Trends in Prosthodontics and Dental Implantology

TRENDS IN PROSTHODONTICS AND DENTAL IMPLANTOLOGY An official Publication of the Department of Prosthodontics AECS Maaruti College of Dental Sciences and Research Centre, Bangalore January - June 2010 | Vol. 1 - Issue No. 1

Editor Dr. Jayakar Shetty M.

Consultant editor Dr. K. Chandrasekharan Nair

Associate editors Dr. Vahini Reddy Dr. Divya Hegde

Assistant editors Dr. Lakshmikanth K. Dr. Tabreen Aiasha Dr. Srividya S. Dr. Chiranjeevi Reddy

Advisors Sri. R. Venkatesh

Contents Evaluation and comparison of surface detail reproduction of different elastomeric impression materials under dry and wet conditions

5

Dr. Tabreen Aiasha

While meeting the patient’s mind, do we really forget our mind

9

Dr. Div ya Hegde

Fabricating ceramic posts using CAD/CAM technology

11

Dr. Srividya S.

(Secretar y, AECS)

Dr. Ramchandra C.S. (Principal)

Dr. Ravindra Savadi Dr. Purushotham Manvi Dr. Shivashankar

Editorial Office Dept. of Prosthodontics AECS Maaruti College of Dental Sciences and Research Centre 108, BTM 6th stage, I Phase, Hulimavu Tank Bund Road, Off Bannerghatta Road Bangalore - 560076 Tel:09448064349 Fa x: 080-26587159 E-mail: trendsinprosthodontics@gmail.com

Evaluation of the effect of wetting agents on gypsum dies made on polyvinyl siloxane impression materials: An in-vitro study

14

Dr. Lakshmikanth K.

Good Teacher

18

Dr. Chandrasekharan Nair K.

A review on the design and Surface characteristics of modern dental implants

22

Dr. Jayakar Shet t y

In Short

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Designing and Printing Suman Graphics, Trivandrum E-mail: sumangf x@gmail.com For Private circulation only

TPDI • Januar y 2010, Vol. 1, No. 1 •

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AECS Maaruti College of Dental Sciences and Research Centre 108, BTM 6th stage, I Phase, Hulimavu Tank Bund Road, Off Bannerghatta Road, Bangalore - 560076

Sri.R.Venkatesh

Message I am very happy to learn that the Department of Prosthodontics is bringing out a speciality Journal during the month of January 2010.

I am aware that a lot of research work is happening in my college and the department of Prosthodontics has a pioneering role. By publishing this journal, the research findings can be brought to the notice of the fraternity without much delay. While assuring you all possible cooperation, I am sending my best wishes for the forthcoming journal.

Sri.R.Venkatesh Secretary

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TPDI • January 2010, Vol. 1, No. 1 •

Brig. (Dr.) Anil Kohli

Message I am indeed happy to learn that the Postgraduate department of Prosthodontics, AECS Maaruti College of Dental Sciences and Research Centre, Bangalore is going to publish a journal entitled ‘Trends in Prosthodontics and Dental Implantology’ and releasing the first issue during the second week of January 2010.

Dentistry in India is presently facing a fast developing pace and the quantum of research happening is enormous. The findings of research should be published without much delay and hence there is enough scope for research publications. Dental Council of India has taken firm and positive steps to make sure that the teaching faculty involve in research and have publications and presentations. I hope Trends in Prosthodontics will be a trend setter in upholding the highest standards. This message carries my best wishes.

Brig. (Dr.) Anil Kohli President, DCI

TPDI • January 2010, Vol. 1, No. 1 •

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Editorial

shett yjayakar@gmail.com chandrasekharannair.drk@gmail.com

Dr. K. Chandrasekharan Nair

Dr. Jayakar Shetty M.

In the 19th century, the mechanistic influence was greater on Prosthodontics and it has recognized its biologic basis during the 20th century. This happening can be considered as one of the important markers of evolution in Prosthodontics. The study of occlusion, increasing use of evidence-based treatment, development of adhesive techniques and the emergence of dental implantology have dramatically changed the profile of Prosthodontics. In the 21st century the pervasive influence of digital computing technology has shown its influence on Prosthodontics, as the specialty has always been at the forefront of technological innovation. We cannot think of modern prosthodontic treatment without digital technology, in view of the increasing population, increasing scientific data, accurate diagnostic requirements of dental implant treatment and the CAD/ CAM based fabrication of prosthesis. Very soon we expect a robotic invasion into our profession.

We are very glad to give a rosy picture of the evolution of our profession. At the same time we recognize the fact with great concern that in this development, the contribution of India is negligible. No doubt we provide a decent market to the contributions of other countries. We cannot contribute because we do not do original research. To be precise we don’t intend to do. In this context we are reminded of a statement made by a senior professional (in a lighter vein) that ‘without a key article from a foreign journal how can you do a thesis’. Sixty two years ago we got independence but still we have not obtained intellectual independence. Indian dental research is always snubbed due to the lack of publication avenues. Hundreds of postgraduates come out of very prestigious institutions and very seldom these youngsters take up research in their future career. Sadly we do not have proper patient statistics and our prosthodontic treatment needs cannot be calculated. We seldom find a document showing the extent of edentulism prevailing in our country. All these circumstances have compelled us to publish a prosthodontic journal entitled ‘Trends in Prosthodontics and Dental Implantology’. Hope this provides adequate stimulus to dental research and avenue for publication.

Dr. Jayakar Shetty M. Dr. K. Chandrasekharan Nair

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TPDI • January 2010, Vol. 1, No. 1 •

Research Evaluation and comparison of sur face detail reproduction of dif ferent elastomeric impression materials under dry and wet conditions Tabreen Aiasha * Surendra Kumar G.P.** Ravindra C. Savadi***

Abstract Statement of Problem: The hydrophobic nature of poly vinylsiloxane and polyether elastomeric impression material.

Purpose: The aim of the study was to compare surface detail reproduction of 2 hydrophilic poly vinyl siloxane (PVS) and two polyether (PE) impression materials under dry and wet conditions.

Materials and methods: 128 impressions were made from light body and medium body of hydrophilic PVS and PE impression material under dry and wet condition from Stainless steel metal dies similar to those described in American Dental Association (ADA) specification 19. Surface detail was evaluated by two methods (1) by use of criteria similar to ADA specification 19, continuous replication of at least 2 of 3 horizontal lines and (2) by use of surface characterization such as presence of pits, voids or roughness on the surface of the impressions. The detail reproduction was statistically analyzed using Pearson’s chi square test.

Results: The surface detail evaluation indicated that moisture had a significant effect on detail reproduction of both PVS and PE materials. Under dry conditions all 4 materials had satisfactory detail reproduction for all the samples, however under wet conditions only 12.5% of PVS and PE light body and 25% of PVS medium body were satisfactory and all the samples of PE medium body were unsatisfactory. For the additional surface detail characterization, impressions were satisfactory only under dr y conditions that is 87.5% of light body and 81.3% of medium body of PVS, 81.3% of light body and 87.5% of medium body of PE were satisfactory.

Conclusion: Within the limitation of this study, it could be concluded that satisfactory surface detail reproduction were obtained only under dry conditions.

A

* Senior Lecturer, Dept of Prosthodontics, AECS Maaruti College of Dental Sciences and Research Centre, Bangalore ** Professor, V.S. Dental College, Bangalore *** Prof. & HOD, Dept. of Prosthodontics, Oxford Dental College, Bangalore e-mail: drtabreenaiasha@gmail.com

significant limitation of vinyl polysiloxane impression materials is the hydrophobicity. Hydrophobic nature of vinyl polysiloxane impression material is expressed both in the liquid phase and in the polymerised solid phase and related to the surface energy. In the former, the impression material will not wet the tissue surface and in the latter the gypsum will not wet the impression material. In contrast to vinyl polysiloxanes, polyether impression materials are more hydrophilic. Both polyether and vinylpolysiloxane added with hydrophilic surfactants TPDI • January 2010, Vol. 1, No. 1 •

are expected to demonstrate adequate wetting of moist oral tissues and tooth surfaces. Sufficient data is not available to prove that moist surfaces will be copied by these impression materials. A few studies have been conducted and the results of which showed that the dry, moist, and wet conditions did not cause significant adverse effects on the dimensional accuracy of either material. However surface details were copied better only under dry conditions for both the materials1,2,3.

A comparative evaluation of the effect of dry and wet conditions on the copying capability of PVS and 5

Tabreen Aiasha

Fig. 1. Stainless steel metal dies

Fig.2. Satisfactory impressions of line reproduction

Polyether materials was not done. Hence objective of the present investigation was to evaluate and compare surface detail reproduction of two hydrophilic vinyl polysiloxane and two polyether impression materials when used under dry and wet conditions.

