SADTJ Vol 7 Issue 3 December 2018

Editor

Axel Grabowski

Managing Editor Mariaan Roets

PUBLISHED BY

The Dental Technicians Association of South Africa

LAYOUT AND DESIGN Nicola van Rensburg

Absenteeism

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The Mandibular Response To Occlusal Relief Using A Flat Guidance Splint

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ADVERTISING ENQUIRIES m.roets@dentiworks.com

ADDRESS CHANGES

Elize Morris: dentasa@absamail.co.za

ACCOUNTS Elize Morris: dentasa@absamail.co.za

A Functional Stress Analysis In The Maxillary Complete Denture, Influenced By The Position Of Artificial Teeth And Load Levels

19

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

Corporate Governance In A Time Of Complexity And Crisis

Operational Management Series

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28

Beware: Employee Misreprensentation On CVs Is Getting Worse

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Using inCoris CC Sinter Metal and the inLab system

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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 official policy of the Dental Technology Association of South Africa.

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Editor’s Page Here we are once more, the year has come and gone. The highlight of 2018 was undoubtedly the DENTASA Summit and AGM. Very different. Very invigorating and exiting. A new concept that the organizing committee attempted, was a huge success. The theme, logo, T-Shirts were winners. The 2019 DENTASA Summit and AGM will be hosted by the Western Cape Branch. We wish them all the very best, and I am sure it will be awesome. As we all know, the fairest Cape has lots of family orientated activities, and this weekend can easily be turned into a mid-year break. Please be reminded that you can arrange an easy monthly payment scheme with the office to ease and spread the financial burden. The question of moving to the HPCSA is an ongoing concern, which will have to be addressed early next year in all earnest. Wishing all of you a well-deserved break. 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 3

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SADTJ Vol 7 Issue 3

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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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ATTENTION: ALL EMPLOYERS

Enjoy a stress-free labour environment BECOME A MEMBER TODAY spend your me be er.

Our main goal is to assist YOU as the employer, to comply with labour law. Laboratory Business/ Prac ce (Employer)

Become an LWO member

Compliance is not a luxury, but a necessity and holds a serious business risk for employers. Don’t waste me figuring out how to comply with labour law. Become a member and protect your business.

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SADTJ Vol 7 Issue 3

Ÿ Free labour audit with 100% compliance in mind

(upon joining)

Ÿ Free employment contracts compliant with your

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Ÿ Free labour law documenta on Ÿ Free 24/7 legal advice helpline Ÿ Assistance with: disciplinary hearings, warnings,

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ABSENTEEISM LWO Employers Organisation

Absenteeism is a common issue in the workplace with a huge impact that must be addressed effectively to ensure productivity.

What does absenteeism mean? Apart from not being at work, absenteeism also means: • Arriving late (it is still absence as long as the employee is not at work) •

Leaving early

Unauthorised breaks

Extended breaks (smoke, toilet, lunch, tea, etc.)

Feigned illness

Other unexplained absences from the workstation or from the premises.

It is the employee’s duty to commence and end duties at the times required by the employer. When employees do not follow the rules employers have the right to act. The employer’s disciplinary code stipulates the rules of the workplace. It is vital that these rules are in writing and discussed with employees. Only then can employers prove that employees are aware of the rules and the consequences when these rules are broken.

How to deal with Absenteeism There are three important steps: • Interview the offender and write down what he/she says •

The employee has to prove that the absence was justified

The employee may produce reasons, but even if a reason is valid it can still be unacceptable – apply the disciplinary code

Absence where the employee does not report for work at all, is sometimes the most difficult type of absenteeism to manage. Under such circumstances, the employee should notify the employer by any means possible. It is very seldom that there are no means whatsoever available of notifying the employer of the absence. Note however that even if the employee does notify the employer that he/she will be absent for the day, such notification does not mean that the absence is now justified or authorised. The employer has three options of how to deal with the absence depending on the circumstances: • request the employee to come to work; or •

treat the absence as authorised leave and pay the employee for the period absent; or

treat the absence as unpaid leave.

It is important to record all incidents including absenteeism and late coming in an incident book or an employee file and act according to the employer’s disciplinary code. The disciplinary code not only stipulates the rules but also the appropriate sanction. The measure taken and sanction given must always be fair for the type of misconduct and in terms of a fair procedure.

Absence after permission has been refused

Sometimes annual leave cannot be granted due to workload or any other valid and fair reason. When the employee still goes ahead to take the said leave, the employee can be charged with unauthorised absenteeism, insubordination and refusing to obey reasonable and lawful instructions. However, the employer’s disciplinary code needs to be followed. For first offenders a final written warning would be a more appropriate sanction.

Desertion

A deserter is an employee who is absent from work for more than five days, without notifying the employer of the reason for the absence. It is extremely important that the employer must be able to prove that the employee has no intention of

SADTJ Vol 7 Issue 3

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returning to work. Therefore the employer must attempt to contact the employee and have proof of these attempts – an SMS or a letter sent to the employee’s last known address will suffice. It is the employee’s duty to notify the employer of a change of address. After the initial attempts to contact the employee, disciplinary measures can be taken. The employer must send a notice of disciplinary hearing to all last known contact details of the employee. A hearing must be held and may proceed in absentia after which the employee may then be dismissed.

The disciplinary hearing

During the disciplinary hearing the employer must provide evidence attesting to the employee’s unauthorised absence, as well as the steps taken by the employer to contact the employee. The chairperson at the hearing then evaluates all evidence presented and proceeds to make a finding. When the employee is found guilty of absenteeism, the employer must notify the employee of the sanction according to the chairperson’s finding. There are various factors to consider when deciding on the appropriate sanction: •

length of absence;

reason for absence;

attempts made by the employee to contact the employer during his/her absence;

previous warnings for absenteeism;

whether there is a rule or policy requiring the employee to contact his manager/employer regarding his absence;

the employee’s position and type of work done; and

whether the employer had to replace the employee.

Clear rules and guidelines ensure that friction and misunderstandings are kept to a minimum, which promotes not only productivity, but also a positive working environment. Labour risk needs to be managed in a proactive manner.

Absenteeism Question 1 A B C D

report at least 15 minutes early for duty commence and end duties at the times required by the employer work through lunch without a break when the employee reported late for duty pay a fine for absenteeism

Question 2 A B C D

The rules of the workplace with appropriate sanctions are stipulated in the -

employer’s policies employer’s procedures employer’s disciplinary code employer’s code of good practice

Question 3 A B C D

With regards to timekeeping, it is the employee’s duty to -

What does “absenteeism” NOT mean:

flexi time unauthorized breaks arriving late, leaving early extended breaks

Question 4

It is the employee’s duty to notify the employer of any absenteeism.

A True B False

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SADTJ Vol 7 Issue 3

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E6


Question 5 A B C D

The employer has three options of how to deal with an employee’s absence depending on the circumstances, which options below are NOT true:

request the employee to come to work treat the absence as authorized leave and pay the employee for the period absent treat the absence as unpaid leave automatically deduct any damages incurred as a result thereof from the employee’s remuneration

Question 6

What is desertion?

A

Desertion is when an employee is absent from work for more than five days without notifying the employer of the reason for the absence, and without the intention of returning to work

B

Desertion is when an employee is absent from work without the intention of returning to work

C

Desertion is when an employee is absent from work for more than three days without notifying the employer of the reason for the absence, and without the intention of returning to work

D

Desertion is when an employee is absent from work for more than five days without notifying the employer of the reason for the absence

“The LWO assists employers to not only comply with labour law, but also to use it to their advantage to protect their business and rights as an employer. The LWO is a registered employers’ organisation with the Department of Labour and has the right to represent our members at the CCMA, Bargaining Councils and Labour Court. Contact the LWO at ansofie@lwo.co.za.”

