Rastogi+Abhishek

i

RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES, BANGALORE,

KARNATAKA.

“COMPARISON OF THE CLINICAL EVALUATION OF THE MARGINAL

ACCURACY OF THE CAST RESTORATION WITH

STEREOMICROSCOPY”

Dissertation submitted in partial fulfillment of the

requirement for the degree of

MASTER OF DENTAL SURGERY

IN PROSTHODONTICS, CROWN & BRIDGE

APRIL – 2009 Dr. ABHISHEK RASTOGI

ii

DEPARTMENT OF PROSTHODONTICS, CROWN & BRIDGE

P.M. NADAGOUDA MEMORIAL DENTAL COLLEGE & HOSPITAL,

BAGALKOT – 587 101, KARNATAKA.

“COMPARISON OF THE CLINICAL EVALUATION OF THE MARGINAL

ACCURACY OF THE CAST RESTORATION WITH

STEREOMICROSCOPY”

By

DR. ABHISHEK RASTOGI

Dissertation Submitted to the

Rajiv Gandhi University of Health Sciences, Bangalore, Karnataka

In partial fulfillment of the requirements for the degree of

MASTER OF DENTAL SURGERY

In

PROSTHODONTICS

Under the Guidance of

Dr. VIKAS KAMBLE

DEPARTMENT Of PROSTHODONTICS, CROWN & BRIDGE P. M. N. M. DENTAL COLLEGE AND HOSPITAL

Year: 2009

RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,

iii

BANGALORE

RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,

BANGALORE

DECLARATION BY THE CANDIDATE

I here by declare that this dissertation entitled “Comparison of the clinical

evaluation of the marginal accuracy of the cast restoration with

stereomicroscopy” is a bonafide and genuine research work carried out by me under

the guidance of Dr Vikas Kamble M.D.S, Associate Professor, Department of

Prosthodontics, P.M.N.M Dental College & Hospital, Bagalkot.

Date: Signature of the Candidate

Place: Bagalkot Dr. Abhishek Rastogi

iv

CERTIFICATE BY THE GUIDE

This is to certify that the dissertation entitled “Comparison of the clinical evaluation

of the marginal accuracy of the cast restoration with stereomicroscopy” is a

bonafide research work done by Dr. Abhishek Rastogi in partial fulfillment of the

requirement for the degree of Master of Dental Surgery.

Date: Dr. Vikas Kamble M.D.S,

Place: Bagalkot Guide,

Associate Professor,

Department of Prosthodontics

P.M.N.M Dental College & Hospital,

Bagalkot 587101

v

ENDORSEMENT BY THE HEAD OF THE DEPARTMENT,

PRINCIPAL/ HEAD OF THE INSTITUTION

This is to certify that the dissertation entitled “Comparison of the clinical evaluation

of the marginal accuracy of the cast restoration with stereomicroscopy” is a bonafide

research work done by Dr. Abhishek Rastogi under the guidance of Dr.Vikas

Kamble M.D.S, Associate Professor, Department of Prosthodontics, P.M.N.M Dental

College & Hospital, Bagalkot.

Dr. VIKAS KAMBLE M.D.S Dr. SHRINIVAS S VANAKI M.D.S

Associate Professor and Head, Principal,

Department of Prosthodontics, P.M.N.M Dental College &

P.M.N.M Dental College & Hospital, Hospital,Bagalkot-587101

Bagalkot-587101 Date:

Place: Bagalkot

vi

COPY RIGHT

Declaration by the Candidate

I here by declare that Rajiv Gandhi University of Health Sciences, Karnataka

shall have rights to preserve, use and disseminate this dissertation in print or

electronic format for academic / research purpose.

Date:

Place: Bagalkot Dr. Abhishek Rastogi

© Rajiv Gandhi University of Health Sciences, Karnataka

vii

Dedicated

To

My Beloved Parents

Whose Countless Sacrifices Made My

Dreams A

Reality

““VVaakkrraattuunnddaa MMaahhaakkaayyaa SSuurryyaakkoottii SSaammaapprraabbhhaa,, NNiirrvviiggnnaamm KKuurruummeeddeevvaa SSaarrvvaakkaarryyeesshhuu SSaarrvvaaddaa””

viii

ACKNOWLEDGEMENT

This thesis represents the assistance and efforts of many individuals, the

contributions of whom I acknowledge and to whom I give my thanks.

The individual most responsible for the completion of this study is my guide

Dr.Vikas Kamble, Associate Professor and Head, Department of Prosthodontics,

P.M.N.M Dental College, Bagalkot. His tireless pursuit for academic excellence and

professional insight were a source of constant encouragement and inspiration. A

mere word of thanks is not sufficient to express his unflinching support, keen

surveillance, inestimable aid and continued inspiration during the preparation of

this dissertation. He is a person who has a rare combination of being a dedicated

professional and a caring human being. I will be indebted to him for his

overwhelming help and kindness.

It is with supreme sincerity and deep sense of appreciation that I thank my

esteemed teacher Dr. Raviraj G.Desai Associate Professor, Department of

Prosthodontics, P.M.N.M Dental college, Bagalkot. He has always given me

excellent guidance, encouragement and friendly help during the course of my entire

post graduation and under whose shade I comfortably grew up in department. His

inspiration and encouragement have molded me to present.

My heartfelt gratitude to Dr. (Mrs) Veena K. Subbarao former Professor,

and Head, Department of Prosthodontics, P.M.N.M Dental college, Bagalkot, a

teacher of inspiring genius and unstinting generosity for her overall guidance,

encouragement, and suggestions during the course of this study.

I would also like to thank Dr. Chandu G.S., former Associate Professor for

his valuable suggestions and assistance throughout my postgraduate course.

I would like to thank our staff members Dr. Kashinath Arabbi, Dr Reshma

Kulkarni and Dr Nagraj for their support and kindly help.

ix

I would like to express my thanks to our Principal Dr. Shrinivas S.

Vanaki, for his support and providing me with adequate facilities for my study.

Expressions are inadequate to convey my immense gratitude to Dr. S.S.

Vanaki, Dr. R. S. Puranik and Dr. Shivakumar for allowing me to

carry out stereomicroscopic evaluation as a part of my research work.

I also thank our honorable chairman Shri. V. C. Charantimath for

providing all the necessary facilities and an opportunity to carry out this study.

My ever encouraging and helping colleagues Dr. D R V Kumar, Dr. Sumit

Deshpande, Dr. Dayanand Huddar, Dr Piyush Tandon, Dr. Alok Sharma, Dr.

Nishant Rajwadha, Dr Suresh Nagral, Dr Amandeep Bhullar, Dr Pavan Kulkarni,

Dr Hitendra Yadav and Dr Suchitra S.R for their support, valuable criticism,

suggestions and unfailing companionship.

Among my friends Dr. Lakhmikant, Dr. Sudhakara and Dr Mangesh

Shenoy requires special thanks for helping me out during my study.

I owe sincere thanks to Mr. Abdul for his helping me to carry out my lab

procedures during my study.

I owe sincere thanks to Mr. S. B. Javali for his statistical help.

I would like to thank our librarian for his immense support and providing me

books and journals during my study.