Materials and methods Two standardized stainless steel dies similar to those described in ADA specification 19 were machined 4 (figure 1). Three horizontally ruled lines x, y and z for detail reproduction were inscribed on the superior surface of the die. The distance between x and z is 5 mm. The width of the lines was 0.020 mm. The dies were labeled as 1 and 2 and each die was assigned to one of the two conditions, dry and wet respectively.

The dies have stainless steel rings that fit around the borders as a mold for the impression material and also have stainless steel raisers that aids in the impressions to be pressed out from the mold.

The impression materials used in this study were hydrophilic polyvinyl siloxane (Imprint TM II) and polyether (ImpregumTM soft) in light and medium body viscosities. A total of 128 impressions of the die were made in dry and wet condition. These were divided into two groups, polyvinyl siloxane and polyether. 64 impressions were made in polyvinyl siloxane and polyether, in which 32 each were made with light body and medium body and in that 16 impressions were made under each of the two conditions dry and wet.

For impressions made under dry conditions, mold was placed on the beveled edges of the die to contain the material and ensure a uniform thickness of 3 mm.

Polyvinylsiloxane (light body and medium body) was dispensed on the die with an automixing syringe. For Polyether, equal lengths of base and catalyst of Impregum light body and regular body were hand mixed. For making impressions under wet conditions, the metal die was immersed in artificial saliva before the application of the impression material. With the tip of the syringe and/or spatula under artificial saliva the material was injected onto the surface of the die. A polyethylene sheet and glass plate was placed on top of the mold to contain the material and a weight of 500 6

grams was applied. To compensate for polymerization at room temperature rather than at mouth temperature, the impressions were allowed to set for twice the manufacturer’s recommended setting time as indicated in ADA specification 19 for laboratory testing2.

The light body and medium body of polyvinyl siloxane (ImprintTM II) were recovered from the water bath after 8 minutes. Light body and medium body polyether (Impregum TM soft) was recovered from the water bath 6 minutes and 7 minutes respectively after the material was first applied onto the die. After each impression was allowed to air dry, a numeric coding system was used to ensure blind evaluation.

Evaluation of surface detail reproduction Surface detail reproduction was evaluated immediately after the impressions were recovered.

Evaluation was done using two methods. The first evaluation was an assessment of the continuity of the line replication. All the 3 lines were assessed for each specimen. If at least 2 of the 3 horizontal lines were reproduced continuously between cross points, the impression was considered satisfactory (figure2). All others were rated unsatisfactory. In the second method, macroscopic evaluation of the impression surface was done to evaluate surface characteristics such as roughness, pits and voids on other areas of the impression.

Impressions were rated satisfactory if the entire impression surface was smooth, shiny and free of voids or pits and impressions were rated as unsatisfactory if the impression surface was rough or contained any pits or voids.

The data obtained were analyzed by two way analysis of variance (ANOVA) and Pearson’s Chi Square Test. The results are presented graphically as bars.

Results Comparison of all the 4 materials for dry and wet conditions has a significant effect on detail reproduction.

Under dry conditions impressions made from PVS (light body), PVS and PE (medium body) were 100% (16/ 16) satisfactory and impressions made from PE (light body) were 93.8% (15/16) satisfactory, which is

TPDI • January 2010, Vol. 1, No. 1 •

Evaluation and comparison of surface detail reproduction of dif ferent elastomeric impression materials under dr y and wet conditions

Fig. 4. Impressions of PVS light body, under dry condition(LBDC) which satisfactorily reproduced the lines were 100% and satisfactorily smooth surface evaluation was 87.5%.

Impressions of PVS light body, under wet condition(LBWC) satisfactorily line reproduced were 12.5% and none of the impressions had a smooth surface under wet condition

Fig. 5. Impressions of PVS medium body, under dry condition(MBDC) which satisfactorily reproduced the lines were 100% and satisfactorily smooth surface evaluation was 81.3%%.

Impressions of PVS medium body, under wet condition (MBWC) satisfactorily line reproduced were 25% and none of the impressions had a smooth surface under wet condition

Fig. 6. Impressions of PE light body, under dry condition (LBDC) which satisfactorily reproduced the lines were 93.8% and satisfactorily smooth surface evaluation was 81.3%.

Impressions of PE light body, under wet condition(LBWC) satisfactorily line reproduced were 12.5% and none of the impressions had a smooth surface under wet condition

Fig.7 Impressions of PE Medium body, under dry condition (MBDC) which satisfactorily reproduced the lines were 100% and satisfactorily smooth surface evaluation was 87.5%.

None of the impressions of PE medium body, under wet condition (MBWC) reproduced the lines and the smooth surface satisfactorily.

reproducing at least 2 of the 3 lines continuously. Under wet conditions only 12.5% (2/16) of PVS and PE light body, 25 % (4/16) of PVS medium body were satisfactory. All the impressions of PE medium body in wet conditions were unsatisfactory.

A statistically significant effect was observed for additional macroscopic evaluation of the impression surfaces, the produced impressions were rated as satisfactory or unsatisfactory based on the presence or absence of voids or pits on the entire surface of the impression. Under dry conditions 87.5% (14/16) of light body and 81.3% (13/16) of medium body of PVS, 81.3 % (13/16) of light body and 87.5% (14/16) of medium body of PE were smooth and shiny. Under wet conditions all the materials failed to reproduce acceptable impressions as all impressions had pits and voids. The graphical and tabular representation of both the criteria of evaluation of surface detail reproduction in percentage are presented in figure 4, 5, 6 & 7 and Table I and II.

Discussion Detail reproduction of the impressions made under dry and wet conditions were evaluated according to criteria similar to ADA specification no. 19. The specification states that an elastomeric impression material should be able to continuously replicate 1 of the 0.02 mm horizontal lines in 2 of 3 specimens. In this in vitro study a slight modification was made to assess detail

reproduction where in continuous replication of at least 2 of 3 horizontal lines on each specimen were assessed.

The light and medium body of PVS (IMPRINTTM II) and Polyether (IMPREGUMTMSOFT) could meet this criterion for all the samples only under dry condition.

In contrast the light and medium body of PVS (IMPRINTTM II) and Polyether (IMPREGUMTMSOFT) could meet this criterion only 12.5% (2/16) of the time under wet condition. That is both materials performed unsatisfactorily under wet conditions.

An additional evaluation to assess the smoothness of the impression surface was also done. If pits and voids were present on the impression surfaces then the impression was considered unacceptable. The results of this smooth surface evaluation were not consistent with the results of detail reproduction based on continuous replication of lines. All the 4 impression materials produced smooth and shiny impressions under dry condition and failed to produce smooth impressions under wet conditions. This additional evaluation in this study suggested that a dry field is obligatory to produce clinically acceptable impressions.

The results of this in vitro study suggest that the clinician using these materials should maintain strict moisture control during impression making as the so called hydrophilic PVS remain hydrophobic in the unpolymerized state and cannot adequately wet surfaces covered with moisture. Although the additive surfactants have improved the polymerized PVS wettability with

TPDI • January 2010, Vol. 1, No. 1 •

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Tabreen Aiasha

Table I. Percentage of satisfactor y and unsatisfactor y impressions according to criteria based on ADA specification 19 for acceptable sur face detail reproduction

Impression Materials PVS (Light body)

PVS (Medium body)

PE (Light body)

PE (Medium body)

Condition Satisfactory Un satisfactory (n = 16) (%) (%)

Dry Wet

100 12.5

0 87.5

Dry Wet

100 25

0 75

Dry Wet

93.8 12.5

6.3 87.5

Dry Wet

100 0

0 100

dental gypsum products, it appears that the impression materials cannot accurately reproduce detail in presence of moisture. PE as itself being hydrophilic also lacks to reproduce detail in wet conditions.

As laboratory testing cannot exactly simulate in vivo conditions, the results of an in-vitro investigation must be viewed with caution. In this in vitro study impressions were made on standardized stainless steel dies which were calibrated for precise comparisons, yet they do not resemble the behavior of the oral tissues, for example metal dies do not absorb liquids. In addition, intrinsic surface free energy of a metal die will be much higher than the surface free energy of the proteinaceous surfaces of the prepared teeth and oral soft tissues. Even though the surface free energy and chemical structure of the unpolymerized impression material is critical to the material’s ability to wet the impressed surface, the energy of the impressed surface will also influence surface wettability.

This investigation helps in understanding the limitations of hydrophilic PVS and PE impression materials when used to record the surface detail of wet oral substrates. But the wet surface method used in this study in which the dies were place in artificial saliva before the impressions were made was a worst case scenario.

This is in contrast to the oral tissues where there is water at the surface and within the bulk of the tissues and the water within the bulk of the tissue can diffuse to the surface during recording of an impression. It would be very difficult to duplicate this type of moisture contamination in the laboratory, but it does indicate that there are other sources of water present in the mouth that could interfere with the recording of impressions.