SADTJ Vol 7 Issue 3

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original article J. Stomat. Occ. Med. (2013) 6:134–139 DOI 10.1007/s12548-013-0093-8

The mandibular response to occlusal relief using a flat guidance splint G. Reichardt · Y. Miyakawa · T. Otsuka · S. Sato

Received: 21 May 2013 / Accepted: 5 August 2013 / Published online: 17 September 2013 © The Author(s) 2013. This article is published with open access at Springerlink.com

Abstract Background The mechanism of action of occlusal splints used for the successful treatment of temporomandibular disorders (TMD) remains unclear and controversial. Aim The aim of this study was to observe the mandibular response during sleep bruxism (SB) on the elimination of occlusal influences by using a flat anterior and lateral guidance splint (FGS). Material and method Any changes in mandibular movement patterns and condylar position with the introduction of this tool were measured. Current SB activity on the natural dentition was evaluated using a Brux Checker® (BC) and compared with the activity after insertion of an FGS in 153 subjects. Result The spatial mandibular position changed individually with a tendency toward forward and downward movement. The insertion of an FGS led to a change in the topographical condyle-fossa relationship and seemed to create an “unloading” condition for the temporomandibular joint. It was found that increased angulation of the maxillar incisors was responsible for altered muscular activity during sleep. Conclusion The masticatory organ appears to selfregulate and to provide an oral behavior modification, which may be more physiological using the FGS as a compensating factor. In this context, it is assumed that sleep bruxism in terms of parafunctional activity is a physiological function of the masticatory organ. The

G. Reichardt, D.D.S. () · Y. Miyakawa Private Dental Office „Ihre Zahnärzte“, Landhausstrasse 74, 70190 Stuttgart, Germany e-mail: g.reichardt@landhausstrasse.com G. Reichardt, D.D.S. · T. Otsuka · S. Sato Department of Craniofacial Growth and Developmental Dentistry Kanagawa Dental University, 82 Inaoka-cho, Yokosuka, Kanagawa 238-8580, Japan

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results of this study indicate the importance of controlling anterior guidance in the functional reconstruction of human occlusion. Keywords Sleep bruxism · Tooth grinding · Brux checker  · Temporomandibular joint  · Temporomandibular disorders · Occlusal splint

Introduction Many health problems related to the masticatory organ and neighboring structures, such as temporomandibular disorders (TMD) are often associated with parafunctional activities. Oral splints are the most common therapeutic approach used to treat patients diagnosed with TMD [1] and protect the teeth from damage resulting from forceful jaw muscle contractions and reduce concomitant orofacial pain if present [2–5]. There is no consensus on the clinical indications and functioning of oral splints. With respect to the placebo effect, changes in occlusion, improvement in jaw muscle function, oral behavior modification, the recruitment of different motor units, behavioral intervention and new positioning of the condyle and/or the articular disc, the mechanism of efficacy is not fully understood [6–11]; however it is generally recognized that splints are useful in the conservative treatment of TMD [6–8, 10, 12]. Regardless of the mode of action, several randomized clinical trials and literature reviews have documented the therapeutic effectiveness of oral splints [13–16]. It is difficult to study sleep bruxism (SB) because of the difficulty in evaluating the actual oral behavior; however, the Brux Checker® (BC) which is an effective tool for diagnosing and classifying these phenomena has been on the market for several years and is available for functional analysis. It is possible to visualize occlusal patterns which are clinical signs of grinding on occlusal interferences in SB [17, 18]. Especially

134 VolThe response to occlusal relief using a flat guidance splint SADTJ 7 mandibular Issue 3


original article

SB is defined as a non-functional activity of masticatory muscles during sleep [19]. There is no evidence that current occlusal interference could be a factor in static and dynamic occlusion leading to muscular hyperactivity and structural defects. Therefore, this was targeted as the topic of this research. The aim of this study was to investigate the effect of the occlusion on oral behavior modification such as parafunction during sleep. The effect of a flat anterior and lateral guidance splint (FGS), which provides an environment free of posterior contact during mandibular translation was analyzed and the behavior of the jaw muscles in relation to changes in the spatial mandibular position that lead to new positioning of the condyles and the modification of oral behavior was evaluated.

Material and methods Subjects Between January 2009 and December 2010 a total of 153 consecutive patients (62 males and 91 females; average age, 46.6 years, range, 18–77 years) representing TMD with and without subjective symptoms, were enrolled for this study. Condylographic tracing (Cadiax, Gamma Dental, Klosterneuburg, Austria) was conducted and the individual condylar hinge axis of each patient and its casts were transferred to an articulator. For inclusion in the study the patients had to meet all of the following criteria: (1) a set of permanent teeth in the maxilla and mandible with reliable posterior support on both sides, (2) a complete set of frontal dentition

(canine to canine), (3) aged 18–80 years and in good general health. The exclusion criteria were previous experience with occlusal splint therapy, any physiotherapy within the past 6 months, the use of medication with possible effects on muscular behavior, alcohol or drug abuse and ongoing dental therapy including orthodontic treatment.

Experimental procedure and oral splint fabrication The study evaluated two oral devices. (1) A set of BCs was used for the maxilla and the mandible to observe the SB on the present dentition of the subjects (Fig. 1a). (2) An FGS covering the teeth with a flat posterior support zone was inserted on the mandibular arch; the angulation of the lateral and anterior guidance was minimal (as flat as possible) but steep enough to disocclude all premolars and molars in any dynamic mandibular activity (Fig. 1b). Maxillary and mandibular arch impressions were obtained with alginate in an individualized tray and models were cast in artificial plaster type 4 dental stone (Fujirock EP, GC, Leuven, Belgium). The centric relation, the reference position (RP) was obtained with a bite plate (light curing custom tray material, Supertec, DMG, Hamburg, Germany) and optimized adaptation to the maxillar dentition was implemented using pattern resin (acrylic resin for patterns, Pattern Resin LS, GC, Tokyo, Japan). The bite registration of the mandibular dentition (3/7) was preserved with Alu-wax (accurate bite registration wax, Alminax, Kemdent, Swindon, UK). A kinematic face bow (Condylograph, Gamma Dental)

Fig. 1 Method of data acquisition and analysis a Brux Checker® on a stone model of a patient’s maxillar dentition, b a dyed flat guidance splint on a stone model of a patient’s mandibular dentition, c spatial mandibular positions and d occlusal guidance measurement

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original article

was used to mount the models in an adjustable articulator (Reference SL, Gamma Dental) with a standardized verticalization of 7 mm on the incisal pin. The BCs (analytic foil 0.1 × 125 mm, Brux Checker®, Scheu Dental Technology, Iserlohn, Germany) were based on the two models and each was used for two nights separately in the maxilla and mandible according to previous reports [17]. The FGS (cold curing denture base material, Pro Base Cold, Ivoclar, Schaan, Liechtenstein) was fabricated using a wax-up method and pressed on the mandibular model. It was inserted and adjusted in the patient’s mouth without any manual guidance by the operator while the patient was placed in a sitting position in a dental chair. Uniform occlusal contacts were created to hold the Shimstock foil (Shimstock foil 8 μ, Hanel, Langenau, Germany) on the lingual cusps of the molars and the premolars against the splint to provide reliable static stability. The anterior teeth and the cuspids were lightly touching the splint but not holding the Shimstock foil. Lateral movements were guided by the tips of the maxillar canines; protrusive movements were guided by the incisal edges of the maxillar front teeth against a horizontal anterior ramp of the FGS. In any excursion, dynamic interference in the molars and the premolars was eliminated. The same operator (GR) provided the treatment and each patient was given the same instructions. The patients were asked to wear the splint continuously for 24 h except when eating and when cleaning the teeth. After 7 days in the following session, the splint was adjusted using the described adjustment procedure. To obtain reproducible stability for the FGS with no change from one weekly appointment to the next 2–5 sessions were necessary.

Recording the static mandibular position and dynamic activity during sleep To visualize the muscular reaction and static stability of the mandible and the dynamic activity on the FGS the color indicator effect of red dye (Acid red 51, Morimoto Chemical, Tokyo, Japan) was used. Subjects wore the red dye treated splint for two consecutive nights. The following morning digital photographs (digital camera, D90, Nikon, Tokyo, Japan; dental lens system, DCN16-LV/GP2, Sonic Techno, Tokyo, Japan) of the result were obtained and four Alu-wax stops (3, 3 and 7, 7) were placed on the splint. The splint was reinserted in the subject’s mouth and the mouth was closed normally. The acquired and conserved mandibular position, which was labeled as the occlusion relieved position (ORP), was retransferred to the articulator using the splint with the four Alu-wax stops and the original casts. To evaluate the effect of an FGS, three reliable spatial mandibular positions were compared (Fig. 1c):

Comparative measurements of the patient casts were performed using the Condylar Position Measurement (CPM SL, Gamma Dental). Each spatial mandibular change was accurately measured with a magnifying glass (# 2004 Scale Loupe 10x, PEAK, Tokyo, Japan).