I convey my deepest gratitude to all other staff members, my post graduate

colleagues for their help throughout this study.

My special thanks to my parents and all my family members for their unseen

sacrifices, constant advice, support and encouragement in every moment of my study.

Their cheerful encouragement, timely support and cooperation made me to do my

work better with my maximum enthusiasm.

Lastly I wish to thank all those who have directly or indirectly contributed

to the successful completion of this dissertation.

…… Dr. Abhishek

x

LIST OF ABBREVIATIONS USED

o µm – Microns

o SD – Standard Deviation

xi

ABSTRACT

Background and Objectives:

One of the most important criteria for the clinical success and longevity of cast

restorations is its marginal adaptation. Marginal discrepancies adversely affect local

periodontal tissue condition. There are several commonly used techniques to evaluate

the accuracy of marginal fit of cast restoration prior to clinical acceptance. These

include the use of dental explorer and Elastomeric disclosing materials.

Studies have reported 30 microns to be a clinically acceptable gap

discrepancy. However, there is limited information on sensitivity and specificity of

commonly practiced clinical evaluations in detecting a marginal discrepancy of this

magnitude. The indications for the use of die spacers in fabrication of cast restorations

are well documented in the literature. In this in vitro study, die spacer was

intentionally not used to create variations in casting fit for the purpose of the study.

The aim of this study was to assess the effect of preparation design on

marginal adaptation, as well as to assess sensitivity and specificity of clinical

evaluation (i.e. explorer and elastomeric disclosing material) of cast restoration

marginal adaptation when compared to stereomicroscopy.

Materials and method:

Three Ivorine molar teeth of different designs were prepared

Design A-A complete crown preparation with a buccal shoulder (1mm wide)

and bevel as remaining finish line.

Design B -A complete crown preparation with a chamfer finish line.

Design C-A three-quarter crown preparation with proximal boxes and beveled

finish line.

Elastomeric impressions of each tooth were made using individual custom-

fabricated trays. Eight individual dies were fabricated of each design. A total of 24

dies were prepared. Wax patterns were fabricated on the dies using type II inlay wax

and casted using a non precious gold alloy. The casting procedures were standardized

by investing immediately after waxing.

Each casting underwent examination with an explorer, disclosing media, and a

stereomicroscope. Twelve circumferential recordings were made of each casting,

xii

three on each buccal, lingual, mesial and distal surface, marked with a groove on

original ivorine teeth and highlighted using a fine indelible marker, for a total of 288

examination sites. A ranking of “fit” or “misfit” was given to each examination site

after assessment with explorer and disclosing media.

Stereomicroscopy at a value less than or equal to 30 microns measurements

was used as a gold standard to evaluate the significance of different designs on

marginal adaptation. Three sites for each buccal, lingual, mesial, and distal surface

were given an overall evaluation of fit or misfit.

A surface was raked fit where all 3 measurement points on a surface were less

than or equal to 30 microns using stereomicroscopy. If any of three measurement

points of a surface had a value of greater than 30 microns, that surface was ranked as

misfit.

Chi-square tests of independence and Kruskal-Wallis were used to evaluate the

effect of preparation design and compare the agreement between examination

methods for detection of marginal gap size of greater than or equal to 30 microns.

Sensitivity and specificity for explorer and disclosing media as compared to

stereomicroscope was calculated using statistical formula given by Park.

Results:

The preparation design did not significantly affect overall marginal adaptation.

Examination by explorer at 30µm revealed 39% sensitivity and 91% specificity.

The disclosing media had 10.06% sensitivity and 82% specificity at 30µm.

Conclusion:

Preparation designs examined in this study did not significantly affect the

marginal adaptation and accuracy of the castings.

Commonly used clinical evaluation techniques i.e explorer and elastomeric

disclosing media may be inadequate for assessments of marginal accuracy.

Explorer technique proved to be better aid in detection of marginal accuracy as

compared to elastomeric disclosing media.

For better evaluation of marginal accuracy of the cast restorations, the routine

use of a stereomicroscope in the laboratory is indicated which provides a superior

quality control prior to examination of restorations intraorally.

xiii

TABLE OF CONTENTS

Page No.

1. Introduction 1

2. Objective 5

3. Review of literature 6

4. Materials and method 22

5. Results 39

6. Discussion 54

7. Conclusion 58

8. Summary 59

9. Bibliography 61

10. Annexure 66

xiv

LIST OF TABLES

1. Readings of all three preparation designs using explorer. 42

2. Readings of all three preparation designs using elastomeric

disclosing media. 43

3. Readings of all three preparation designs using stereomicroscope. 44

4. Distribution of overall marginal adaptation of crowns by three

designs using explorer technique. 45


designs using elastomeric disclosing media. 46


designs using stereomicroscope. 47

7. Comparison of mean marginal openings of three designs in

Stereomicroscope by Kruskal Wallis Anova test. 48

8. Marginal accuracy findings on buccal, lingual, mesial, distal

surfaces of three preparation designs. 49

9. Percentage of 288 sites with inadequate marginal fit as detected

by explorer, elastomeric disclosing media and stereomicroscope. 50

10. Results of stereomicroscopic evaluation of 288 marginal gap sites

compared to explorer using stereomicroscope as gold standard. 51

11. Results of stereomicroscopic evaluation of 288 marginal gap sites

compared to elastomeric disclosing media using stereomicroscope as

gold standard. 51

12. Illustration 1 and 2 for calculation of sensitivity and specificity. 52

Table no. Title Page no.

xv

LIST OF GRAPHS



designs using explorer technique. 45


designs using elastomeric disclosing media. 46


designs using stereomicroscope. 47

4. Comparison of mean marginal openings of three designs in

Stereomicroscope by Kruskal Wallis Anova test. 48

5. Percentage of fit and misfit sites in explorer technique. 50

6. Percentage of fit and misfit sites in elastomeric disclosing media 50

7. Percentage of fit and misfit sites in stereomicroscope. 50

xvi

LIST OF PHOTOGRAPHS


1. Materials and armamentarium used 30

2. Armamentarium used 30

3. Stereomicroscope 31

4. Design A 32

5. Design B 32

6. Design C 32

7. Custom tray 33

8. Custom tray with wax spacer 33

9. Impression making 33

10. Final impression 33

11. Pouring of impression using vibrator 34

12. Group of Dies for design A, design B, design C 34

13. Wax coping made using dip wax technique 35

14. Carving Wax pattern 35

15. Wax pattern with margins sealed under 1.5X magnification 35

16. Fit check using explorer 36

17. Fit check using elastomeric disclosing media 36

18. Specimen under stereomicroscope 37

19. Marginal opening as seen under stereomicroscope 38

20. Marginal gap of 30µm, 60 µm, 90 µm as seen under

stereomicroscope 38

1

INTRODUCTION The adaptation of cast restoration to the prepared tooth has been capriciously

defined as “the fit” of the restoration, although precise definition is lacking.

Investigators have described casting fit by mean marginal openings between the

prepared tooth and casting margins,1 by adaptation of multiple points inside the

castings,2 by vertical seating of the casting on prepared tooth or die, or by the distance

from the cavosuface angle of the preparation to the margin of the casting. If a

marginal misfit is viewed as a combination of gap error and extension error, a finite

number of possible types of misfit exist.