The experimental method used in this study should

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Table II. Percentage of satisfactor y and unsatisfactor y impressions

Impression Materials PVS (Light body)

PVS (Medium body)

PE (Light body)

PE (Medium body)

Condition Satisfactory Un satisfactory (n = 16) (%) (%)

Dry Wet

87.5 0

12.5 100

Dry Wet

81.3 0

18.8 100

Dry Wet

81.3 0

18.8 100

Dry Wet

87.5 0

12.5 100

be considered as a preliminary testing of the accuracy and behavior of the hydrophilic impression materials.

Conclusions This study compared the surface detail reproduction of PVS and PE. Within the limitations of this in vitro study, the following conclusions can be drawn 1. Both hydroplilic polyvinylsiloxane and polyether tested satisfactorily with respect to detail reproduction only under dry conditions but not under wet conditions when evaluated according to criteria similar to ADA specification No.19.

2. Further evaluation of the impressions smooth surfaces revealed that both materials performed satisfactorily under dry conditions but were unsatisfactory under wet conditions.

References 1. Walker, Petrie CS, Haj-Ali R, Spencer P, Dumas C, Williams K. Moisture effect on polyether and poly vinylsiloxane dimensional accuracy and detail reproduction. J Prosthodont.

2005 Sep; 14(3):158-63.

2. Dimensional accuracy and surface detail reproduction of two hydrophilic vinyl polysiloxane impression materials tested under dry, moist, and wet conditions. J Prosthet Dent. 2003 Oct; 90(4):365-72.

3. Pratten DH, Craig RG. Wettability of a hydrophilic addition silicone impression material. J Prosthet Dent. 1989 Feb; 61(2):197-202.

4. Revised American Dental Association specification No. 19 for Non Aqueous, elastomeric dental impression materials. JADA, Vol 94, April 1977, 733- 741.

TPDI • January 2010, Vol. 1, No. 1 •

Patient management While meeting the patient’s mind, do we really forget our mind Divya Hegde * Chandrasekharan Nair K. ** Jayakar Shetty ***

* Associate Professor ** Professor and Head of the Depar tment Department of Prosthodontics ***Professor and Head of the Depar tment Department of Implantology AECS Maaruti College of Dental Sciences and Research Centre Bangalore e-mail: divi912@gmail.com

ilus M. House is credited with devising a method to describe the mental attitudes of complete denture patients and its acceptability is unchallenged till recent times. M.M. House classified patients as philosophical, exacting, hysterical and indifferent. House classification has a limitation that its basis is on the behavioral pattern of the patients when they encounter the reality of edentulism. The reactive nature would probably give us an insight into their adaptive capability to wear dentures.

However it does not include the dentists emotional reaction to the patient’s behaviour which can greatly influence the assessment. A revalidation of patient’s character in view of dentist’s mental make up becomes relevant in the context of modern needs. This paper describes a system of classification which can be considered as realistic. Primarily dentist-patient relation has to be considered as a singular unit. Unilateral classification including only the patient lacks validity.

towards doctor, patients are classified as Ideal, Submitter, Reluctant, Indifferent and Resistant1.

The ideal patient has reasonable attitude and hence trusts the doctor and the treatment. The submitter patient has a tendency to idealize the doctor and hence he never distrusts the doctor and the treatment. The reluctant patient is skeptical about the treatment plan. Though these patients trust the treatment, the element of doubt will always be maintained. Indifferent patient has not visited the dentist on his own but through pressure from someone.

Naturally he will not trust the treatment or the doctor. Resistant type of patients will be challenging the doctor and there is no trust.

Doctor patient relation

Doctor type and Ego state

M

The doctor patient relationship is determined by the comfort level enjoyed by both of them. The perception of the doctor about the patient or the perception of the patient about the doctor is interrelated or rather mutual. It is important to learn the behavioral science to have good interpersonal relationship with the patient. Unless we understand the mind of the patient, we will not be able to identify the needs of the patient and provide satisfactory treatment.

Behavioral profile of the patients Based on the attitude and trust TPDI • January 2010, Vol. 1, No. 1 •

Patient type

Attitude

Trust

Ideal Submitter Reluctant

Reasonable Idealized Skeptical

Indifferent

Coerced to see the doctor Challenges

Reasonable Surrenders Trusts but doubtful No trust

Resistant

No trust / argues

Eric Berne developed Parent/ Adult/Child (PAC) model of ego states. These are the mixture of behavior, thoughts and feelings.

Parent ego: people think and behave like their own parental figures did in their childhood. This is a set of feelings, thinking and behaviour that we have copied from our parents and other significant people.

As we grow up we take in ideas, beliefs, feelings and behaviours from our parents and caretakers. If we live in an extended family then there are more people to learn and take in from. When we do this, it is called introjecting and it is just as if we take in the whole of the care giver. For 9

Div ya Hegde

Reactions of the dentist to each patient type Patient type

Ideal doctor

Gospel speaker

Dominating

Ideal

Ideal

Not pleased

Less enthusiastic

Submit ter

Doubt ful

Feels highly respected

Feels ideal

Reluctant

Of fended or challenged

Offended or occasionally challenged

May win over or frustrated

Indifferent

May consider as personal failure

Frustrated

Irritated or may disengage

Resistant

Angry or disappointed

Feels disrespected

Confrontation

example, we may notice that we are saying things just as our father, mother, grandmother may have done, even though, consciously, we don’t want to. We do this as we have lived with this person so long that we automatically reproduce certain things that were said to us, or treat others as we might have been treated.

Adult ego: always rational, willing to find out more and analyzing everything. The Adult ego state is about being spontaneous and will have the capacity for intimacy.

When in our Adult we are able to see people as they are, rather than what we project onto them. We ask for information rather than stay scared and rather than make assumptions. Taking the best from the past and using it appropriately in the present is an integration of the positive aspects of both our Parent and Child ego states.

So this can be called the Integrating Adult. Integrating means that we are constantly updating ourselves through our every day experiences and using this to inform us. A good doctor will always maintain an adult ego state in the interactions with the patient.

Child ego: people behave, feel and think similarly to how they did in the childhood. The Child ego state is a set of behaviours, thoughts and feelings which are replayed from our own childhood. Perhaps the boss calls us into his or her office, we may immediately get a churning in our stomach and wonder what we have done wrong. If this were explored we might remember the time the head teacher called us in to tell us off. Of course, not everything in the Child ego state is negative.

We might go into someone’s house and smell a lovely smell and remember our grandmother’s house when we were little, and all the same warm feelings we had at six year’s of age may come flooding back. Both the Parent and Child ego states are constantly being updated.

For example, we may meet someone who gives us the permission we needed as a child, and did not get, to be fun and joyous. We may well use that person in our imagination when we are stressed to counteract our old ways of thinking that we must work longer and longer hours to keep up with everything. We might ask ourselves “I wonder what X would say now”. Then on hearing the new permissions to relax and take some time out, do just that and then return to the work renewed and ready for the challenge. Subsequently, rather than beating up on ourselves for what we did or did not do, what

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tends to happen is we automatically start to give ourselves new permissions and take care of ourselves. Alternatively, we might have had a traumatic experience yesterday which goes into the Child ego state as an archaic memory that hampers our growth. Positive experiences will also go into the Child ego state as archaic memories. The positive experiences can then be drawn on to remind us that positive things do happen. The process of analysing personality in terms of ego states is called structural analysis. It is important to remember that ego states do not have an existence of their own, they are concepts to enable understanding. Therefore it is important to say “I want some fun” rather than “My Child wants some fun”. We may be in our Child ego state when we say this, but saying “I” reminds us to take responsibility for our actions. Doctor type and ego status of the each doctor type is classified as Ideal (adult ego state), Gospel speaker (Parent ego state) and Dominating (Parent ego state- critical). The doctor with adult ego state will be analyzing everything and willing to find out more. The doctor with the parent ego might demand unquestioning, submissive and obedience behavior of the patient.

Doctor with parent ego state who is critical might be one who wishes to be pleased and when pleased might reward the child. He can react covertly and even get frustrated can have a co-operative relationship with the patient to satisfy the requirements.

Conclusions Presently patient’s mental status is classified without considering the personality of the doctor. In doctorpatient relation both the components are equally important. Assessment of patient’s personality will be influenced by the doctor’s personality. Knowledge of ego states is a must for successful practice. Mind and its evaluation is not simple but really complex. While meeting the patient’s mind we have to consider our own mind and be aware of the ego states.

References 1. Gamer, Tuch and Garcia. M.M.House mentalclassification revisted: Intersection of particular patient types and particular dentists need. J Prosthet Dent 2003; 89:297-302.