Classification of the result between Brux Checker® and flat guidance splint The major axis of the wear facets of the canines and central incisor found on BC and FGS was measured using a magnifying glass and the values were mapped in relationship to one another. A matching type group to a coincidence less than 30 % was defined. Higher values were defined as changing type group.

Measurement of occlusal guidance To investigate the influence of occlusion on parafunctional activities, the occlusal guiding surfaces to the AOP in the maxilla were measured according to previous reports [20] (3d- Digitizer, Gamma Dental) (Fig. 1d).

Statistical analysis A Wilcoxon signed rank test was used to compare the spatial distance obtained from RP-ICP with the RP-ORP provided by the FGS. The significance level was set at p < 0.05. Student’s paired t-test was used to compare the mean angle of each tooth between the matching type and the changing type. The significance level was set at p < 0.05.

Results Reactive adaptation of the condylar position The ORP had a large standard deviation. The average tendency was downward and forward compared with the RP and the ICP (Fig. 2).

Classification of grinding pattern on the dentition (Brux Checker analysis) After wearing the BC for two consecutive nights, the grinding pattern of the subjects had transferred to the surface of the BC and was observed by the removal of the painted areas, which were removed by clenching and grinding. The wear site and pattern were then evaluated. The BC presented different characters in SB that were classified into seven groups (Fig. 3a).

1. Reference position (RP) 2. Intercuspal position (ICP) 3. Occlusion relieved position (ORP)

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original article Classification of the grinding pattern on the flat guidance splint The FGS results were classified into five types in a manner similar to the BC (Fig. 3b).

Characteristic of sleep bruxism behavior on dentition and flat guidance splint Comparing the SB behavior on the dentition with the use of an FGS, a change in the character of the behavior was observed in many subjects. One group showed the same direction of mandibular movement for both conditions (matching type). The other group showed a different activity (changing type) and these groups were distributed 94:59 (Fig. 4a).

Influence of occlusal guidance on oral behavior

Fig. 2 The changes in spatial condylar relationships. a The average sagittal condylar change of ICP and ORP compared to RP (=0) and b the mean SD of the spatial change of ICP and ORP compared to RP in the x and z direction. No significance is shown by Δy

The occlusal guidance of all maxillae was measured to investigate its influence on parafunctional activity. The result of the BC reflects the behavior in present dentition. The mandibular incisors and cuspids glide along the surfaces of their maxillar counterparts and create individual wear facets. Using an FGS, any posterior contact during mandibular translation was eliminated; the effect of the anterior “flat” ramp provided an immediate anterior and lateral guidance, less accentuated as individually pos-

Fig. 3 The classification of grinding activities in sleep bruxism and their distribution. a The grinding pattern distribution in natural dentition observed using a bruxchecker and b the distribution of occlusion relieved and muscle-dictated grinding found after application of the flat guidance splint. The white sites indicate the bruxism activity The mandibular response to occlusal relief using a flat guidance splint

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original article

Fig. 4 Examples of the mandibular response to occlusal relief using a flat guidance splint and the corresponding statistical distribution. a Clinical examples of the matching and the changing types and b the influence of steep anterior guidance in the maxillar dentition

sible because only the tips of the maxillar incisors and canines slightly touched it. By this means a pure canine guidance was installed which was kept as shallow as possible. The predominant factor in the changing group was the increasing angle of the central (p < 0.001) and lateral incisors (p < 0.01) of the maxilla. The canines also demonstrated a significant difference (p < 0.05). For the other teeth, the difference in angulation between the two types was not significant.

Discussion The objective of this study was to analyze the effect of an FGS on oral behavior modification such as parafunction during sleep. This study is probably the first to analyze the changes in muscle behavior caused by occlusion relief, the elimination of present occlusion as an influencing factor for the neuromuscular system. A previous study with young healthy subjects showed that an increase in the steepness of occlusal guidance leads to a modification of masticatory muscle behavior and condylar position [21] and may contribute to the development of TMD symptoms. These results were supported by modern functional magnetic resonance imaging (fMRI) studies. It was demonstrated that a steepened frontal guidance creates a retral forced bite that leads to a compressive condition in the TMJ accompanied by increased activ-

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ity in the stress- assimilating areas of the brain [22, 23]. In this study the opposite approach was used to show how muscles can be influenced by anterior and lateral guidance. Because an FGS eliminates all occlusal interferences that may disturb harmonic mandibular function, the end results of the study show a spatial change in the condylar position, which varied among individuals. However, it is arguable whether the difference in condylar position translates into joint load reduction. The data indicate a slight ventral and caudal shift of the condyle in subjects wearing an FGS. However, the high reproducibility of ORP may indicate that the masticatory organ experiences some sort of muscular self-regulation. These results should be supported by controlled fMRI studies that investigate brain activity and could be the focus of further studies. Using the BC technique the actual SB activity of each subject was investigated. The results are consistent with the results of previous studies suggesting the existence of a classifiable effect of grinding on the dentition due to SB [16, 17]. In this sample a pure clenching group was additionally observed and added to the previous classifications. The effect of occlusion relief using the FGS was investigated and the results indicate different but classifiable grinding patterns that could be divided into five groups. By comparing the wear sites (paint removal caused by SB) as well on the BC as on the FGS, many subjects showed changes in quantity and direction. It can be assumed that these changes of parafunctional activity are due to a modification of the neuromuscular system. One group demonstrated coincidence of mandibular movement under both conditions (matching type); the other group demonstrated a different characteristic (changing type) and a ratio of 3:2 was observed for the number of subjects in the groups. To determine the trigger for the change in behavior after occlusion relief, the occlusal guidance of the maxilla was measured to investigate its influence on SB activity. The predominant factor in the changing group was the increased angulation of the maxillar incisors and the cuspids. Other teeth showed no significant influence on muscle behavior. As described earlier steep guidance in the maxillar front teeth may indicate a risk for occlusal trauma [24]; however, the observation of a change in the muscle behavior following splint therapy must be interpreted with caution. The findings of the condition with occlusion relief were taken from an artificial occlusion generated by a splint. Although this technique is currently the conventional method to treat TMD patients, it must be noted that the real effect of splint therapy is still unknown and highly controversial. In conclusion, the mandibular response to occlusal relief using an FGS presented a reliable and stable spatial mandibular position. Occlusion seems to affect muscle activity and oral behavior. Additionally, the steepness of the anterior guidance, particularly the inclination of the incisors, appears to significantly influence muscle activity during sleep. The results of this study support the interest to control anterior and lateral guidance in the functional reconstruction of human occlusion.

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original article Acknowledgments This study was performed in the private dental office “Ihre Zahnärzte Landhausstrasse 74” in Stuttgart, Germany, in association with the Kanagawa Dental University Research Institute of Occlusion Medicine, Yokosuka, Kanagawa, Japan. We thank Dr. Christina Rijpstra and Dr. Alain Landry for their encouragement and expert guidance. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article. Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

References 1. Glass EG, Glaros AG, MacGlynn FD. Myofacial dysfunction: treatments used by ADA members. Cranio. 1993;11:25–9. 2. Ramfjord SP, Ash MM. Reflections on the Michigan occlusal splint. J Oral Rehabil. 1994;21:491–500. 3. Pierce CJ, Chrisman K, Bennett ME, Close JM. Stress, anticipatory stress, and psychologic measures related to sleep bruxism. J Orofac Pain. 1995;9:51–6. 4. Mehta NR, Forgione AG, Maloney G, Greene R. Different effects of nocturnal parafunction on the masticatory system: the weak link theory. Cranio. 2000;18:280–6. 5. Okeson JP. Management of temporomandibular disorders and occlusion. 5th ed. St. Louis:Mosby; 2003. 6. Dao TT, Lavigne GJ. Oral splints: the crutches for temporomandibular disorders and bruxism? Crit Rev Oral Biol Med. 1998;9:345–61. 7. Al-Ani MZ, Davies SJ, Gray RJ, Sloan P, Glenny AM. Stabilisation splint therapy for temporomandibular pain dysfunction syndrome. Cochrane Database Syst Rev. 2004;CD002778; UI:14973990. 8. Forssell H, Kalso E. Application of principles of evidencebased medicine to occlusal treatment for temporomandibular disorders: are there lessons to be learned? J Orofac Pain. 2004;18:9–22. 9. Nilner M. Does splint therapy work for temporomandibular pain? Evid Based Dent. 2004;5:65–6. 10. Turp JC, Komine F, Hugger A. Efficacy of stabilization splints for the management of patients with masticatory muscle pain: a qualitative systematic review. Clin Oral Investig. 2004;8:179–95.