Ideally there are no marginal discrepancies between the tooth and restoration and

the emergence profile of the restoration is coincident with sub marginal surfaces of

the prepared tooth. Because of deficiencies inherent in the dental casting technique, a

gap of varying width is likely to occur between a casting and a tooth, both on the

internal surface and at the margins. A luting agent is used to fill this space and

provides both a marginal seal and friction retention for the casting. Cement

dissolution can occur along the casting tooth interface with concomitant risk of caries.

Open marginal configurations encourage micro leakage of bacteria and their by-

products during dissolution of the luting agents. This can cause severe effects on the

health of pulpal tissues.3

There is a continuing quest to determine the best way to minimize the width of

the cement line within accepted technique constraints. Different finish-line designs

have been advocated for several reasons. Preston4 and Shillingburg recommended the

shoulder-bevel as the best type of finish line for the cast restoration. Rosner5 reasoned

2

that a beveled finish line would fit better than a shoulder and trigonometric analysis to

support his assertion. He recommended beveled margin parallel to the axial wall for

smallest possible cement line. Pascoe6 concluded that, with an oversized casting, a

shoulder finish line minimizes marginal opening whereas a beveled shoulder does not.

Others advocated use of shoulder finish lines in metal ceramic technique for

periodontal and esthetic reasons. In view of the limited and contradictory theoretical,

laboratory, and clinical evidence available, it is not clear which finish line design, if

any, may offer the greatest advantage.7

Clinical acceptability and longevity of cast restoration is related to marginal fit.

The result of dental lost wax casting techniques are greatly influenced by the

expansion and contraction of all of the materials used, including impression materials,

waxes, gypsum products, plastics, and metals. In practice, many cast crowns do not

precisely fit on the dies on which they are made. Distortions in the casting results in

non-uniform cementation space and surfaces of actual binding between tooth and

metal. Much of distortion occurs during casting process. Approaches toward

correcting casting-induced errors have involved additive and subtractive techniques.

Additive methods include the use of die spacers,8, 9 a technique that currently enjoys

wide acceptance. Subtractive methods include the bulk etching of internal surfaces by

chemical15 and electrochemical processes. Disclosing materials such as chloroform

with rouge or soft waxes have been advocated for more selective removal of metal,

often at the time of delivery. Elastomeric materials have been recently advocated for

use as a guide during selective internal finishing and visualization of the

precementation space.10, 11

3

Controlled production of a uniform and properly sized precementation space

would seem to be important for (1) initial seating of casting on its dies, (2) appropriate

fluid flow during cementation, and (3) optimized post cementation marginal seal and

occlusal fit of restoration.12

The production of cast restorations with perfect margins is not yet possible.

McLean and Von Fraunhofer found that in vivo marginal discrepancies ranged from

10 to 160 µm. There are several commonly used techniques to evaluate the marginal

accuracy of cast restorations prior to clinical acceptance. These include use of dental

explorer, and elastomeric materials.11, 12, 13

McLean and Von Fraunhofer suggested that a dental explorer could not detect

marginal gaps less than 80 µm. Others have found even greater discrepancies.14 Many

disclosing agents, including chloroform and rouge, disclosing waxes, wax aerosols,

and zinc oxide-eugenol have been used as aids in fitting crowns.15 McLean and Von

Fraunhofer used polyether elastomeric impression material to evaluate the potential

cement film thickness beneath clinical restorations they suggested a further

application of this technique for the placement of cast restorations. This technique

was further described by several authors using a light bodied- condensation reaction

silicone impression material.10, 11, 12

Several studies have reported 30µm to be clinically acceptable gap discrepancy.8

However, there is limited information on sensitivity and specificity of commonly

practiced clinical evaluations (i.e. explorer and elastomeric disclosing material) in

detecting a marginal discrepancy of this magnitude. Sensitivity of a technique is the

probability that there will be a positive result i.e. marginal gap is present between the

casting and prepared tooth. Higher the values of sensitivity lower will be the false

4

negative rate i.e. the tendency of the technique to locate the closely adapted margins

even when marginal gaps are present will be less. The specificity of the technique is

the probability that there will be a negative result i.e. the casting margins are closely

adapted to the prepared tooth. Higher the values of specificity, lower will be the false

positive rate i.e. the tendency of the technique to locate the marginal gap even when

the margins are closely adapted to the prepared tooth will be less.

The indications for the use of die spacers in fabrication of cast restorations are

well documented in the literature.7, 16, 17 In this in vitro study, die spacer was

intentionally not used to create variations in casting fit for the purpose of the study.

The aim of this study was to assess the effect of preparation design on marginal

adaptation, as well as to assess sensitivity and specificity of clinical evaluation of cast

restoration marginal accuracy when compared to stereomicroscopy.

5

OBJECTIVE OF THE STUDY

The aim of this study was to assess the effect of preparation design on marginal

adaptation, as well as to assess sensitivity and specificity of clinical evaluation of cast

restoration marginal accuracy when compared to stereomicroscopy.

6

REVIEW OF LITERATURE

A study investigated four representative casting techniques to determine if a number

of castings made by these techniques would be dimensionally same. The conclusions

derived from this study were:

• The variations in the size between a number of castings made by a present day

dental casting techniques may be of order of 1.0 per cent.

• The inherent surface roughness or texture of the casting will appreciably affect

the subsequent fit.

• A problem of obtaining uniform expansion exists when making full crowns

and probably mesioocclusal distal inlays by hygroscopic compensating

techniques.18

An article described a clinical procedure for making precision casting restorations.

The procedure follows the conditions specified in previous experimental research.

Consistent success has been obtained by this technique, with minimal amount of time,

labour, and materials.19

An article discussed the function, placement, and reproduction of bevels for gold

castings. Castings have inherent errors of a significant character. The preparation of

teeth should be modified to cancel errors as much as possible, and to make use of

certain specific properties of gold castings.5

7

A study investigated the factors governing the resistance of the cementing medium in

the placement of full crowns by measurement of the thickness of the cement on

cervical shoulders of the preparations of various types. Techniques to relieve the

resistance of the cement within the crowns were developed. Conclusions derived from

this study were:

• The Excessive amount of pressure during cementation produced no

significant difference in the thickness of the cement on the shoulders of

the preparations.

• An increase in taper of the walls of the preparation resulted in marked

decrease in the thickness of the cement on the shoulders.

• A decrease in the height of the preparation slightly decreased the

thickness of cement on the shoulders.

• Relief spaces made on the inside surfaces of the crowns to reduce the

resistance of cement markedly reduced the cement thickness on the

shoulders.

• No significant difference was found between two types of application

of a relief material in the seating of crowns. However, the buccolingual

application of tinfoil was the most simple to use clinically.

• Cement exposure was greatest on the shoulder type of preparations,

much less on the chamfered type, and very little on the shoulder less

type. 20

A study was done to evaluate microscopically the marginal opening, termed clinically

acceptable by ten experienced dentist, who also evaluated the marginal adaptation of

visually accessible and inaccessible gold inlay margins by explorer. The study also

8

determined if gold inlay margins may be closed past the film thickness of zinc

phosphate cement by proper finishing and polishing. The conclusions of the study

were:

• The least acceptable, visually accessible margin was computed from a linear

regression prediction formula to be open 39µm. The range of opening of 40

barely clinically acceptable margins was from 2 to 51 µm.