2. Winklers S, Psychological aspects of treating complete denture patients: their relation to prosthodontic success. J Geriatr Psychiatr y Neurol 1989; 2:48-51

TPDI • January 2010, Vol. 1, No. 1 •

Technology Fabricating ceramic posts using CAD/CAM technology Srividya S. * Chandrasekharan Nair K. ** Jayakar Shetty *** Shivshankar ****

* Senior Lecturer, **Professor and Head of the Department of Prosthodontics,*** Professor and Head of the Department of Implantology, AECS Maaruti College of Dental Sciences and Research Centre, Bangalore**** Professor, Krishnadevaraya Dental College and Director-Confident Laboratories, Bangalore e-mail: drsrividya5@gmail.com

T

hemost common type of failure of endodontically treated tooth is post loosening 1 . This can be due to selection of improper post system.

While selecting a post system, the root canal morphology of the tooth being restored should be considered.

In case of narrow canals with adequate dentinal wall thickness, a prefabricated post shows better adaptation to the canal walls. Narrow canals are common in posterior teeth. However if a prefabricated post is used in case of wide circular canals with thin dentinal walls, it will have to depend on the increased thickness of cement for its retention.

This cement layer may not be able to provide adequate retention for the post because of the nature of forces exerted on the anterior teeth. Hence, for the maxillary anterior teeth with wide circular canals, a custom made post is considered the gold standard of care. Custom made posts provide better adaptation to the prepared canal wall2. Custom made posts are of two types viz. custom made metal post, ceramic post obtained from CAD/CAM technology. All ceramic crowns are now replacing the metal ceramic crowns in the anterior region. While restoring an endodontically treated anterior tooth with an all ceramic crown, it’s prudent to use a esthetic post system. The currently available CAD/CAM system, use alumina or partially sintered zirconia blocks to mill a post and core3. This article describes in detail the procedure of obtaining a custom made post from a partially sintered zirconia block using CAD/CAM system.

TPDI • January 2010, Vol. 1, No. 1 •

Procedure After the obturation is completed, the tooth is prepared to receive an all ceramic crown. Then the post space is prepared using gates glidden drill and peeso reamer alternatively. The canal is finally enlarged to the width of the widest peeso reamer or gates glidden drill.

The length of post should be equal to or greater than the length of the crown or should be between one half and three quarters of the length of the root. A minimum of four to five millimeters of root canal filling material must be retained as apical seal. The thickness of remaining dentinal wall should be atleast 1 mm. An antirotation groove is placed on the thickest dentinal wall.

The prepared post canal space is cleaned with normal saline and dried with absorbent paper point. The prepared canal walls should be smooth and free of undercuts. An autopolymerising acrylic resin pattern is prepared to be sent to the laboratory. First an autopolymerising acrylic resin rod is prepared and then placed in the canal to check the adequacy of the length of the post.

Separating media is applied on the internal surfaces of the prepared canal walls. Autopolymerising acrylic resin mixture is painted to the surface of the acrylic rod and placed in the canal and checked for the fit. This procedure is repeated until the post resin pattern has good adaptation and fits in passively without binding to the prepared canal wall. The post pattern is placed inside the canal and core is built using autopolymerising acrylic resin. Once the material has set, the core is prepared. Then the prepared post resin pattern is sent to the laboratory.(Fig 1) 11

Srividya S.

Fig. 1 Autopolymerising acrylic resin post pattern

Fig. 4 The scan element with the resin pattern is inserted into the scan slot in the Inlab MCXL machine.

Fig. 2 Resin pattern is attached to a special scan element for scanning using hard wa x.

Fig. 3 Contrast media is sprayed on to the resin pattern

Fig. 5 Scanned images of the resin pattern

Fig. 6 Three Dimensional image of the resin pattern seen on the computer monitor

Fig. 8 Partially sintered zirconia block attached to the scan element is inserted into the scan slot in the Inlab MCXL machine.

Fig. 9 Bar code read by the scanner

Fig. 7 Partially sintered zirconia block with barcode which gives information to the software about the shrinkage ratio of that particular zirconia block

Fig. 10 Post and core being milled in the Inlab MCXL machine from the partially sintered zirconia block.

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Fig. 11 Milled post and core

TPDI • January 2010, Vol. 1, No. 1 •

Fig. 12 Milled post and core placed in a carrier containing zirconia balls for sintering

Fabricating ceramic posts using CAD CAM technology

Lab procedure of making a CAD/CAM post and core from partially sintered zirconia block using Cerec Inlab.

The resin pattern is attached to a special scan element for scanning wax patterns directly using a hard wax (Fig

Fig. 13 Milled post and core placed in furnace for sintering

2). A contrast media is sprayed on to the resin pattern (Fig 3) The scan element with the resin pattern is inserted into the scan slot in the Inlab MCXL machine and in the software the command is given as wax pattern scan (Fig 4). The machine will start scanning the pattern in 6 different angles to construct an exact 3 dimensional image (Fig 5, 6). Once the scan image is obtained it is processed in the software and then the mill command is given after inserting the suitable zirconia block in the milling machine.

The milling machine first scans the barcode which will be printed on every Zirconia block which gives information to the software about the shrinkage ratio of that particular zirconia block (Fig 7,8,9). The software takes into account the shrinkage ratio and suitably mills an expanded post core (Fig 10). Once the milling has been completed the holding sprue is cut using a diamond disc and the resultant post core is kept for sintering in the sintering furnace as per that particular material manufacturers instructions. (Fig 11,12) Normally it is sintered at around 1500 C(Fig 13). The whole cycle lasts for about 7 – 8 hrs. Once the sintering is completed, the CAD/CAM zirconia is trimmed and finished if required (Fig 14). The custom made CAD CAM post is then cemented with glass ionomer cement. An impression of the prepared tooth and core is then sent to the lab to fabricate an all ceramic crown.

While restoring anterior teeth with all ceramic crowns an esthetic post system such as zirconia post fabricated using CAD/CAM technology is a viable option for providing the patient with good esthetics without sacrificing strength. The procedure of obtaining a CAD/CAM post is relatively simple if an accurate resin pattern is made. The disadvantage is that zirconia is difficult to grind and hence it is difficult to make adjustments. If major changes are to be made, it is desirable to remake the post.

References

Fig. 14 Finished CAD CAM post and core milled from zirconia block.

1. Goodacre CJ, Spolnik KJ: The prosthodontic management of endodontically treated teeth: a literature review. Part I. Success and failure data, treatment concepts. J Prosthodont 1994; 3:243-250.

2. Awad MA, Fabrication of a custom-made ceramic post and core using CAD-CAM technology. J Prosthet Dent. 2007 Aug;98(2):161-2.

3. Ai B. Streacker, and Marc Geissberger, The milled ceramic post and core: A functional and esthetic alternative, J Prosthet Dent 2007;98:486-487.

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TPDI • January 2010, Vol. 1, No. 1 •

13

Research Evaluation of the ef fect of wet ting agents on gypsum dies made on polyvinyl siloxane impression materials: An in-vitro study Introduction Lakshmikanth K. * Sridhar Shetty N. ** Chethan Hegde ** Manoj Shetty **

* Senior Lecturer, Department of Prosthodontics AECS Maruti Dental College and Research Centre, Bangalore ** Professor, A B Shetty Memorial Institiute of Dental Sciences e-mail: lakshmikanth22@yahoo.com

14

Polyvinyl siloxane impression material have the undesirable property of high surface tension leading to poor recording of details in moist conditions as well as increased risk of voids in dies prepared on them. These voids are often located in critical parts of cast or dies such as line angles, margins, pinholes and retentive grooves.

Wetting the surface of impressions by the die material is highly critical, since the advancing contact angle of water placed on the impression material is related to the number of bubbles or porosities that occur on the casts or dies poured from the material. 1 To overcome these problems associated with the hydrophobic nature of the poly-vinyl siloxane impression materials, the manufacturers have introduced hydrophilic variants by adding an intrinsic surfactant or a wetting agent into the product, which is a surface active substance that reduces the surface tension of a liquid to promote wetting or adhesion.2 Although, hydrophilic polyvinyl siloxane containing a surfactant, has good wetting properties, studies have shown that the hydrophilic impression materials are less dimensionally accurate than the hydrophobic polyvinyl siloxane. The topical surfactants or wetting agents used on the hydrophobic poly-vinyl siloxane materials were more effective than intrinsic surfactants or wetting agents used within the hydrophilic materials. Further more dies poured from hydrophilic impressions appeared to have weaker surfaces than did those TPDI • January 2010, Vol. 1, No. 1 •

poured from the hydrophobic polyvinyl siloxane impressions.3 Objective of the study was to evaluate the effect of topical surfactants or wetting agents on the surface of the gypsum dies made on the hydrophobic monophase and hydrophilic monophase polyvinyl siloxane impressions.