11. Schindler HJ, Rues S, Turp JC, Lenz J. Heterogeneous activation of the medial pterygoid muscle during simulated clenching. Arch Oral Biol. 2006;51:498–504. 12. Glaros AG, Owais Z, Lausten L. Reduction in parafunctional activity: a potential mechanism for the effectiveness of splint therapy. J Oral Rehabil. 2007;34:97–104. 13. Kreiner M, Betancor E, Clark GT. Occlusal stabilization appliances. Evidence of their efficacy. J Am Dent Assoc. 2001;132:770–7. 14. Ekberg E, Vallon D, Nilner M. Treatment outcome of headache after occlusal appliance therapy in a randomised controlled trial among patients with temporomandibular disorders of mainly arthrogenous origin. Swed Dent J. 2002;26:115–24. 15. Kuttila M, le Bont Y, Savolainen-Niemi E, Kuttila S, Alanen P. Efficiency of occlusal appliance therapy in secondary otalgia and temporomandibular disorders. Acta Odontol Scand. 2002;60:248–54. 16. Fricton J, Look JO, Wright E, Alencar FG Jr, Chen H, Lang M, Ouyang W, Velly AM. Systematic review and meta-analysis of randomized controlled trials evaluating intraoral orthopedic appliances for temporomandibular disorders. J Orofac Pain. 2010;24(3);237–54. Review. 17. Onodera K, Kawagoe T, Sasaguri K, Protacio-Quismundo C, Sato S. The use of a Brux Checker in the evaluation of different grinding patterns during sleep bruxism. Cranio. 2006;24:292–9. 18. Tokiwa O, Park BK, Takezawa Y, Takahashi Y, Sasaguri K, Sato S. Relationship of tooth grinding pattern during sleep bruxism and dental status. Cranio. 2008;26(4):287–93. 19. Sato S, Slavicek R. The masticatory organ and stress management. Int J Stomatol Occl Med. 2008;1:51–7. 20. Slavicek R. Die funktionellen Determinanten des Kauorgans. Habilitationsschrift aus der Universitätsklinik für Zahn-, Mund- und Kieferheilkunde, Wien. 1984. pp. 9–34. 21. Tamaki K, Hori N, Fujiwara M, Yoshino T, Toyoda M, Sato S. A pilot study on masticatory muscle activities during grinding movements in occlusion with different guiding areas on working side. Bull Kanagawa Dent Coll. 2001;29:26–7. 22. Otsuka T, Watanabe K, Hirano Y, Kubo K, Miyake S, Sato S, Sasaguri K. Effects of mandibular deviation on brain activation during clenching: an fMRI preliminary study. Cranio. 2009;27:88–93. 23. Greven M, Otsuka T, Zutz L, Weber B, Elger C, Sato S. The amount of TMJ Displacement correlates with brain activity. Cranio. 2011;29(4):291–6. 24. Slavicek R. Die klinische Funktionsdiagnostik und die instrumentelle Funktionsanalyse. In: Das Kauorgan: Funktionen und Dysfunktionen. Gamma Medizinischwissenschaftliche Fortbildung (ISBN 3-9501261-0-4), 2000. pp. 306–469.

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The Mandibular Response To Occlusal Relief Using A Flat Guidance Splint Question 7 A B C D

What does FGS stand for?

Flat Guidance Stent Frequently Grinding Stop Flat anterior lateral Guidance Splint Frustration and anxiety Governing System

Question 9 A B C D

Occlusal splints are used to treat what?

Crowding of teeth Temporomandibular disorder Replacement of teeth Implant placement guidance

Question 8 A B C D

2

B8

What is NOT the function of an oral splint?

To treat patients diagnosed with TMD Protect the Teeth from damage resulting from forceful jaw muscle contractions To stop teeth from drifting Reduce concomitant orofacial pain if present

Question 10 With the insertion of the FGS there was no “unloading” condition for the Tem poromandibular joint A True B False Question 11 A B C D

18

What, according to the article, was found to be of importance in the functional reconstruction of human occlusion with a FGS?

Patient’s gender Time of year Patient’s diet Controlling anterior guidance

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J Indian Prosthodont Soc (Oct-Dec 2010) 10(4):219–225 DOI 10.1007/s13191-011-0046-0

ORIGINAL ARTICLE

A Functional Stress Analysis in the Maxillary Complete Denture Influenced by the Position of Artificial Teeth and Load Levels: an In-vitro Study Naik Ravi • D. P. Krishna • Shetty Manoj Hegde Chethan

Received: 1 January 2011 / Accepted: 31 January 2011 / Published online: 10 February 2011  Indian Prosthodontic Society 2011

Abstract The fracture of complete dentures fabricated using Polymethyl methacrylate resin constitutes a challenge to the clinician and remains an unresolved problem. To determine whether gradual increase in load or different posterior teeth positions in maxillary denture would influence the pattern of stress. Two groups of maxillary dentures were fabricated with different posterior teeth positions (Group I with teeth on the crest of the ridge; Group II with buccal to the crest of the ridge.) using casts prepared from prefabricated edentulous molds, with 5 dentures in each group. Two strain gauges were cemented on to the midline of each denture, one on the anterior palatal area and other on the posterior palatal area. The dentures were loaded from 0 to 110 N in steps of 10 N, and the strains induced were measured. Differences of the stress magnitudes between the 2 groups were statistically analyzed using Mann–Whitney U test. The anterior palatal area of the maxillary denture was dominated by a tensile stress, which was greater in the group II than in group I.

Key Messages The anterior palatal area showed higher tensile stresses than in the posterior palatal area. Therefore any effort to reinforce the maxillary denture should be concentrated on the anterior palatal area. The buccal placement of the posterior teeth resulted in higher stresses in the anterior palate, therefore the placement of the posterior teeth in maxillary complete denture should be as much on the on the crest of the ridge as possible as functionally and esthetically permits. N. Ravi (&) Department of Prosthodontics, Purvanchal Institute of Dental Sciences, AL-4, Sector-7, Gida, Gorakhpur, Uttar Pradesh, India e-mail: drravinaik@yahoo.co.in D. P. Krishna  S. Manoj  H. Chethan Department of Prosthodontics, A.B. Shetty Memorial Institute of Dental Sciences, Mangalore, Karnataka, India

The posterior palatal area was dominated by compressive stress but the outer placement of the maxillary teeth caused a significant decrease in the compressive stress. The high anterior tensile stress with compressive stress in the posterior palatal area during loading may be responsible for denture base fractures that initiate from the anterior palatal area. The buccal placement of posterior teeth may play a role in the fatigue fracture of the maxillary denture. Keywords Strain gauges  Functional stress analysis  Digital strain indicator

Introduction The loss of teeth is a matter of great concern and their replacement by artificial substitute like complete denture prosthesis is vital to the continuance of normal life for esthetic and functional requirements. The complete denture prosthesis is generally fabricated using polymethyl methacrylate resin and this has a tendency to fracture under cyclic loading [1]. Complete maxillary dentures are subjected to significant variations in stress during function intra orally. The stress patterns within complete maxillary denture differs in each patient and depends on many factors like base thickness, material used, muscular power of the test subject, nature of the underlying soft tissues, stability of denture base, form and position of teeth. Complete dentures typically fracture along the midline due to crack initiation and propagation from stressed areas. Many methods of experimental stress analysis such as Brittle Coatings, Strain Gauges, Photoelastic Models, Holography, Scanning Electron Microscope Replica Technique and simulations such as Finite Element Analysis

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[2] have been used to examine the deformation of complete maxillary dentures. Clinical experience has revealed a paradox in complete maxillary dentures. Although load acts on the posterior area of the denture, fracture often begins from the anterior area where no teeth are in contact [3]. Moreover, crack propagation does not always result in separation of its direction away from the midline. The purpose of this study was to characterize the midline stress field in complete maxillary denture in terms of type and magnitude and to determine whether gradual increase in load or different posterior teeth positions would influence the pattern of stress.