• There is direct relationship between the microscopic opening of visually

accessible occlusal and proximal gold inlay margins and the experienced

restorative dentists ability to evaluate this opening clinically by sight and

explorer.

• The dentists were not able to evaluate consistently the marginal opening of

gingival areas by explorer or roentgenogram.

• Margins closed past the reported film thickness of zinc phosphate cements if

proper finishing techniques are used.

• Explorer examination of visually accessible gold inlay margins is superior to

and more reliable than, explorer or roentgenographic examination of visually

inaccessible margins.14

A study compared the fit of certain casting alloys, investments and techniques.

Alloys and combinations used were- (1) Micro-bond Platinum series alloy and

investment, (2) Ney G 3 Gold and Cristoballite investment, (3) Ney G 3 Gold and

Whip-mix Hydrotrol investment, (4) Ceramo no.1 alloy and whip-mix cermigold

investment, (5) Ceramo no.1 alloy And ransom-Randolph H.F.G investment.

Conclusions drawn from this study were:

• All castings evaluated in this study failed to seat precisely.

9

• The most superior castings from the standpoint of overall adaptation to the

dies were those made with Ceramco No.1alloy and Whip-Mix Ceramigold

investment.

• Results achieved with the cristobalite and H.F.G. investment alloy were

comparable.

• The results produced by the Micro-bond investment-alloy combinations were

felt to unsuitable for general use.

• The Hydrotrol investment-alloy combination produced the worst results in this

study. The use of this investment without water bath provided insufficient

expansion.

• Binding occurred towards the occlusal end of nearly all castings.

• The MOD castings showed a definite pattern of distortion.

• Phosphate and ethyl silicate bonded investments produced 1.0 % more

expansion than gypsum bonded.

• Proximal lengths of the MOD castings were all shorter than corresponding

length of dies.

• The definition of casting accuracy should take into consideration a degree of

fit rather than absolute adaptation.21

An article described methods for achieving a better fitting restoration with more

closely adapted margins. They were:

• Silver-plated dies are used for better marginal detail.

• Water swaged patterns are used for closer adaptation; then the margins are

overwaxed.

10

• The internal surface of the casting is relieved, except for the margins. This will

allow cement to flow more easily for better seating.

• Vise-seat the inlay on the silver-plated die, trim the margins, burnish-fit the

margins, then polish the casting on the silver die.

• Use an exacting cementation procedure.22

A study was done to determine relationship between preparation finish line

configurations and marginal stability of porcelain-fused-to-metal restorations during

firing cycle. The study concluded that shoulder finish lines, with or without bevel,

were found to produce significantly less distortion in labial margins of porcelain-

fused to-metal restorations than do chamfer finish lines with and without a bevel. 23

A study determined the influence of crown-margin location on the gingival tissue for

cast complete crowns. A comparison of the two margin locations using four different

methods of evaluation revealed no difference (1) in health of the gingival tissues, (2)

in change in sulcus depth, (3) in gingival contour, and (4) in plaque accumulation.

This study suggested that the fit and finish of full crown restorations may be more

significant to gingival health than location of the finish line. 24

An article discussed the factors that determine an adequate preparation for

ceramometal restorations. The factors include margin design, margin placement and

technique and instrumentation during tooth preparation. When all physical and

biologic requirements of tooth preparations are considered, and the preparation is

approached as a concept rather than simply a technique, it is possible to provide

11

foundation for desirable esthetic form, to develop strength compatible with function,

and to preserve the attachment apparatus of the supporting tooth.4

A study analyzed the geometry of finish lines for full crown restorations. And

concluded that the geometry exhibiting least marginal discrepancy was shoulder of

slightly oversized casting. This was significantly better than oversize bevel, the control

shoulder, or the control bevel.6

A study describes methods for eliminating the effect of internal discrepancies which

cause a rebound effect, requiring occlusal reduction and adjustments of faulty margins.

And concluded that a die relief method was found to be most suitable of the three

casting compensation techniques.8

A study examined the influence of the marginal design on occlusal seat and marginal

seal of a cemented full crown restoration. Featheredge and parallel bevel preparations

demonstrated the best marginal seal, followed in order by the full shoulder, 45-degree

shoulder, and finally the 90-degree shoulders with 30-degree and 45-degree bevels.

With regard to seating of the restoration, the 90-degree full shoulder demonstrated the

best seat, followed in order by 45-degree shoulder, 90-degree shoulder with 45-degree

bevel featheredge, 90-degree shoulder with 30-degree bevel, chamfer with parallel

bevel, and finally 90-degree shoulder with parallel bevel.25

An investigation was done to determine which metal and coping design combination

consistently provided optimum marginal accuracy and esthetics. The study concluded

that:

12

• Hollow grinding provides an adequate preparation for anterior ceramometal

restorations.

• Nonprecious (ni-cr) alloys can cast accurate as semiprecious or precious

ceramoalloys.

• Metal distortion is not significant in a collarless or a collar coping design, if

0.4 mm metal thickness is used.

• Collarless, facially butted porcelain ceramometal crowns are clinically

unacceptable.

• A hairline metal-collar coping design is recommended for hollow-ground

preparations where a nonprecious alloy is used.26

An article described a technique for mounting and refining multiple restorations

(castings) to a high degree of accuracy. The remounting procedure is used to correct

dimensional changes of the impression material, die stone, wax, investment, and alloy

shrinkage that occur in making the castings. The technique offers a solution to many

problems encountered when making final adjustments in the mouth.15

A study evaluated the phosphate-bonded investment and a calcium-bonded investment

for surface smoothness and marginal fit they impart to type III gold castings. The

conclusions of the study were:

• The marginal fit with the phosphate-bonded investment method was superior

to that obtained with the calcium sulphate-bonded investment.

• Surface roughness was greater for the castings with the phosphate-bonded

investment when measured with SEM photographs and visual observation.

13

• The phosphate-bonded investment increased the incidence of nodules on the

surface of the castings.

• No correlation was demonstrated between marginal fit and surface roughness

or the incidence of nodules on the castings.27

A study was done to evaluate the agreement within and between experienced dentists

when using an explorer to identify the maximum size of acceptable openings of

nonvisible margins. The study concluded that there was significant inconsistency

within and among members of the faculty as to the maximum opening acceptable and

more reliable methods are needed for evaluating nonvisible margins of castings before

cementation.1

An article describes the use of an elastic material of room-temperature vulcanizing

(RTV) silicone type as a displaying medium, an aid in fitting the castings. The

primary advantage of this technique is that it enables the practitioner to accurately

visualize the final cement displacement and thereby improve the physical fit of the

restoration. Margins are rarely altered, but inferior modifications are a beneficial

adjunct to complete seating and marginal integrity.10

An article described that a full veneer preparation with a beveled gingival margins

combined with a differentially oversized casting has shown to offer theoretic potential

for:

• Minimizing marginal discrepancies

• Decreasing the incidence of overhangs

• Minimizing the effects of variations in casting size.28

14

An article describes a clinical method for efficient and accurate assessment of the

marginal integrity of cast restorations using light-bodied elastomeric material. An

acceptable cast restoration fabricated with die relief should express all elastomeric

material along the bevel. This is evident with this technique.11

A study compared the adaptation of the margins of gold crowns produced from three

impression-die combinations. The study concluded that crowns produced on silver

dies from polysulfide impressions had a smaller marginal opening than the crowns

made on dies of improved stone.2

A study was done to determine the influence of the die relief agent on the retention of

cast restorations using three cementing mediums. The study concluded that die relief

agents resulted in a 32% reduction in the forces required to dislodge castings

cemented with zinc phosphate. Other cements did not differ statistically.9

A study examined the comparative fit in vivo of three types of PFM crown margins.