Methodology Master model A metal master model with three fixed partial denture abutments measuring diameters of 8mm at the base, 7mm at the occlusal aspect and the occluso-gingival height of 10mm were fabricated. They were mounted 3mm apart on a base. On the occlusal surfaces of all the three abutments two perpendicular grooves of 0.3mm depth were made which intersected each other exactly at the center, and divided it into four equal halves (fig 1). A metallic perforated tray was fabricated, which could be placed precisely on the platform of the master model and it provided 3mm spacing.

Impression Ten impressions of metal master model were made using hydrophobic monophase polyvinyl siloxane material (President, Coltene) and another ten impressions were made using hydrophilic monophase polyvinyl siloxane impression material (Aquasil, Dentsply).

Dies All the twenty impressions made were stored at room temperature for one hour before pouring with type-IV gypsum (Die

Evaluation of the ef fect of wetting agents on gypsum dies made on poly vinyl siloxane impression materials: An in-vitro study

A Fig. 1 Diagrammatic Representation of the Master Metal Model

Fig. 4 Impression made using hydrophobic monophase polyvinyl siloxane.

B

C

Fig. 2 Master metal model

Fig. 3 Perforated tray

Fig. 5 Impression made using hydrophilic monophase poly vinyl siloxane.

Fig. 6 Stereomicroscope ( Carl Zeiss)

Graph : Comparison between number of voids on hydrophobic monophase polyvinyl siloxane impressions and hydrophilic monophase polyvinyl siloxane impressions.

Stone, Kalrock, Kalabhai.), The mixed material was loaded in a 5ml syringe and was injected over the impression. 1ml of gypsum was injected into each impression at a uniform rate of 30 seconds and vibrated on a low speed.

Group -1 Ten impressions were made using hydrophobic monophase polyvinyl siloxane impression material (President, Coltene), and each impression was poured with the type IV gypsum for three times. The first mix was poured without application of any topical wetting agent on the impression. The mix was allowed to set for one hour without any disturbance and die obtained was grouped as I a. After the first die was removed, the impression was thoroughly cleaned and dried and Smoothex topical wetting agent was applied on the impression and was allowed to dry for 5min. The second mix was poured and the die obtained was grouped as I b. After the removal of the second die the impression was again, thoroughly cleaned and Kerr (Sybron) topical wetting agent was applied. After 5minutes, third mix was poured and the die obtained was grouped as I c.

Group - 2 Ten impressions were made using hydrophilic monophase polyvinyl siloxane impression material (Aquasil, Dentsply), and each impression was poured with the type IV gypsum three times as described in group I. Abutments on all the sixty dies (samples) obtained were marked as A, B, and C corresponding to the abutments on the metal master model.

Evaluation of dies Each die was examined under the stereomicroscope under magnification of 10X. The number of voids in each of the four halves of the entire abutment were counted without considering the size of the voids, and any incomplete corners seen were considered as the voids.

Results Table I shows the comparison of the number of voids found on the dies. The mean number of voids found, on dies poured without application of topical wetting agent was 26.1 ± 7.68, on dies poured after

TPDI • January 2010, Vol. 1, No. 1 •

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Lakshmikanth K.

Table I Comparison of the no. of voids found on type IV gypsum dies, poured on hydrophobic monophase poly vinyl siloxane impressions without topical wetting agent, after application of the Smoothex topical wetting agent and after application of the Kerr topical wetting agent.

Group

N

Mean

Std.deviation

I-a

10

26.1000

7.68042

l-b

10

3.5000

1.17851

I-c

10

8.9000

2.46982

H

P

25.95

0.001

Table II Comparison of the no. of voids found on type IV gypsum dies, made on hydrophilic monophase poly vinyl siloxane impressions without topical wetting agent, after the application of Smoothex topical wetting agent and after the application of the Kerr topical wetting agent.

Group

N

Mean

Std.deviation

Il-a

10

24.0000

5.65685

Il-b

10

3.2000

1.47573

II-c

10

11.0000

2.44949

H

P

25.86

0.001

N= NO. OF SAMPLES H= KRUSKAL WALLIS TEST

application of Smoothex topical wetting agent was 3.5 ± 1.17 and on dies poured after application of Kerr topical wetting agent was 8.9 ± 2.46. The difference in the mean number of voids between these three groups was found to be statistically significant (p=0.001).

Comparison was made between the number of voids found on the dies poured on hydrophilic monophase polyvinyl siloxane impressions and given in table II. The mean number of voids found, on dies poured without application of any topical wetting agent was 24 ± 5.656, on dies poured after the application of Smoothex topical wetting agent was 3.2 ± 1.475) and on dies poured after the application of Kerr topical wetting agent was 11 ± 2.44. The difference in the mean number of voids between these three groups was found to be statistically very highly significant (p=0.001).

Discussion Least number of voids found among the dies poured on hydrophobic impressions without application of any topical wetting agent was 19 where as the maximum was 44 and mean was 26.1 with the standard deviation of 7.680. Dies poured on hydrophobic impression after application of Smoothex topical wetting 16

agent showed 1 as the least, 5 as the maximum number of voids and mean was 3.5 with the standard deviation of 1.178. Dies poured on hydrophobic impression after application of Kerr topical wetting agent showed least of 6 and the maximum of 14 numbers of voids the mean being 8.9000 and the standard deviation of 2.469.

The difference between these three groups was found to be statistically very highly significant (p=0.001). From this analysis it is evident that, the dies poured after application of topical wetting agents reduced the number of voids when compared to the dies poured without the application of any topical wetting agents.

This observation was comparable with the observations made by P. Brett Robinson, Stephen M. Dunne and Brain J. Millar and also by Jeffrey T, Susan J, Michael L, Manville G, Herbert T. Table II compares the number of voids on the dies obtained from hydrophilic monophase polyvinyl siloxane impressions without application of any topical wetting agents (group II a), with those of dies obtained after the application of the Smoothex topical wetting agent (group II b), and the dies obtained after the application of the Kerr topical wetting agent (group II c).

The number of voids on the dies obtained from

TPDI • January 2010, Vol. 1, No. 1 •

Evaluation of the ef fect of wetting agents on gypsum dies made on poly vinyl siloxane impression materials: An in-vitro study

hydrophilic impressions without application of any topical wetting agent ranged from a minimum of 16 to maximum of 33 with an average of 24 + 5.65.

The number of voids on the dies obtained from hydrophilic impressions after application of Smoothex topical wetting agent ranged from a minimum of 1 to maximum of 5 with an average of 3.2 + 1.47.

The number of voids on the dies obtained from hydrophilic impressions after application of Kerr topical wetting agent ranged from a minimum of 8 to maximum of 15 with an average of 11 + 2.44. The difference between these three groups was found to be statistically very highly significant (p=0.001). From the above findings it is evident that even though the hydrophilic polyvinyl siloxane incorporated intrinsic wetting agent, the dies poured on them without application of any topical wetting agent showed more number of voids when compared to the dies poured after the application of topical wetting agents.

Conclusions

The dies poured without application of topical wetting agent on hydrophilic monophase polyvinyl siloxane impressions showed marginally less number of voids when compared to the hydrophobic monophase polyvinyl siloxane impressions.

The dies poured on the hydrophilic and

hydrophobic monophase polyvinyl siloxane impressions after the application of Smoothex or Kerr topical wetting agent showed significantly less number of voids when compared to the dies poured without application of topical wetting agents.

Among Smoothex and Kerr topical wetting agents used in this study, the dies poured after the application of the Smoothex topical wetting agent showed significantly less number of voids than compared to the dies poured after the application of Kerr topical wetting agent.

It can be concluded that, before pouring die or cast on hydrophobic or hydrophilic monophase polyvinyl siloxane impression a topical surfactant could be applied to reduce the number of voids that might form on the die or cast, which in turn enhances the accuracy of prosthesis fabricated.

References 1. D H.Prattern, R Craig. Wettability of a hydrophilic addition silicone impression material J Prosthet Dent 1986;61:197-202.

2. P. Brett Robinson, Stephen M. Dunne and Brain J. Millar. An in-vitro study of a surface wetting agent for addition reaction silicone impressions. J Prosthet Dent 1994;71:390-3.

3. Panichuttra, Rose, Charles, Carlos, and Keith. Hydrophilic poly vinyl siloxane impression material. Dimensional accuracy, wettability and effect on gypsum hardness. Int J Prosthodont 1991;4:240-248.