Subjects and Methods A comparative in vitro study to evaluate functional stresses in maxillary complete dentures with two different posterior teeth positions at a gradual increase in load was undertaken.

J Indian Prosthodont Soc (Oct-Dec 2010) 10(4):219â&#x20AC;&#x201C;225

were transferred onto the trial acrylic bases to indicate the crest of the ridges. Then the maxillary and mandibular casts with occlusal rims were mounted on a semi adjustable articulator (Girbach Artex) in a class I anterior posterior relation. Care was taken to arrange the maxillary posterior teeth in wax so that central grooves of their occlusal surfaces coincided with the two lines transferred from the prototype maxillary cast (Fig. 2). In the same centric occlusion mandibular posterior teeth were arranged with their buccal cusps occluding to the central fossa of the maxillary posterior teeth (Fig. 3). The prototype denture of Group II was produced by changing the teeth position such that lingual cusps of the maxillary posterior teeth coincided with the guide lines on the maxillary cast (Fig. 4). In the same centric occlusion mandibular posterior teeth were arranged with their buccal cusps occluding to the central fossa of the maxillary posterior teeth (Fig. 5).

Fabrication of Prototype Denture Two prefabricated edentulous molds (Edentulous mold No 402) one of the maxillary jaw and one of the mandibular jaw were selected for the fabrication of the prototype complete dentures for each group. Edentulous casts of maxillary and mandibular jaw were made in the molds using Dental stone type III (Kalastone cl III, kalabhai, Mumbai). For group I two guidelines were drawn on prototype maxillary cast to coincide with the longitudinal axis of the ridge crest (Fig. 1). A 2.5 mm thick thermoplastic sheet (ERKOPRESS) was vacuum pressed on the maxillary cast to obtain trial acrylic base of uniform thickness. The lines Fig. 2 Group I prototype denture with teeth on the crest of the ridge

Fig. 1 Guide lines on the maxillary cast

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Fig. 3 Waxed up denture for group I


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Fig. 7 Group I denture specimens

Fig. 4 Group II prototype denture with teeth buccal to the crest of the ridge

Fig. 8 Group II denture specimens

Processing of Denture Specimens

Fig. 5 Waxed up denture for group II

The waxed dentures are cured with heat cure denture base material (DPI Mumbai) using standard curing cycles according to manufacturerâ&#x20AC;&#x2122;s recommendations (Figs. 7, 8). Functional Stress Analysis of Denture Specimens

Fig. 6 Silicone duplicating material with duplicating flask and acrylic teeth

Duplication of the Prototype Denture Five identical dentures were produced for each of the two groups by duplicating the prototype denture with silicone duplicating material (Wirosil: Bego, Germany) in duplicating flask (Combi Duplicating Flask; Bego, Germany) (Fig. 6).

Two strain gauges (foil type 350 X; Industrial Engineering Equipments, Bangalore India) were cemented onto each denture specimen with cyanoacrylate cement (EP-160; Industrial Engineering Equipments) (Fig. 9). One of the strain gauge was cemented on to the mid-line of the intaglio surface of the denture 6 mm from the contact point of central incisors. The other strain gauge was cemented onto the mid-line of the same surface 4 mm from the posterior border of the denture [4]. Two identical strain gauges were also cemented on an acrylic plate made from the same material with the same procedures as for the complete denture specimens. These gauges were used as references (dummy gauges) in Wheatstone bridge circuit. Each of the denture strain gauge was an active gauge and was connected to each element of the plate strain gauge that formed the dummy gauge of the same half-bridge circuit. This arrangement resulted in 2 pairs of strain gauges connected to a 2-position digital strain-gauge indicator (2-channel strain indicator; Industrial Engineering Equipments, Bangalore India).

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The dentures were loaded from 0 to 110 N in steps of 10 N. The associated strains were measured at each strain gauge, which were then substituted into the standard equations to calculate the principle stresses at every load level. Modulus of elasticity for heat cure denture base resin (PMMA) is 2350 MPa.

Results

Fig. 9 Maxillary denture with strain gauges

Each maxillary and the mandibular denture specimens were mounted on the die stone casts produced by high strength type IV dental stone (Kalrock, die stone class IV, Kalabhai Karson Pvt. Ltd. India). Before the denture specimens were placed on the load casts, their inner surfaces were painted with mediumâ&#x20AC;&#x201C;viscosity silicone (Coltex Medium, Coltene) to simulate the oral mucosa. According to in vivo measurements, the thickness of the masticatory mucosa ranges from 1.92 to 2.38 mm at the maxillary edentulous ridge and from 1.45 to 1.58 mm at the mandibular edentulous ridge [5]. Therefore, to ensure that the thickness of the masticatory mucosa in vivo, 2 and 1.5 mm thickness of die stone were removed from the residual ridges of the maxillary cast and Mandibular cast, respectively, before the placement of painted specimens (Fig. 10). The maxillary and mandibular dentures were positioned in the centric occlusion, and their mounted casts were placed between the plates of a loading instrument (Fig. 11).

Fig. 10 Silicone lined maxillary and mandibular casts

123

Stresses were calculated at anterior and posterior palate in the midline for each denture specimen in both the groups. A Mannâ&#x20AC;&#x201C;Whitney U test was used to evaluate the statistical significance of the differences in the stress magnitudes between the two groups. The anterior palatal area of the maxillary denture was dominated by a principal tensile stress, irrespective of the posterior teeth positions and load levels but the tensile stress of the anterior palate was greater in the group II (?6.88 MPa at 110 N load) than in group I (?2.99 MPa at 110 N load). The posterior palatal area was dominated by compressive stresses but the outer placement of the maxillary teeth caused a significant decrease in the compressive stresses in group II.

Discussion The fracture of complete dentures is an unresolved problem in Removable Prosthodontics despite numerous attempts to determine its causes. Despite the high frequency of denture fracture, there is surprisingly little discussion of the subject in the literature. Complete maxillary dentures are subjected to significant variation in stress during function intra orally. The stress patterns within maxillary complete denture differs in each patient and depends on many factors like base thickness, material used, muscular power of the test object, nature of the underlying soft tissues, stability of the denture base, form and position of teeth. These stress patterns also influence the flexural fatigue in the denture. Maxillary denture bases deform during functional and para functional activities such as chewing, biting, swallowing and clenching. It deforms in a direction away from the palatal tissues causing internal stresses. Therefore, fatigue stress is a significant factor in fracture. Detailed photo stress analysis indicated that compressive stresses occurred toward the tissue surface, with greater values beneath the teeth and on the ridge than those toward the palate [6]. Many techniques have been used to examine the stresses and strains in a complete maxillary denture like Brittle coatings, Strain gauges, Photoelastic models, Holography


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223

Fig. 11 Digital strain gauge indicator and loading instrument

scanning electron microscopy replica technique, and simulations such as finite element analysis. The use of stain gauges represents a simple and accurate method for measuring stresses developed for plane state of stress or surface stresses. The application of strain gauges in vitro can provide data that are more useful than data from in vivo measurement, as the inadequate sealing of the gauges may produce short circuits that could introduce measurement errors [7, 8]. Sharry [9] proposed in his palatographic study that a thin well-adapted denture base (about 1.5 mm) does not significantly impair speech. However, raising the denture base thickness (to about 2.5 mm) showed marked deficiency in speech clarity and comfort. On the other hand, Farmer [10] stated that denture bases less than 2 mm in thickness were more prone to fracture. Using this aforementioned information, in the present study it was decided to standardize the denture base thickness for all the denture specimens at 2 mm using a 2 mm thick thermoplastic sheet which was vacuum pressed on the maxillary cast to obtain trial acrylic base of uniform thickness. Gibbs et al. [11] showed that the average closing force during mastication of complete denture wearers is only 11.7 lb, which is considerably below the weakest closing force of subjects with natural teeth. Prombonas and Vlissidis [12] showed that the force exerted by the edentulous patients at the vertical dimensional of occlusion ranges from 30 to 110 N. Using this aforementioned information, in the present study it was decided to use an optimum load of 0 to 110 N to analyze the functional stress in the maxillary complete denture. In the present study the stress patterns in the anterior palatal area of all denture specimens were predominantly tensile in nature, irrespective of position of the teeth in relation to the crest of the ridge and load levels. The magnitude of tensile stress increased as the load increased from 0 to 110 N in both the groups. The tensile stress of the anterior palate was greater in the group II with outer placement of maxillary posterior teeth (mean maximum stress of 6.88 Mpa at 110 N) (Table 1) than in group I with teeth on the crest of the ridge (mean maximum stress