Marginal openings were measured with SEM on replicas derived from elastomeric

impressions. And concluded that there was no significant difference among beveled

metal margins, metal butt margins, or porcelain butt margins either before or after

cementation at 95% confidence level. It is possible under clinical conditions to

consistently produce porcelain butt margins with less than 50µm marginal opening in

PFM restoration.16

15

A study was done to correlate the marginal fit of full cast crowns made by

commercial dental laboratories with the design of the margin. The conclusions of the

study were:

• Margins prepared with unbeveled heavy chamfers and shoulders were most

likely to have openings that exceeded 39µm on the dies. They were also most

likely to have metal flash left on the margins.

• Knife edged and beveled margins were least likely to have metal flash or

openings that exceeded 39µm on the dies.29

A study determined whether internal relief compensated for the restrictive effects of

grooves on seating of complete cast crowns. The study concluded that:

• Die relief significantly improved the seating of complete cast-gold crowns

with or without grooves.

• Omitting die spacer from grooves did not reduce the benefits of

relieving the remainder of the die.

• The grooves did not disrupt seating when die spacer application was

complete or specifically omitted from the grooves alone.17

A study on method to improve the fit of castings by use of elastomeric impression

materials was done, and it was found that condensation polysilicone impression

material is well suited to meet the requirements of an ideal disclosing material. A two

fold improvement in marginal seal and occlusal seat was achieved in the experimental

castings compared with the control castings.12

16

A study was done to determine whether the use of a silicone fit-indicator leaves a

residual film in a metal casting and to measure the potential effect of this residual film

on the retention of a cemented core. The study concluded that these indicators seem to

leave a residual film that significantly reduces crown retention. Gross mechanical

removal and use of an organic cleaning solution proved ineffective in removing the

residual silicone.30

A study examined relationship between marginal adaptation of dental casting and

periodontal tissue health. And concluded that an increase in marginal discrepancy

between dental casting and prepared tooth resulted in an increase of gingival

inflammation measured by a gingival index and crevicular fluid volume.3

A study measured and compared the marginal accuracy of complete crowns made

from low-gold and base metal alloy systems with that of cowns from traditional type

III high gold alloy. The findings of the study indicated that Ag-Pd alloy crowns

exhibited the best marginal accuracy among the alternative alloys tested. However,

their marginal discrepancy value was still slightly higher than that of the crowns made

of type III high-gold-alloy. Conversely, Ni-Cr-Mo alloy crowns exhibited the poorest

marginal accuracy.31

A study was conducted to determine the effectiveness of a silicone disclosing

medium, G-C fit-checker, as an aid in improvement of marginal integrity. The

preadjustment mean marginal opening was 92 microns and the post adjustment

measurement 55 microns, yielding a mean reduction of 37 microns (SEM 3 microns)

or 39%. 13

17

A study evaluated axial and marginal fit of crowns made for three tooth preparations

that had different labial finish lines configuration: shoulder, shoulder-bevel, and

chamfer. There were no significant differences (p< or =.05) among groups for

marginal and axial gaps. The study concluded that crown fit was not influenced by

any of the three finish lines tested, and castings with well fitted margins exhibited

measurable axial wall space.7

A study was done to determine the effect of two impression materials used in three

different techniques for the accuracy of the marginal fit of metal castings. The

following method was used(1) putty in a metal stock tray with simultaneous

elastomeric impression wash, (2) copper band relined with Autopolymerizing acrylic

resin and subsequent light-body elastomeric impression material, and(3) copper bands

with modeling compound. There were no statistically significant differences between

various impression materials, techniques, and facial and lingual surfaces.32

A study was done to evaluate the marginal discrepancy and surface roughness of

complete crowns made with an accelerated casting technique, that uses four phosphate

–bonded investments and a high noble metal ceramic alloy. Comparisons between the

conventional and accelerated casting techniques were made for each investment and

among investment. The following conclusions were drawn:

• There was no statistical difference in the marginal discrepancy of cast crowns

made by using accelerated technique as compared with conventionally made

crowns.

• Differences in the average surface roughness of cast crowns were not detected

between the accelerated and the conventional techniques

18

• Clinically acceptable complete castings can be obtained with the accelerated

technique if optimum heating conditions are selected for each investment.33

A study done to measure the marginal gaps and to determine clinical acceptability of

single-unit castings invested in a phosphate bonded investment by using conventional

and accelerated methods.

• Marginal gaps for castings made with an accelerated technique showed no

statistical difference when compared with a conventional casting group.

• The accelerated casting technique offers a cost-effective and time-saving

method by which single-unit castings for metal/ceramic crowns can be

fabricated.

• The methods used for accelerating the casting process are technique sensitive.

Minor variations in the procedures can cause casting defects such as nodules,

fins, and porosity.34

A study compared, in vitro, the marginal fit of 4 types of complete crowns on human

premolar teeth with the use of nondestructive profilometry. This method determined

whether fit was influenced by type of crown or surface morphology of the tooth,

namely, grooved or ungrooved surfaces. The study concluded that:

• For each specimen, there was considerable variation from profile to profile in

marginal fit of crown-to-tooth preparation, with rapid changes between

underextension and overextension.

• Very few crown profiles achieved a perfect vertical or horizontal overlap.

• Effect of surface type, grooved or ungrooved, was not significant.35

19

A study investigated the compositional stability of a commercial type III gold alloy

with different casting protocols and to examine the influence of casting protocol on

the marginal accuracy of complete cast crowns. The study concluded that recasting

type III gold alloy may adversely affect the marginal accuracy of complete cast

crowns. However, in this study, such effects were not clinically significant.36

A study was done to verify the influence of casting techniques on the internal and

cervical fitting of the complete cast crowns, applying die-spacer material to the die

prior to the fabrication of the wax pattern, or removing metal from the interior of the

casting before cementation by abrading with aluminium oxide particles or chemical

etching with nitric acid. The study concluded that the best marginal and inner fits

were obtained with gas-oxygen torch source. The 45-degree chamfered shoulder

showed the best marginal and inner fit, and better internal relief was obtained in the

crowns abraded with 50µm Al2O3 particles.37

An in vitro study evaluated the marginal adaptation and fracture strength of ceramic

optimized polymer (ceromer)/ fiber reinforced composite ( FRC) crowns with respect

to the various types of finish lines. The study concluded that marginal gaps were

greater for the chamfer finish line specimens than in the shoulder finish line

specimens. However, the fracture strength of the chamfer finish line specimens was

greater than that of the shoulder finish line specimens.38

A study compared the marginal accuracy of posterior metal ceramic(MC), all-ceramic