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17

Education Good Teacher

I Chandrasekharan Nair K.*

* Professor and Head of the Depar tment of Prosthodontics, AECS Maaruti College of Dental Sciences and Research Centre, Bangalore e-mail: chandrasekharannair.drk@gmail.com

18

n ancient India teacher was known as Guru. The term guru has become very fashionable in modern times and which carries the tag of an expert. The word ‘Guru’ is derived from the Sanskrit language and has a deep spiritual meaning. Its two syllables Gu and Ru stand for the following: Gukaaro Gunaatheetham, Rukaro Rupavarjitah Gukaaro Andhakarascha, Rukaro Thannivarah Gu stands for gunatheetha (one who transcends the three gunassatwa, rajas and tamas) and Ru for rupavarjitah( one who is formless).

Also Gu means darkness; the darkness of ignorance. Ru means to remove. Therefore Guru is one who dispels the darkness of ignorance. In other words Guru represents the radiance of spiritual knowledge that dispels the spiritual ignorance.

Teacher is also known as Aacharya.

Aacharya is the one who practises and teaches the same to others.

Aacharya is the one who demonstrates through practice. In the modern context acharya is a role model who does serious thinking and research.

There are a few differences in the perceptions of modern and ancient teachers: The modern teacher considers teaching as a profession and teaches only for a specific period of time whereas the ancient teacher had no time limit.

While the modern teacher teaches through words, the ancient counterpart taught through words and beyond words. Modern teacher has no concern for students’ personal life on the contrary the ancient teacher looked after the student in every facet of life. Modern teaching TPDI • January 2010, Vol. 1, No. 1 •

is compartmentalized whereas ancient teaching encompassed everything.

The scriptures tell that all knowledge is within us. But there is a thin film of ignorance covering the knowledge. The teacher does not teach, but removes the thin layer and brings out the knowledge. Perhaps this is what is meant by guidance from the teacher. Good teachers are excellent facilitators who make the students learn. The process of learning is always carried out by the student. Teachers do not teach but make the student learn by unveiling the knowledge within.

The teacher in Bharat always stood on a very high pedestal. The process of teaching and learning was treated as a sacred action and not a commercial activity. Knowledge stood head and shoulders above every other kind of wealth. Scholars were respected much more than those who were rich in money and power.

Roles of a teacher 1. Teachers are to be good Good teachers are really passionate about teaching and they strive hard to improve their methods. Their focus is always on the student and helps the student who really wants to succeed. Good teacher should be sincere and sincerity cannot be faked. The achievements of the student should make the teacher proud even if it is not recognized by the student.

Teacher should be broad minded to acknowledge the competence of the student. At no point of time, jealousy should creep into the mind of the teacher on meeting with the excellence of the student. An

Go od Teacher

excellent student is stimulated to explore more by a mediocre teacher than an excellent teacher who would provide ready answers. In fact teachers are to be good otherwise they cease to be teachers.

2. Teacher should be knowledgeable Teacher should know what the students are supposed to learn at the end the course. For that there is no doubt, the teacher should be thorough with the subject he teaches. Teachers are tempted to overload the student with knowledge content which will not be assimilated by the student. So teacher should take a decision on the essentials which student should learn. The essentials are to be repeated many times during the instructional period. Training or repeated performance makes the student proficient and proficiency becomes a habit. This habit changes the attitude of the student. Good teachers can make lasting impressions on their students not by the volume of knowledge the teacher possesses, but by the number of essentials he could transcend thereby creating a great attitudinal transformation.

3. Good teachers are creative Creative teachers do not teach but they make their students learn. For them the normal parameters will not serve the purpose. The lessons they intend to teach will be presented in different ways that the student will not know how they learned them. Creative teachers require more academic freedom and they take risks in their methods. It is termed as a risk because every time success cannot be expected when a new methodology is implemented. If there is no chance of failure, then success is meaningless. Same subject matter cannot be presented to the students in the same way year after year. Old techniques make a creative teacher threatened and he thinks of fresh ways of making the student learn.

The story how fish stayed fresh when threatened by sharks is one of the finest examples: The Japanese have always loved fresh fish but the waters close to Japan did not have much fish. To feed the population the fishing boats got bigger and went farther than ever. The farther the fishermen went, the longer it took them to bring in the fish. If the return trip took more than a few days, the fish were not fresh and the Japanese did not like the taste. To solve this problem fishing companies installed freezers on their boats. Unfortunately the consumers could taste the difference between fresh and frozen fish. So fishing companies installed fish tanks in the ship. After a little thrashing around, they stopped moving. They were dull, tired but live. Japanese could still taste the difference. Finally they hit upon an idea which could make the fish agile. A small shark was added to each tank. The shark did eat a few fish but the rest of the fish were challenged and kept on the move. Japanese consumer got the freshest possible fish. The creative teacher feels challenged by old techniques making him seek new ideas and projects as fresh as ever.

4. Challenging the student Good teachers try to keep their students off balance, forcing them to step into challenges that they are not at all sure they can handle. Good teachers push and challenge their students, jerking them into places where they feel uncomfortable, where they don’t know enough, where they cannot slide by on past knowledge or techniques.

Good teachers, as soon as their students have mastered something, push their best students well past the edge of their comfort zone, striving to make them uncomfortable, to challenge their confidence so they can earn a new confidence. Challenging situations make the student explore into newer areas culminating in great success. The student feels that the teacher is with him and his confidence level increases. The teacher feels proud when the student achieves but when he fails, the teacher encourages him and gives a nice lesson on how to face failure.

5. The role model Role models are people who have qualities we would like to have and are in positions we would like to reach. Role models have been shown as a way to inculcate professional values and attitudes in students and in young medical professionals. The teacher as a clinician should model or exemplify what should be learned. Students learn not just from what their teachers say but from what they do in their clinical practice and the knowledge, skills and attitudes they exhibit. Teachers serve as role models not only when they teach students while they perform their duties as doctors, but also when they fulfill their role as teachers in the classroom, whether it is in the lecture theatre or the small discussion or tutorial group. The good teacher who is also a doctor can describe to a class of students, his approach to the clinical problem, discuss in a way that captures the importance of the subject and explain the choices available. The teacher has the unique opportunity to share some of the magic of the subject with the students.

Students and young doctors consider enthusiasm, compassion, openness, integrity, and good relationships with patients as attributes they seek in their role models.

They are also drawn to senior professionals who embody responsibility and status. When some senior doctors show poor attitudes and unethical behaviour, it causes confusion, distress and anger in young doctors and students under their supervision. By no means all doctors with teaching responsibilities have the attributes that students and young doctors seek in their role models.

However it should be realized that role modeling is not the only method to impart professional values and attitudes.

6. The information provider A traditional responsibility of the teacher is to pass on to students the information, knowledge and understanding in a topic appropriate at the stage of their

TPDI • January 2010, Vol. 1, No. 1 •

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K.Chandrasekharan Nair

studies. This leads to the traditional role of the teacher as one of provider of information generally in the lecture context. The lecture remains as one of the most widely used instructional methods. It can be a cost-effective method of providing new information not found in standard texts, of relating the information to the curriculum and context of medical practice and of providing the lecturer’s personal overview or structure of the field of knowledge for the student.

The clinical teacher passes information in the clinical setting, either in the hospital or in the community and the information is directly relevant to the practice of medicine. Good clinical teachers can share with the student their thoughts as a reflective practitioner, helping to illuminate the process of clinical decision making.

7. The facilitator Facilitator helps to bring about an outcome (as learning, productivity, or communication) by providing indirect or unobtrusive assistance, guidance or supervision. Presently learning has become more student centered. Hence the fundamental shift to the role of facilitator. A good teacher will be a good facilitator. No longer is the teacher seen predominantly as a dispenser of information or walking tape recorder, but rather as a facilitator or manager of the students’ learning. The introduction of problem-based learning with a consequent fundamental change in the student-teacher relationship has highlighted this change in the role of the teacher from one of information provider to one of facilitator. However teacher should not feel that the facilitator role is very passive. Rather it is an active role.

The student might feel that the teacher simply observes and the effort is put in by him. The teacher starts teaching a new subject and gives some problem to solve. Some information is given by the teacher as an introduction and later provides a list of resources where the student can find the solution to the problem. Teacher allows time but the job is time bound. The student is emboldened by this process but he may not be aware that the teacher had to go through many books and journals to provide the list of resources. That is the reason, it was stated that the facilitators job not passive but active.

8. The mentor Mentor was described by Homer as the “wise and trusted counselor”. In modern times, the concept of mentoring has found application in virtually every forum of learning. In academics, mentor is often used synonymously with faculty adviser. A fundamental difference between mentoring and advising is more than advising; mentoring is a personal, as well as, professional relationship. As mentor is someone who takes special interest in helping another person develop into a successful professional. The role of mentor is a further 20

role for the teacher. Mentorship is less about reviewing the students’ performance in a subject or an examination and more about a wider view of issues relating to the student. In short career development based on value system is possible only through mentoring.