Table 1 Calculated mean stress magnitudes of anterior palatal area for group I and group II Load (N)

n

Mean (MPa)

Mean (MPa)

10

5

?0.2060

?0.5580

20

5

?0.6380

?1.1760

30

5

?1.1340

?2.0120

40

5

?1.4440

?2.9200

50

5

?1.7120

?3.6800

60

5

?1.9300

?4.2720

70 80

5 5

?2.1380 ?2.3140

?4.7860 ?5.3420

90

5

?2.5620

?5.9920

100

5

?2.7920

?6.5320

110

5

?2.9940

?6.8880

Positive values indicates tensile stress N Newtons; n number of specimens; MPa mega pascal Table 2 Calculated mean stress magnitudes of posterior palatal area for group I and group II Load(n)

n

Mean (MPa)

Mean (MPa)

10

5

-0.1520

-0.2360

20 30

5 5

-0.6580 -1.2720

-0.4640 -0.7300

40

5

-1.6720

-0.9200

50

5

-2.0620

-1.1000

60

5

-2.4440

-1.2700

70

5

-2.8120

-1.4840

80

5

-3.1720

-1.6520

90

5

-3.4780

-1.7680

100

5

-3.7180

-1.9680

110

5

-4.0000

-2.2260

Negative values indicates compressive stress

of 2.99 Mpa at 110 N) (Table 1), and difference was statistically significant (P \ 0.05) (Table 3). The patterns of stresses in the posterior palate in all denture specimens in both the groups were predominantly compressive in nature. The outer placement of the posterior teeth resulted in an unexpected decrease in the compressive

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Table 3 Shows statistical comparison of stress magnitudes of anterior and posterior palatal area between group I and II Load (N)

n

Z1

P1

Z2

P2

10

5

-2.643

0.008 hs

-1.576

0.115 ns

20

5

-2.611

0.009 hs

-1.362

0.0173 ns

30

5

-2.611

0.009 hs

-2.095

0.036 sig

40

5

-2.611

0.009 hs

-2.193

0.028 sig

50

5

-2.619

0.009 hs

-2.402

0.016 sig

60

5

-2.619

0.009 hs

-2.611

0.009 hs

70

5

-2.611

0.009 hs

-2.611

0.009 hs

80

5

-2.611

0.009 hs

-2.611

0.009 hs

90

5

-2.619

0.009 hs

-2.611

0.009 hs

100

5

-2.611

0.009 hs

-2.611

0.009 hs

110

5

-2.610

0.009 hs

-2.610

0.009 hs

complete maxillary denture. They concluded that the buccal placement of occlusal contacts may play a role in fatigue fracture of the complete maxillary denture. The results of the present study agree with those of Stafford and Griffiths [14] who used a rosette strain gauge to measure the principal stresses in the posterior palatal area of a complete maxillary denture. They measured principal stresses that ranged from 0.001 to 3.97 MPa.

Conclusions Within the limitations of this study, the following conclusions were drawn: 1.

Z Mann–Whitney U Test, hs highly significant, sig significant, P probability, ns no significance

stresses in the group II (maximum stress of 2.22 Mpa at 110 N) (Table 2) when compared to group I (maximum stress of 4.00 Mpa at 110 N) (Table 2) and the difference was statistically significant (P \ 0.05) (Table 3). By reviewing the results of this study, critical questions concerning complete maxillary denture fractures may now be answered. When the posterior teeth are set over the buccal slope of the ridge, there is rotation of the denture base around the crest of the ridge which causes increased tensile stress in the anterior palatal area. The maximum tensile stress in the anterior palatal area was always perpendicular to the mid-line, irrespective of the teeth position or load levels. Because of the brittle nature of denture base materials (PMMA) which are much stronger in compression than in tension the cracks always, begin in anterior palatal area which showed high tensile stresses. In contrast to the anterior palatal area, the pattern of stresses in the posterior palatal area of the complete maxillary denture exhibited a high compressive stress. The compressive nature of the posterior palatal area, as exhibited in this study, may explain why the crack never started from the posterior palatal area. However, in situations in which the crack crossed the posterior palatal area and met a compressive stress lower than the tensile stress that was perpendicular to the mid line, the denture base fractured into two pieces. By reviewing the results of this study it can be stated that the buccal placement of posterior teeth in relation to crest of the ridge may play a significant role in the fatigue fracture of the complete maxillary denture. The results of the present study agree with those of Ates et al. [13] who stated that shifting the occlusal contacts to a more buccal localization resulted in an increase of the calculated stresses towards midline (tensile) of the palate in

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2.

3.

The outer placement of the posterior teeth in Group II resulted in increased principal stresses (tensile) of the anterior palatal area and an unexpected decrease of the principal stresses in the posterior palatal area. The combined pattern of the stress fields in anterior and posterior palatal area may be the main reason that fractures start from the anterior palatal area and may stop or change direction during propagation to the posterior area due to compressive nature of the stresses in this area. The buccal placement of posterior teeth in relation to crest of the ridge may play a role in the fatigue fracture of the complete maxillary denture.

Conflict of interest

None.

References 1. Prombonas AE, Vlissidis DS (2006) Comparison of the midline stress fields in maxillary and mandibular dentures: a pilot study. J Prosthet Dent 95:63–70 2. Rees JS, Hugget R, Harrison A (1990) Finite element analysis of the stress concentrating effect of frenal notches in complete dentures. Int J Prosthodont 3:238–240 3. Valittu PK (1996) Fracture surface characteristics of damaged acrylic resin based dentures as analyzed by SEM-replica technique. J Oral Rehabil 23:524–529 4. Prombonas AE, Vlissidis DS (2002) Effects of the position of artificial teeth and load levels on stress in the complete maxillary denture. J Prosthet Dent 88:415–422 5. Uchida H, Kobayashi K, Nagao M (1989) Measurement in vivo masticatory thickness with 20 MHz B-mode ultrasonic diagnostic equipment. J Dent Rec 68:95–100 6. Klotzer VW (1964) Spannungsoptiche Festigkeitsuntersuchungen einiger Prosthesentypen. Dtsch Zahnaertztl Z 19:375 7. Darbar UR, Huggett R, Harrison A (1994) Stress analysis techniques in complete dentures. J Dent 22:259–264 8. El-Ghazali S, Nilner K, Wallenius K (1991) The functional deformation of maxillary complete denture in patients with flabby ridges. Part II after surgery. Swed Dent J 15:63–70 9. Sharry JJ (1974) Complete denture prosthodontics, 3rd edn. Blakiston Division, McGraw Hill Inc., New York, USA, p 139


J Indian Prosthodont Soc (Oct-Dec 2010) 10:219–225 10. Farmer JB (1983) Preventive prosthodontics: maxillary dental fracture. J Prosthet Dent 50(2):172–175 11. Gibbs CH, Mahan PE, Lundeen HC (1981) Occlusal forces during chewing-influences of biting strength and food consistency. J Prosthet Dent 46:561–567 12. Prombonas A, Vlissidis D, Molyvdas P (1994) The effect of altering the vertical dimension of occlusion on biting force. J Prosthet Dent 71:139–143

225 13. Ates M, Cilingir A, Sulun T, Sunbuloglu E, Bozdag E (2006) The effect of occlusal contact localization on the stress distribution in complete maxillary denture. J Oral Rehabil 33:509–513 14. Stafford GD, Griffiths DW (1979) Investigation of the strain produced in maxillary complete denture in fuction. J Oral Rehabil 6:241–256

A Functional Stress Analysis In The Maxillary Complete Denture, Influenced By The Position Of Artificial Teeth And Load Levels

1.9 B8

Question 12: Stress patterns in complete maxillary dentures may depend on many factors, such as: a) b) c) d) e)

base thickness muscular power of the patient position of the teeth none of the above all of the above