IPS Empress2, and experimental pressed ceramic(EPC-VP 1989/4)three unit fixed

partial dentures(FPD), before and after luting and after thermo-mechanical fatigue in a

20

dual-axis chewing simulator. The study concluded that marginal gap values of these

all-ceramic materials and conventional MC techniques are on a similar level. In

particular, almost all marginal gap values observed in this study were within the limits

of clinical acceptance.39

A study was done to analyze the influence of marginal design on maginal accuracy of

a casting in a clinical set up of patients. Three different types of finish lines-chamfer,

135 º shoulders, and 90º shoulder were employed. The difference between the three

different preparation types was significant. The lowest median values were obtained

for the chamfer preparations, while the 90º shoulders always produced the highest

median values. The study concluded that marginal designs had much less influence on

the marginal fit of high non precious alloy castings than expected. There is

considerable reason to assume that technical but clinical parameters influence the

quality of fixed prosthodontics much more than has been believed in the past.40

A study assessed the effect of preparation design on marginal adaptation. In addition,

sensivity and specificity of clinical evaluations of marginal adaptations of cast

restorations were assessed and compared to stereomicroscopy. The study concluded

that the preparation design does not significantly affect the marginal adaptation.

Clinical detection, with similar sensivity and specificity as the stereomicroscope,

occurred at marginal openings greater than or equal to 124 µm. Therefore, commonly

used clinical evaluation techniques using an explorer and disclosing media may be

inadequate for assessments of marginal accuracy.41

21

A study was done to evaluate the influence of investment type and number of sprues

on accuracy of crown castings made with commercially pure titanium. The study

concluded that:

• The magnesium oxide-bonded investment (Rematitan Ultra) provided

significantly better casting accuracy for CP titanium crowns compared to the

monoammonium dihydrogenphosphate-bonded investment (Rematitan plus).

• The marginal accuracy of crowns cast with CP titanium was significantly

better when 2 sprues were used rather than one.

• The monoammonium dihydrogenphosphate-bonded investment (Rematitan

plus) provided casting accuracy similar to that obtained with the magnesium

oxide-bonded investment (Rematitan Ultra) when 2 sprues were used in

casting CP titanium crowns.42

22

MATERIALS AND METHOD

This invitro study was carried out in Department of Prosthodontics, P.M.N.M. Dental

College and hospital, Bagalkot.

MATERIALS USED:

Following materials were used:

MATERIALS MANUFACTURER BATCH

NO.

Ivorine molar teeth Columbia Dentoform corp.

Autopolymerizing acrylic resin DPI-RR cold cure-acrylic repair

material.

1274

Modelling wax Maarc, India 0035

Tray adhesive Dentsply International, U.S.A 050418

Medium body Addition silicone

impression material

Aquasil, Dentsply International,

U.S.A

070612

Type IV Gypsum product Pearl stone, Asian chemicals,

Gujarat, India

50589

Type II Blue Inlay waxes MDM. Corp. 0010968

Investment material Moldavest exact; Heraeus

kluzer,Germany

2653230

Non precious gold alloy FGC Copper Alloy,

AalbaDent , Brazi l .

2000509

Elastomeric Disclosing media fit checker II; GC Tokyo, Japan 0707042

http://www.aalbadent.com.br/

23

ARMAMENTARIUM USED:

1. Air rotor hand piece (NSK, Japan)

2. Diamond burs (shofu crown and bridge preparation kit)

3. Rubber bowls, plaster spatula, lacrons carver, BP blade and scalpel

4. Vaccum mixer (V-Mix, yoshida)

5. Vibrator (J- Morita corp.)

6. Waxing heater (SW-50 SPM)

7. Electric waxing up instruments (Renfert, Germany)

8. Casting machine (Ducatron serie 3)

9. Burnout Oven (VULCAN 3-550 Ney)

10. Explorer (Explorer AMP No. 5 Dentsply)

11. Glass slab and metal spatula

12. Stereomicroscope (Lawerence & Mayo, India)

METHOD FOLLOWED:

The method involved the evaluation of the marginal fit of cast restorations. Eight

specimens of three different preparation designs were made, and castings were

examined using an explorer, disclosing media, and a stereomicroscope for marginal

adaptation.

1) PREPARATION OF TEETH

Three Ivorine maxillary first molar teeth were selected for study and were mounted

by securing roots with wax. The roots were then invested in dental stone (Kalstone,

Kalabhai India). A flat base was made in dental stone, 15 mm below the cervical

portion of the invested ivorine tooth which acts as stopper during the placement of

24

impression tray. These three ivorine teeth were then prepared with three different

designs:

Design A- A complete crown preparation with a buccal shoulder (1mm wide)


Design B - A complete crown preparation with a chamfer finish line.

Design C- A three-quarter crown preparation with proximal boxes and beveled

finish line.

Standardized tooth preparations were performed using a air turbine dental hand

piece using diamond points with the aid of paralleling device. A cone angle of 6

degrees and a preparation height of 4mm, (measured at the midfacial surface of the

tooth), were used. Tooth preparations were done by one operator to eliminate

operating variables in multiple tooth preparations.

2) FABRICATION OF CUSTOM TRAY

To fabricate a custom tray, initially two layers of modeling wax (Maarc, India) was

adapted over the prepared ivorine teeth for each design as a spacer. The custom tray

was made with autopolymerizing acrylic resin (DPI-RR cold cure-acrylic repair

material). The custom tray was bench cured for 24 hours. Eight custom trays were

made for each preparation design, thus total of 24 custom trays were fabricated. All

custom trays were finished and kept ready for making impressions.

3) IMPRESSIONS OF TEETH

The ivorine teeth were thoroughly cleaned using damp cotton cloth before making

impressions. The custom trays were then coated with tray adhesive (Dentsply

International, U.S.A) after removal of wax spacer. Medium body addition silicone

25

impression material (Aquasil, Dentsply International, U.S.A) was mixed according to

manufacturers instructions. The custom tray was filled with impression material and

was seated on the prepared ivorine teeth with adequate finger pressure till the

resistance of the stopper is felt and the tray surface comes in even contact with dental

stone block. The custom tray was held in position until the impression material sets.

After setting impression was removed and inspected for any defects under 1.5X

magnification. Thus total of 24 impressions were made with 8 in each of preparation

design.

4) DIE PREPARATION

The type IV die stone (Pearl stone, Asian chemicals, Gujarat, India), with a water-

powder ratio of 25cc/100 gms was mechanically mixed using vaccum mixer, and

poured into the impression using vibrator. After final set, dies were recovered. The

dies were inspected for any discrepancies under 1.5X magnification. They dies were

numbered and three groups were formed according to preparation designs, with eight

dies in each group. Thus a total of 24 dies were prepared.