9. The teacher should evaluate and assess the student Assessment of the student’s competence is one of the most important tasks facing the teacher. Through conventional or unconventional methods, a teacher evaluates the students on their achievements about which the teacher clearly states at the beginning of the course.

Examining does represent a distinct and potentially separate role for the teacher. A student is evaluated throughout the course with a component of feed back is usually known as formative evaluation. At the end of a term, the student is evaluated by a formal process of examination which is known as summative evaluation.

Teacher should gain expertise on the different components of evaluation process. Setting a question either for a written examination or for a viva, involves a meticulous process in which all the teachers may not be good even though they are good in making the students learn. It is better to learn the evaluation process from senior teachers or through training programmes all good teachers should try to be good evaluators or assessors of students learning.

The teacher has a responsibility not only to plan and implement educational programmes and to assess the students’ learning, but also to assess the course and curriculum delivered. Monitoring and evaluating the effectiveness of the teaching of courses and curricula is now recognised as an integral part of the educational process.

While assessing the teaching process and curriculum, teachers should subject themselves for a monitoring of their own performance also. Quality teaching is closely related to personal development which is possible only by a self assessment process.

10. The planner A teacher should be able to contribute towards planning of the curriculum. For this purpose teacher should get himself trained on the basics of medical education technology. He should also be aware of the health needs of the country and the health policy adopted by the Government. With an improved awareness of these components, a teacher will be able to contribute towards the planning process. Universities and institutions usually have bodies containing experts and teachers for this purpose. Curriculum planning presents a significant challenge for the teacher and both time and expertise are required if the job has to be

TPDI • January 2010, Vol. 1, No. 1 •

Go od Teacher

undertaken properly. In an institutional and departmental level, the teacher should plan the course without losing its relevance and at the same keenly verifying for its capability to bring in observable and measurable changes in the students.

11. Be an author or resource developer There is an increased need for learning resource materials in the modern educational system. New technologies have greatly expanded the formats of learning materials which are easily accessible to the students. Learning materials make the introduction to a subject much easier which otherwise would be tough.

The student finds the study interesting because of greater understanding and he feels more responsibility. The role of the teacher as resource creator offers exciting possibilities. Teacher should be able to produce books on his subject of teaching or produce notes (study guides) adapted from standard text books which are already available. Study guides suitably prepared in electronic or print form can serve as the students’ personal tutor, available 24 hours a day and assist the students with their learning. Study guides tell the student what they should learn - the expected learning outcomes for the course, how they might acquire the competencies necessary - the learning opportunities available, and whether they have learned it - the students assessing their own competence.

12. Good communicator and presenter A teacher of the health profession should primarily be a good doctor capable of identifying patients’ problems accurately. Their patients adjust better psychologically and are more satisfied with their care.

Doctors with good communication skills have greater job satisfaction and less work stress. The basic skills involve speaking in simple fashion and listening greatly.

These skills will make a teacher communicate well with the students. This will improve the teacher student relationship and students will feel that the teacher is approachable.

Teacher should be a good presenter too. To be a good presenter, basics of public speaking must be learned either by observation, reading or by training.

Present day teacher should acquire skills such as making a power point presentation, photography, operational knowledge of computers, LCD projectors, over head projectors, preparation of word documents, photocopying and the use of white and black boards.

Internet has become an essential tool for the teacher in accessing and updating knowledge.

Students say No

In a study conducted among junior dentistry students on the qualities of a teacher, they have specifically said no to certain behavior which is listed below: -do not be rude -do not be partial -should not be impatient -should not be very lenient -should not give loads of work as assignment -teacher should not be diffident on what he teaches -should not involve personal problems with teaching Many who reads this might think, is it possible to achieve all the good qualities and to avoid the bad qualities. Let us be positive and strive hard to become a teacher in its true spirit. If you are true to the elements, have commonsense, adequate knowledge, interest in teaching and talent, there is no way you cannot be a good teacher

Thus spake the wise people The mediocre teacher tells.

The good teacher explains.

The superior teacher demonstrates.

The great teacher inspires.

William Arthur Ward Give me a fish, I eat for a day. Teach me to fish, I eat for a life time. This must be the philosophy of a good teacher.

Anonymous A teacher who is attempting to teach without inspiring the pupil with a desire to learn is hammering on cold iron Horace Mann Good teachers are costly, but bad teachers cost more.

Bob Talbert The best teachers teach from the heart not from the book Anonymous

Bibliography Ronald J M: What makes a good teacher; Academic medicine 76:809-10, 2001 Warrier B S: The ideal teacher; The Hindu, Education plus, September 2007 Earnest O M: The teacher and learning;http://Honolulu.hawaii.edu Chris Morgan: Learning matters at lingnan, w w w.ln.edu.hk Moragano S M, Qualities of an exemplary dental educator, Editorial, Soudi Dental Journal, 1993 w w w.spiritualresearchfoundation.org

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Review A review on the design and sur face characteristics of modern dental implants Jayakar Shetty * Anupama M.S. ** Srividya S. *** Chandrasekharan Nair K. ****

*Professor and head of the Department of Implantology **PG Student, ***Senior lecturer, ****Professor and Head of the Department of Prosthodontics AECS Maaruti College of dental Sciences and Research centre, Bangalore e-mail: shett yjayakar@gmail.com

22

I

mplants have become a popular treatment method in today’s dental practice. The first twenty years focused mainly on gaining acceptance for the treatment method.

With more and more design variations and surface characterizations, dental implants have become more popular in dentistry. Endosteal implant systems are placed into the alveolar bone of the mandible or maxilla and are used to support a prosthesis. A dental implant designed to replace a single tooth is composed of three parts: the titanium implant that osseointegrates with the bone; the abutment, which fits on the implant and protrudes through gingiva; and the crown, which is fitted onto the abutment for a natural appearance.

They can be either of one of the two basic shapes viz. root form or cylinder form. A root-form implant manufactured with threads similar to a hardware screw. The sides may be parallel or tapered. The threaded surface provides for retention during initial bone fixation as well as an increased surface area for osseointegration. Threaded implants reduce shear force at the boneimplant interface. Cylinder form is an endosteal root-form implant featuring parallel-sided, nonthreaded walls. Cylindrical implants are usually pushed or tapped into a prepared bone site and rely on a variety of manufactured coatings to support osseointegration. 1 An antirotational feature in the implant fixture is either included in the platform when it is called external hex, or can extend in to the implant body called an internal hex. The antirotational feature can be in the form of a hexagon, octagon, morse taper or cone screw, internal TPDI • January 2010, Vol. 1, No. 1 •

grooves or cam tube and pin slots. 2 Even though dental implants have a success rate of upto 90% for five years, the remaining 10 % of failure is still a big number. This failure of dental implants is mainly observed in soft bone. In order to achieve a predictable outcome even in poor density bone the surface topography of dental implants have been enhanced in the recent past. It has been observed that the microscopic and macroscopic topography of dental implants affect the primary initial stability of the dental implants.

Hence manufacturers have come out with an array of different screw thread profiles and surface coatings in order to create a stable implant to bone contact.

Design principles that need to be considered are: 1) The implant design should provide good initial stability and minimize the waiting-period required for loading the implant.

2) Incorporate design factors, that would diminish the effect of shear forces on the interface (such as surface roughness related and thread features) so that marginal bone is preserved.

3) Design features that may stimulate bone formation, and/ or facilitate bone healing. 3 Threads have been incorporated into implants to improve initial stability, enlarge implant surface area, and distribute stress favorably. Kohn et al demonstrated the presence of a bone-bridge from the depth of one thread to another, when the implants were laterally loaded.

The original Brånemark screw (introduced in 1965) had a V-shaped

A review on the design and Surface characteristics of modern dental implants

threaded pattern. While some manufacturers modified the basic V thread, others used a reverse buttress with a different thread pitch for better load distribution.

Thread patterns in dental implants currently range from microthreads near the neck of the implant (Astra Tech, Lexington, MA) to broad macrothreads on the mid-body (Biohorizons, Birmingham, AL; Steri-Oss, Nobel Biocare) and a variety of altered pitch threads to induce self-tapping and bone compression (Implant Innovations, Palm Beach Gardens, FL; Nobel Biocare).