Question 13: What material was used to simulate oral mucosa in the stress testing exercise? a) b) c) d) e)

dental stone pink denture wax medium viscosity silicone alginate impression material silicone duplicating material

Question 14: What may cause a maxillary denture base to deform? a) b) c) d) e)

chewing biting swallowing clenching all of the above

Question 15: In this study detailed photo stress analysis indicated that compressive stresses occurred toward the tissue surface, with greater values .... a) b) c) d) e)

beneath the teeth on the ridge toward the palate a) and b) b) and c)

Question 16: What thickness denture base did Sharry propose would not significantly affect speech? a) b) c) d) e)

1mm 1.5mm 2mm 2.5mm 3mm

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CORPORATE GOVERNANCE IN A TIME OF COMPLEXITY AND CRISIS Events have moved swiftly in recent years. One of the largest South African conglomerates, Steinhoff, has virtually collapsed amidst allegations of dubious structures and transactions. Some of our largest state companies have it seems been ravaged by state capture whilst global icons such as KPMG and McKinsey have suffered serious reputational damage. A failure of governance links these entities together and there has been renewed interest in business ensuring that their organisations are well governed. WHAT TO DO TO ACHIEVE COMPLIANCE It’s not a question of poor governance being practiced by the business community as a whole – the vast majority want to do the right thing and make every effort to achieve compliance throughout their organisations. There is no surprise therefore that there has been resurgence in interest in the King IV Report on Corporate Governance. King IV applies to all businesses and is a statement of principles based on strong ethical leadership which results in: •

An ethical culture

• Legitimacy •

Successful trading

Control over the organisation.

SHAREHOLDERS VERSUS STAKEHOLDERS One of the frequent criticisms of the free market system is the primacy of shareholder interests. These interests are often prioritised at the expense of other stakeholders as shareholders want to see the maximisation of profit. King IV talks of adopting an inclusive stakeholder approach in which business creates value for society. It recognises that business and the community are, in the long term, intertwined. Being a good corporate citizen is not just good for business but is a key part of obtaining legitimacy. HOW EASY IS IT TO BE COMPLIANT IN SOUTH AFRICA? A Compliance Complexity Index was recently compiled to see how easy or difficult it is for countries to achieve compliance – 84 countries were surveyed. South Africa came in the last quartile. Generally, countries where corporate law is based on the common law fared the best. Thus, Ireland is rated the easiest country for compliance and countries where more complex laws are incorporated in their legal systems fared worst. The onus is on our authorities to simplify compliance for its citizens and businesses.

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Corporate Governance In A Time Of Complexity And Crisis

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Question 17. What links Steinhoff, McKinsey and KPMG together? A) Fairness B) Accountability C) Failure of governance D) Leadership Question 18. According to the study done how difficult is it to be compliant in SA? A) 25% B) 50% C) 75% D) 30% Question 19. King IV is a statement of principles based on strong ethical leaderships which results in: A) B) C) D)

Ethical culture and legitimacy Successful trading Control over the organization All of the above

Question 20. One of the frequent criticisms of the free market system is the primacy of shareholder interests. A) False B) True


By David Avery, AS, CDT, TE

JDt Business/ManageMent

Operational Management Series

T

he keys to successful product manufacturing are found in the operational aspects of the process. After all, a dental laboratory specializes in one of the most challenging businesses imaginable. The custom nature of what we do requires extremely tight controls if the goal is volume production at a consistent high-quality level. It is well documented that consistency, or the lack thereof, is the primary reason that a dentist changes dental laboratories. Over the next few issues of JDT, I will discuss the basic components necessary for consistent results, regardless of the mix of services in the laboratoryâ&#x20AC;&#x2122;s portfolio. The following is a list of topics we will cover.

Building capacity through the hiring and development of inexperienced talent

David Avery, AS, CDT, TE

Consistency, or the lack thereof, is the primary reason that a dentist changes dental laboratories.

The closures of formal accredited DLT programs over the last 20 years and the aging of the talent pool are leading to a severe shortage of qualified technicians. We will discuss methods to find, qualify, and develop personnel to meet the specific technical standards of the laboratory. The development track for each task group within the laboratory will also be reviewed. At the very core of this segment is the development of work instructions for each procedure. This process will define the specific techniques that serve as the foundation for the laboratoryâ&#x20AC;&#x2122;s custom training program.

The partial or complete adaptation of DAMAS The DAMAS program serves as a great outline for process efficiency, consistency and profit improvement and there is no formal commitment required when purchasing the manual. The NADL reports the sale of over 550 manuals since 2001 and has over fifty laboratories that have gone through third party audits. In this segment we will review the importance of the lean manufacturing process, inventory control and equipment maintenance schedules.

Customer service and retention This area of discussion is often considered a sales and marketing topic. I consider it an operational function first and foremost. In order to accomplish high-quality results every team member must understand that customer service is their responsibility. Satisfied laboratory clients receive a level of support and service that can only come about when a team works together on every level for the benefit of the ultimate customer, the patient. Customer retention is measured in numerous ways and is the ultimate benchmark for how well the laboratory meets customer expectations. The problems that lead to customer loss are always visible with proper understanding of the signs within the manufacturing process. We are transitioning from a handmanufacturing era into the digital-assisted production realm. The information required of any technician remains rooted in the principles of sound function and esthetic acceptance, regardless of the methods utilized.

About the Author David Avery, AS, CDT, TE, received his AAS degree in dental laboratory technology from Durham Technical College in Durham, N.C. in 1976 and served as an executive team member at Drake Precision Dental Laboratory, CDL, DAMAS in Charlotte, N.C for 30 years ending in June, 2015. He actively teaches undergraduate and post-graduate dental students at several universities. Mr. Avery has published in numerous laboratory and clinical journals, serves on many editorial boards. He has presented more than 700 scientific programs for local, regional and national professional clinical and laboratory organizations covering every aspect of dental laboratory technology and communication.

26 Journal of Dental Technology November/December 2017

Published with permission from the JDT November /December 2017 28

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Operational Management Series

1.2 B8

Question 21. What is leading to a severe shortage of qualified technicians? a) aging of the talent pool b) Closures of formal accredited DLT programs c) a and b Question 22 The DAMAS program serves as a great outline for process a) Efficiency b) Consistency c) Some of the above d) All of the above Question 23 Customer service should be considered an operational function and is the responsibility of a) the laboratory owner/manager b) the front office staff c) the dental technicians d) the lab assistants and drivers e) all of the above Question 24 Laboratories are transitioning fromâ&#x20AC;Ś a) b)

a digital-assisted production into a hand-manufacturing era a hand-manufacturing era into a digital-assisted production

Question 25 What is the primary reason that a dentist changes dental laboratories a) Cost of work b) Price of work c) Lack of consistency d) all of the above

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BEWARE: EMPLOYEE MISREPRESENTATION ON CVS IS GETTING WORSE Not surprisingly, considering what we hear every day in the news, employers are finding that candidate employees are more and more embellishing and misrepresenting aspects of their career, as well as omitting embarrassing aspects altogether. It is also getting increasingly difficult to get a thorough picture of a candidate for a position due to increasing restrictions being placed on personal information. This tends to make previous employers nervous to share information on their employees and more and more employers are now giving out no information at all. The consequences of making a mistake when recruiting are damaging as the process is time consuming and adversely affects staff morale, which can lead to a business losing or making less money. A MATTER OF TRUST The relationship between employee and employer is based on trust. Abusing this trust by falsifying a CV breaks down this relationship as the employer begins to doubt what the employee is doing and this usually results in a downward spiral leading to disciplinary hearings and often dismissal. The business then has to start the whole recruitment process again. Labour courts have found that falsifying a CV is a dismissible offence and that there is no need to prove that the misrepresentation led to your decision to appoint the candidate. Whilst this is encouraging, in practice many cases end up being lost by the employer due to some procedural error found by the court. HOW TO DETECT AND DEAL WITH FALSEHOODS IN A CV As noted above, it is becoming harder to obtain the true picture on a prospective staff member. Think perhaps of joining the many companies now using informal networks such as canvassing management in your organisation, or building up Human Resource groups in the applicable industry. Often this approach leads to the employer finding “someone who knows someone” and from there a more accurate picture of the employee’s past can be put together. Why not also pursue someone who commits a dismissible offence – if necessary charge the person and go through the full disciplinary process? Then, be honest with another employer as to why the employee left or was fired. This way at least it will spare other employers making costly appointments and who knows, it may begin to spread throughout the sector and come back to benefit your business directly one day.