5) FABRICATION OF WAX PATTERN AND INVESTMENT

An even application of die lubricant (Die Lube Wax Sep. Dentecon, U.S.A) was

done on each die. Wax patterns were fabricated on the dies using type II blue inlay

wax (MDM. Corp.). Dip wax technique was used to form wax copings. The copings

were continued to be dipped until there was sufficient bulk from which final pattern

was carved. The patterns were contoured parallel to the emergence profile and

margins were manually sealed under 1.5X magnification as accurate wax pattern

26

which showed no marginal discrepancy was mandatory. Wax patterns were carefully

removed from the dies so as to minimize distortion of patterns.

Sprue wax of diameter 2.5 mm was attached to the occlusal surface of each pattern

on the non functional cusps and was angled so that it was obtuse to the adjacent axial

walls and occlusal surface. Each Wax pattern was invested immediately in phosphate-

bonded investment with the powder liquid ratio was 60g of powder to 12 ml of liquid,

after cleaning it using wax pattern cleaner (Jelenko), this reduces the surface tension

of wax and permits better wetting. The investment material was mechanically

spatulated under vaccum spatulation time for 90 seconds. The wax patterns were

carefully painted with the investment mixture by means of fine sable hair brush. The

casting ring lined with cellulose acetate ring liner was then filled with the investment

material under mechanical vibration and allowed to set on the bench for 1 hour. All

procedures were carried out by one operator.

6) FABRICATION OF CASTINGS

The rings were then, placed in an oven (VULCAN 3-550 Ney). A standardized

burn out and preheat procedure of 30 minutes at 23º-270º C, 30 minutes at 270º-580º C,

and 30 minutes at 580º-950ºC, was followed. Casting was accomplished in an

induction centrifugal casting machine (Ducatron serie 3) using non precious gold

alloy with a composition of 80.07% copper, 7.80% Al, 3% Fe, 2.70% Zn, 1.70%Mn,

4.30% Ni. Castings were devested, cleaned, and air abraded with 50 microns

aluminium oxide at 0.6 Mpa, (fine grit, jelenko quartz abrasive; Armonk, NY). Sprues

were removed using silicon carbide disks, and the castings were finished externally

using blue, green, and brown rubber wheels. Internal positive defects were removed

using a ½ round bur under 1.5X magnification.

27

Castings were ultrasonically cleaned in distilled water and stored until further

evaluation

7) MEASUREMENT OF MARGINAL FIT

Each casting underwent examination with an explorer, elastomeric disclosing

media (fitcheckerII), and a stereomicroscope.

One examiner performed the clinical evaluations with an explorer and disclosing

media. The examiner made a list of 20 sites without prior observation or examination

of specimens to select 20 random sites for initial examination. These sites were then

used to determine intraoperator reliability, which is established to be 95%. The

reliability of stereomicroscope approximated 100%.

Twelve circumferential recordings were made of each casting, three on each

buccal, lingual, mesial and distal surface, marked with a groove on original ivorine

teeth and highlighted using a fine indelible marker, for a total of 288 examination

sites.

Evaluation of marginal adaptation using Explorer

Margins were evaluated by examiner relying on his tactile sense with great

concentration. Examiner evaluated the margins by feeling it with explorer. Same

explorer was used to evaluate all castings for the purpose of standardization. Explorer

misfit was defined as any of the following: clinically unacceptable vertical marginal

discrepancy, horizontal marginal discrepancy, under extended margins, and seating

discrepancy examined at original magnification ×1.5.

28

Evaluation of marginal adaptation using Elastomeric Disclosing Media

Material (fit checker II; GC Tokyo, Japan) was manipulated according to

manufacturer’s instructions. Each experimental casting was filled with disclosing

material then seated on the respective ivorine teeth with finger pressure appropriate to

seat the casting on prepared tooth. An area was interpreted as “fit” if the seal of the

casting is observed to be apparent by clearly identifiable thin translucent film. Areas

where the film is very thin or thick indicate “misfit”.

Evaluation of marginal adaptation using Stereomicroscope A stereomicroscope (Lawerence & Mayo, India) was used to examine these twelve

circumferential sites at 30X magnification. The recordings were made and interpreted

using software (ImageJ 1.40g U.S.A). Stereomicroscopy at a value less than or equal

to 30 microns measurements was used as a gold standard to evaluate the significance

of different designs on marginal adaptation. Three sites for each buccal, lingual,

mesial, and distal surface were given an overall evaluation of acceptable or

unacceptable. Since in a clinical situation adequacy of marginal accuracy at each

point is desired, these values were not averaged; instead a surface was ranked as fit

where all 3 measurements were less than or equal to 30 microns using

stereomicroscopy. If any of the 3 measurement points had a value of greater than 30

microns that surface was ranked as misfit.

Chi-square tests of independence and kruskal-Wallis were performed at a priority

level of significance of =0.05 to determine the significance of each surface (buccal,

lingual, mesial, and distal) and overall design with respect to marginal adaptation.

Further Chi-square tests of independence were used to compare agreement between

29

stereomicroscope, explorer, and disclosing media detection of marginal gaps less than

or equal to 30 microns.

Sensitivity and specificity for explorer and disclosing media as compared to

stereomicroscope was calculated using statistical formula given by Park.43

39

RESULTS

Table1, 2, 3 shows the readings of all three preparation designs using Explorer,

elastomeric disclosing media and stereomicroscope respectively.

Table 4 shows the distribution of overall marginal adaptation of crowns by three

designs using explorer technique.

For Design A 12.50% were misfit and 87.50% fit.

For Design B 25.00% were misfit and 75% fit.

For Design C 37.50% were misfit and 62.50% fit.

On comparison using chi-square test of independence, the three designs showed no

significant difference on marginal adaptation using explorer technique with p-value

0.5134. The results were shown in the graph 1.


designs using elastomeric disclosing media

For Design A 0% was misfit and 100% fit.

For Design B 0% was misfit and 100% fit.

For Design C 0% was misfit and 100% fit.


significant difference on marginal adaptation using elastomeric disclosing media with

p-value 1.0000. The results were shown in the graph 2.


designs using stereomicroscope

40

For Design A 100% were misfit and 0% fit.

For Design B 87.5% were misfit and 12.5% fit.

For Design C 100% were misfit and 0% fit.


significant difference on marginal adaptation using stereomicroscope with p-value

0.352. The results were shown in the graph 3.

In table 7 the mean marginal openings of three designs in Stereomicroscope is

compared for statistical analysis using kruskal wallis Anova test. The three designs

showed no significant difference in the mean marginal opening with p-value 0.1197.

The results were shown in the graph 4.

Thus the preparation design did not significantly affect overall marginal adaptation.

Table 8 shows the marginal accuracy findings on buccal, lingual, mesial, distal

surfaces of three preparation designs. Analysis of different surfaces revealed no

significant difference in marginal adaptation for the three designs examined.

Table 9 shows the percentage of 288 sites with inadequate marginal fit as detected by

explorer, elastomeric disclosing media, and stereomicroscope.

Explorer detected 33.33% of misfit sites.

Elastomeric disclosing media detected 10.06% of misfit sites.

Stereomicroscope detected 79.16% of misfit sites.

Graph 5, 6, 7 shows the percentage of fit and misfit sites for each of the three

techniques.