Implant neck (crest module) : The highest bone stresses have been reported to be concentrated in the cortical bone in the region of the implant neck as demonstrated in Finite Element Analysis (FEA) of loaded implants with or without superstructure. The implant neck design is one of the areas of development. Micro-textured and the macro-textured surfaces were explored. These designs mainly aimed to enhance the stability of interface for both soft and hard tissue and minimise the marginal bone reduction in the first year of implantation Tarnow et al have shown that the soft tissue height adjacent to the implant depends upon the marginal bone height. To maintain the soft tissue height adjacent to the implant especially in the esthetic zone, the crest module has to be smooth. If it is rough then the soft tissue will shy away from the implant surface. Apart from hard and soft tissue grafting, distraction osteogenesis, implant fixture design also have been modified to achieve better esthetic outcome. There are three basic types of a turned neck (TN) Avana implantsystem, Osstem co., Ltd., Seoul, Korea)implant, micro-threaded (MT) neck implant Oneplant, Warantec, Seoul, Korea and micro-grooved (MG) neck implant (Laser-lok, Bio-lok international Inc.Deerfield Beach. USA). The MT and MG implants, especially MG implants had advantageous tissue response in comparison to the turned neck implants.4 Platform switching : In many two part systems the Implant abutment interface (IAI) can give rise to an area of local inflamation causing bone resorption.

A biological width of 2-3mm is needed above the bone inorder to establish a soft tissue barrier. It has been found that the bioligical width need not be a vertical dimension but can have a horizontal component, platform switching provides this horizontal distance and so preserves the crestal bone.

Histologic and radiographic observations suggest that a biologic dimension of hard and soft tissues exists around dental implants and extends apically from the implant-abutment interface. The vertical repositioning of crestal bone and the subsequent soft tissue attachment to the implant that occurs when an implant is uncovered and exposed to the oral environment establishes a biological width in an implant. Traditionally a matchingdiameter restorative components are attached.

Historically, two-piece dental implant systems have been restored with prosthetic components that locate the interface between the implant and the attached component element at the outer edge of the implant platform. The concept of platform switching refers to restoration of wide diameter implant with narrow diameter abutment. Long-term radiographic follow-up of these “platform-switched” restored wide-diameter dental implants has demonstrated a smaller than expected vertical change in the crestal bone height around these implants than is typically observed around implants restored conventionally with prosthetic components of matching diameters.5 Surface treatments of implants : Currently the trend of clinical implant surface modifications is shifting towards changes in surface chemistry rather than machined surface.

The various surface modifications presently available are : turned surface, Sand blasted surface,acid etched surface,Titanium plasma spray, Sand blasted- surface etching, Hydroxyapatite coating, Anodized surfaces, Laser induced surface roughening, Ion implantation, Glow discharge, Electrochemically oxidized TiUnite implants (Nobel Biocare), Fluoride treated osseospeed implants (Astra Tech), Nacl treated hydrophillic sand blasted large grit acid etched implants (Straumann)The titanium porous oxide implant surface serves as an effective carrier for BMP- 7. This has a clinically significant potential to stimulate local bone formation. Bone formation will occur due to induction as well as interaction of growth factors. Osseotite Implant Combined with a nanometer-scale discrete crystalline deposition of calcium phosphate (CaP) creates a more complex surface topography.

Implants have come to stay here changing the entire profile of Prosthodontic treatment. The first decade of 21st century has really stabilized the implant design and surface. But definitely there will be exciting changes that will happen in the next decade.

References 1. Carl Misch, Contemporary Implant dentistry, 3rd edition, Mosby publications, 602-603 2. Rudi C. Van Staden, Hong Guan, Yew-Chaye Loo, Newell W. Johnson & Meredith Nell, Comparative analysis of internal and ex ternalhex crown connection systems - a finite element study, J. Biomedical Science and Engineering, 2008; (1): 1014 3. Linish Vidyasagar, Peteris Apse,. Dental Implant Design and Biological Effects on Bone-Implant Interface, Stomatologija, Baltic Dental and Ma xillofacial Journal, 2004; 6:51-4 4. Hanna Eun Kyong Bae, Moon-Kyu Chung1In-Ho Cha DongHoo Han,Marginal tissue response to different implant neck design, J Korean Acad Prosthodont 2008; (46): 6, 602 – 09 5. Lazzara, Porter Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels, Int J Periodontics Restorative Dent. 2006;26(1):9-17

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In Shor t 1) Kious A.R et al, Film thickness of recently introduced luting cements, J Prosthet Dent 2009; 101:189-192 The luting cements tested, two resin modified glass ionomer cements (Fuji CEM and RelyX), two composite resins (Panavia 21 and Rely X ARC) and two self adhesive resins (Maxcem and Rely X unicem) met the ISO standard of 25µm maximum film thickness for upto 2 minutes after mixing. At 2 minutes the film thickness ranged between 8.9 µm to 25.4µm. At 3 minutes after mixing the film thickness increased to 53.6µm. The quantity of cement was not specified in the study. Its influence on film thickness has to be explored. The load used was 150 N. 2) Hansen et al, Making multiple predictable single unit provisional restorations using an indirect technique, J Prosthet Dent 2009; 102:260-63 This article describes a method to fabricate single provisional restorations for multiple preparations using an indirect technique. Wax up is done for the teeth before tooth preparation and a cast poured for the same. A vacuum formed matrix is adapted on the cast and an acrylic splint is placed on it to prevent the distortion of the vacuum formed matrix. The interproximal separation of teeth is achieved with the help of a matrix band placed buccolingually touching the surface of the cast.

3) Shibayama et al, Effect of flasking and polymerization techniques on tooth movement in complete denture processing, J Prosthodont; 18(2009):259-64 Here conventional gypsum flasking and water bath polymerization was compared with flasking using a silicone cap and microwave polymerization. It was seen that the silicone cap and microwave polymerization showed lesser tooth movement during complete denture processing.

4)WonSuk et al, Incisive papilla line as a guide to predict maxillary anterior tooth display, J Prosthet Dent 2009; 102:194-96 This article described a simple and accurate procedure for marking the vertical level of the incisive papilla on the occlusion rim of determine its distance from the resting lip and estimate the maxillary anterior tooth display required for a patient.

5) Choi et al, An alternative technique for fabrication of an occlusal device, J Prosthodont 2008; 17:423-426 This article gave a technique of fabricating an occlusal device without flasking and removing the cast from the articulator by using a silicone putty index. The wax pattern was made, a silicone putty index covering the maxillary teeth to the occlusal surface of the device was made and autopolymerizing acrylic resin was injected into access holes.

6) Sari and Usumez, Restoring function and esthetics in a patient with amelogenesis imperfecta: A clinical report, J Prosthet Dent 2003; 90:522-5 This clinical report describes restoration of amelogenesis imperfecta affected teeth with laminate veneers and metal ceramic crowns.

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7) Daniela Maffei et al, Effects of thermocycling on the bond strengths of three permanent soft denture liners, J Prosthodont 17(2008):550-54 The clinically accepted level of bond strength of soft denture liners to the denture base is 0.44 MPa. The bond strength of acrylic autopolymerizing resin denture liner to denture base was found to be 1.19 MPa before thermocycling and 3.32 MPa after thermocycling. Hence it was concluded that the bond strength increased after thermocycling.

8) Valle MC, Accuracy of friction style and spring style mechanical torque limiting devices for dental implants. J Prosthet Dent 2008; 100:86-92 Mechanical torque limiting devices that use spring style components were found to be significantly more accurate than the friction style components in achieving their target torque values. The torque applied on the prosthetic screw ranged between 20N cm to 35 N cm.

9) Ohlmann et al, Fracture load values of all ceramic cantilevered FPD’s with different framework designs, Int J Prosthodontics 2009; 22:49-52 All ceramic cantilevered fixed partial dentures made of zirconia framework were found to fracture below the masticatory load (700 N) between 346-548 N. Hence they were not recommended to replace molars.

10) Gozalo Diaz D, Estimating the colour of maxillary central incisors based on the age and gender, J Prosthet Dent 2008; 100:93-8 As age advances the central incisors were found to become darker, more reddish and more yellowish in colour.

When compared to men, women have lighter and less yellow central incisors.

11) D Brown, Resilient soft liners and tissue conditioners.

Br Dent J 1988; 164:357-61 Resilent soft liners were found to absorb more energy as compared to the hard acrylic base when subjected to stress. Addition of plasticizers reduced the glass transition temperature of polymethyl methacylate (105 0 C) and polybutylmethacrylate (1350C). Beyond this temperature the liners remains in a state of softness.

12) Conserva E et al, The use of a masticatory robot to analyze the shock absorption capacity of different restorative materials for prosthetic implants: A preliminary report, Int J Prosthodontics 2009; 22:53-5 Composite crowns are able to absorb shock and transmit less forces to the peri implant bone when compared to ceramic crowns when subjected to the same occlusal load. The load transmitted was 59.784 kg for Empress II ceramic and 22.429 kg for Signum composite.

Compiled by :

Manikya Arabolu, Navpreet Chhatwal, Sushma, Sadhvi K V, Gunjan Singh, Preeti Kalia, Aswini Khandare

TPDI • January 2010, Vol. 1, No. 1 •