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Beware: Employee Misreprensentation On Cvs Is Getting Worse

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Question 26. Why is it getting increasingly difficult to get a thorough picture of a candi date applying for a position? A) B) C) D)

Candidates withholding information Poorly prepared CVS Misrepresentation of candidate Increased restrictions of candidate personal information

Question 27. The consequences of making a mistake when recruiting are damaging as the process is time consuming and can lead to making or losing money. A) False B) True Question 28. According to this article the relationship between employee and employer is based on: A) Trust B) Salary C) CVS D) Skill Question 29. How does the writer of this article suggest one to deal with false information in a CV? A) B) C) D)

Canvassing management in your organization Building up human resource groups Someone who knows someone All of the above

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Case Study Using inCoris CC™ Sinter Metal, and the inLab system Rehabilitation of a Full Mandible - All on Six Restoration Darron Chidrawi B-Tech Dental Technology, Dental Evolution Laboratory, Cape Town

Keywords: Sinter Metal, CAD/CAM, Mandibular support bar, Hybrid Over-denture

Abstract Patient: A 55 year old female patient with a full upper and lower hybrid over-denture on implants. The support bar on the lower fractured and needed to be replaced.

The Challenge: The original support bar was manufactured from PEEK. [Polyether ether ketone] This bar broke due to the patient’s loss of proprioception. The bite was harder than anticipated and therefore a stronger material was required for the replacement bar. The patient grew accustom to the light weight of original restoration. A solution had to be found that would allow for a strong, light weight restoration, which could be designed inside the hybrid overdenture.

The Treatment: It was decided to manufacture the replacement bar in inCoris CC™ sinter metal to give the necessary strength to the over-denture. Using the inLab system a bar could be designed with the precision needed to fit inside the over-denture.

Introduction: The fact that Dentsply Sirona offer both the CAD/CAM system to design the replacement bar, and inCoris CC™ sinter metal material for manufacturing, made this system the obvious choice to use for this case. The original scan in inLab 16 software, was used to re-design the bar after which it was milled and processed in inCoris CC™ sinter metal material. The finished replacement bar was scanned on the inEos inLab scanner, after polishing. The hybrid over-denture framework was re-designed using a bio-copy of the original framework, in inLab 16 software. This was then milled from PEEK material and 12 individual lithium disilcate crowns were placed on the framework. The PEEK framework gives a shock-absorbing benefit which is important in this case as both upper and lower restorations are done on implants.

Figure 1: Old denture in the pa-

Figure 2: First replacement hybrid

tient’s mouth.

restoration of which the bar fractured

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Figure 3: Dry milling of PEEK framework in MC X5™, 5 axis milling unit. Separate water tank and special burs used.


milling. Superior smooth finish.

Figure 5: Bar after designing in the inLab 16 software.

Figure 6: inCoris CC™ 98mm disk loaded in the MC X5™, 5 axis milling machine, ready to be milled

Figure 7: Replacement bar just after wet milling was finished.

Figure 8: Bar was dried in an airfryer at 80˚for 30 minutes.

Figure 9: Restoration in a separate firing bowl and firing beads, intended for sinter metal firing.

Figure 10: Restoration after it has been fired in the inFire™ Sintering Furnace with Argon Gas.

Figure 11: A 100% passive fitting bar on the model.

Figure 12: Sinter metal bar after it

Figure 12: Finished bar was scaned

Figure 13: Proposal of the crowns

in again on inEos X5™ scanner for accuracy as the bar was polished by hand after processing.

that would be placed on top of the hybrid structure. Crowns were virtually seated on the gingival element of the design.

Figure 14: Hybrid frame with gingival element, after cutback for the crowns has been done, to prepare for the individual crowns that will be placed on top of the structure.

Figure 15: Top view of the stumps

Figure 16: in Coris CC™ bar fits

Figure 17: Final product in the pa-

on the hybrid structure.

snuggly in the PEEK framework.

tient’s mouth.

Figure 4 : PEEK framework after

has been worked off and polished.

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Conclusion: The initial failure of the support bar in this case resulted in a most unfortunate situation where the clinician lost faith in his laboratory. This is greater than any monetary loss. The inLab sytem coupled with inCoris CC™ sinter metal delivered a world class solution, and restored faith to all parties. The laboratory technician was pleased with the ease of use of the inCoris CC™ material. This process was noticeably cleaner and easier to work with, than a regular casted bar. The bar fitted 100%, which is very difficult, if not impossible to achieve with a traditionally casted bar. This is a massive benefit and stress reliever. Another major benefit to creating bars utilizing the inLab system is that the proces is repeatable and the outcome predictable. The completed inCoris CC™ bar weighed a mere 11g, and the total finished case with crowns was only 15g heavier than the original case. The weight of the total lower hybrid bar was only 30g. The patient was very pleased with the replacement as it was still light weight, and offered the same shock-absorbing qualities of the original hybrid while the aestetics where not compromised in any way. Overall a very good comeback from a very difficult situation, thanks to the complete system from Dentsply Sirona.

References: 1. 2. 3.

Dentsply Sirona inCoris CC; Sintering metal for inLab; 64 50 295; D3487.201.08.03.02 10.2016. Dentsply Sirona inLab MC X5 Operating Instructions; 64 78 759; D3608.201.01.07.02 10.2017. https://www.dentsplysirona.com/en/products/cad-cam/dental-lab/cad-cam-materials/func tion-esthetics/incoris-cc-incoris-ccb.html

More about inCoris CC™ Applications for inCoris CC™ inCoris CC™ can be used to produce PFM crowns and bridges. Any procelain that has a compatible CTE can be used to layer the material.

The advantages of inCoris CC™ include: Speed of the process Quality and accuracy of the restorations produced The safty of the process due to wet milling The clean, purely digital workflow The speed of the process,

Technical Data - inCoris CC™ The following specifications apply to material that is densely sintered in an inFire HTC speed sintering furnace with metal function. Type

NPM ceramic alloy (NPM=Non-Precious Metal)

Hardness according to Vickers: 225 ± 20HV 0.2% yield stress > 480 MPa Tensile strength: > 850 MPa Elasticity module: 80 ± 20GPa Elongation at break > 20% Density 7.6g/cm3 Solidus point 1,360 °C Liquidus point 1,400 °C CTE value: 14.5 ± 0.5mɥ/m·K Measurement performed on samples according to DIN EN ISO 22674

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“Using inCoris CC™ sinter metal with the inLab system is 100% peace of mind dentistry. What you put in, is exactly what you will be getting out. Fantastic results!” Darron Chidrawi Dental Evolution Laboratory Cape Town.


Using inCoris CC Sinter Metal and the inLab system Question 30: The final bar made of sinter metal was significantly heavier than the original bar manufac tured from PEEK. a) True b) False Question 31: Which of the following statements are true: A B C

The replacement bar was manufactured by re-scanning the model and re-designing the bar on the software. The hybrid over denture was designed together with the support bar utilizing one scan. The replacement bar was re-designed on the original scan.

Question 32: How many of the following statements are true: A B C

The sinter metal used were dry milled and sintered in a special firing bowl with sinter beads intended for metal sintering. The sinter metal is only indicated for metal restorations where no porcelain has to be layered on it. The sinter metal used was fired with Argon Gas.

a) b) c)

All three Two of the statements Only one

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inLab MC X5

Dental lab freedom of choice Disks & blocks. Milling & grinding. Wet & dry. The 5-axis laboratory production unit inLab MC X5 is your universal CAD/CAM partner for a wide range of indications â&#x20AC;&#x201C; with complete freedom to use any material and flexible STL integration into existing CAD systems. Its own CAM module and functional design guarantee a high degree of user-friendliness and effective production processes. New: Clean and safe milling of NPM sintering metal blanks inCoris CCB with the inLab MC X5 based on digital restoration data.

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DENTASA Summit 2018

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Find DENTASA here:

https://www.facebook.com/groups/dentasa/

@DENTASA

www.dentasa.org.za

dentasa@absamail.co.za Phone: 012-460 1155 Fax to email: 086 233 7122 Office Hours: Mon-Fri 08:00-13:00 Southern African Dental Technology Journal COPYRIGHT©

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