41

Table10 shows the overall agreement between the stereomicroscope and explorer was

50.69%, with a 19.09% correct acceptance rate (19.09% of the time the explorer

ranked “fit” and the stereomicroscope showed a gap size of less than or equal to

30µm) and 31.59% correct rejection rate (31.59% of the time the explorer ranked

“misfit” and the stereomicroscope showed a gap size of greater than 30µm).

Table11 shows the overall agreement between the stereomicroscope and elastomeric

disclosing media was 29.16%, with a 19.09% correct acceptance rate (19.09% of the

time the elastomeric disclosing media ranked “fit” and the stereomicroscope showed a

gap size of less than or equal to 30µm) and 10.06 % correct rejection rate (10.06 of

the time the elastomeric disclosing media ranked “misfit” and the stereomicroscope

showed a gap size of greater than 30µm).

Illustrations 1 & 2 shows that the explorer at 30µm had 39% sensitivity and 91%

specificity and elastomeric disclosing media had 10% sensitivity and 82% specificity

respectively.

42

Table 1: Readings of all three preparation designs using Explorer




Design C- A three-quarter crown preparation with proximal boxes and beveled finish

line.

SPECIMEN NO.

DESIGN

SURFACE

SITES 1 2 3 4 5 6 7 8

1 F F F F MF MF MF MF 2 F F F F MF MF MF MF BUCCAL

3 F MF F F MF F MF MF 1 F MF MF F F F F F 2 F MF MF F F F F F LINGUAL

3 F MF MF F F F MF F 1 F F MF MF F F MF MF 2 F F F F F F MF F MESIAL

3 F MF F F MF F F F 1 F F F MF F F F F 2 F F MF F F F F F

Design A

DISTAL

3 F F MF F MF MF F F 1 MF F F MF F F F F 2 MF MF F F F F F F BUCCAL

3 MF F F F F F F F 1 MF MF F MF F MF F MF 2 MF F F MF F F F MF LINGUAL

3 MF F F MF F F F MF 1 MF F F F F MF F F 2 MF MF F F F MF F F MESIAL

3 MF F F F F MF F MF 1 F F F F F F F MF 2 F F F F F F F MF

Design B

DISTAL

3 F F F F F F F MF 1 F F F F F F MF F 2 F F F MF MF F F F BUCCAL

3 F F F MF F F F F 1 MF F MF MF MF MF F F 2 MF MF MF MF MF MF F MF LINGUAL

3 MF F F F MF MF MF MF 1 MF MF F MF MF F F MF 2 F F F F MF F F F MESIAL

3 MF F MF F MF F MF MF 1 F F F F F MF MF MF 2 F F F F F F F MF

Design C

DISTAL

3 MF F MF F F F F F

43

Table 2: Readings of all three preparation designs using Elastomeric disclosing media





line.

SPECIMEN NO.

DESIGN

SURFACE

SITES 1 2 3 4 5 6 7 8

1 F F F F MF F MF MF 2 F F F F MF F MF F BUCCAL

3 F F F F MF F F F 1 F F F F F F F F 2 F F F F F F F F LINGUAL

3 F F F F F F F F 1 F F F F F F MF F 2 F F F F F MF F F MESIAL

3 F F F F F F F F 1 F F F MF F F F F 2 F F F F F F F F

Design A

DISTAL

3 F F F F F F F F 1 MF F F F F F F F 2 MF F F F F F F F BUCCAL

3 MF F F F F F F F 1 MF MF F F F F F F 2 F F F F F F F MF LINGUAL

3 F F F F F F F F 1 F F F F F F F F 2 F F F F F F F F MESIAL

3 F F F F F F F MF 1 F F F F F F F MF 2 F F F F F F F MF

Design B

DISTAL

3 F F F F F F F MF 1 F F F F F F F F 2 F F F F F F F F BUCCAL

3 F F F F F F F F 1 F F MF MF F F F F 2 MF F MF MF F MF F F LINGUAL

3 MF F MF F F F F F 1 MF MF F F F F F F 2 F F F F F F F F MESIAL

3 F F F F F F F F 1 F F F F F F F F 2 F F F F F F F F

Design C

DISTAL

3 F F F F F F F F

44

Table 3: Readings of all three preparation designs using Stereomicroscope





line.

SPECIMEN NO.

DESIGN

SURFACE

SITE 1 2 3 4 5 6 7 8

1 60 39 30 63 119 130 130 126 2 32 60 30 60 128 120 128 140 BUCCAL

3 18 125 30 30 120 84 124 128 1 58 128 118 30 68 44 30 60 2 62 115 120 30 63 21 48 30 LINGUAL

3 75 120 128 48 30 51 124 62 1 58 45 120 124 52 48 120 123 2 42 45 12 60 48 112 128 28 MESIAL

3 60 118 30 63 124 58 68 30 1 28 120 15 119 56 73 30 83 2 9 45 120 15 48 92 28 98

Design A

DISTAL

3 15 124 130 66 124 130 30 21 1 153 27 35 45 28 60 33 63 2 123 75 75 30 51 28 38 48 BUCCAL

3 120 26 63 32 42 75 76 75 1 141 123 36 87 12 125 26 125 2 124 54 45 60 12 48 18 122 LINGUAL

3 123 39 30 42 45 30 26 128 1 125 15 42 51 72 128 70 90 2 129 125 36 88 57 131 53 51 MESIAL

3 38 33 36 84 48 124 60 132 1 30 57 81 93 93 27 60 128 2 54 58 60 69 54 35 62 124

Design B

DISTAL

3 30 76 57 90 58 27 60 124 1 60 30 48 39 33 39 125 35 2 72 58 81 126 123 35 72 30 BUCCAL

3 21 24 36 124 27 8 34 22 1 123 72 123 141 125 127 77 88 2 141 128 183 144 129 201 87 120 LINGUAL

3 123 48 102 66 124 124 125 130 1 123 118 45 148 126 77 93 78 2 45 21 31 10 124 74 94 99 MESIAL

3 79 30 128 45 128 54 104 137 1 57 15 63 16 96 128 87 125 2 51 48 36 27 45 30 15 134

Design C

DISTAL

3 123 39 128 63 87 28 30 48

45

Table 4: Distribution of overall marginal adaptation of crowns by three designs using

explorer technique

Designs Misfit % Fit % Total

Design A 1 12.50 7 87.50 8

Design B 2 25.00 6 75.00 8

Design C 3 37.50 5 62.50 8

Total 6 25.00 18 75.00 24

Chi-square= 1.3330 df=2 p=0.5134, NS

1

7

2

6

3

5

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

No

of su

bjec

ts

DESIGN A DESIGN B DESIGN C

Graph1:Distribution of over all marginal adaptation of crowns by three designs using explorer technique

Misfit Fit

46


elastomeric disclosing media


Design A 0.00 0.00 8 100.00 8

Design B 0.00 0.00 8 100.00 8

DesignC 0.00 0.00 8 100.00 8

Total 0.00 0.00 24 100.00 24

Chi-square= 0.0000 df=2 p=1.0000, NS

0

8

0

8

0

8

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

No

of su

bjec

ts


Graph2:Distribution of overall marginal adaptation of crowns by three designs using elastomeric disclosing media

Misfit Fit

47


Stereo Microscope


Design A 8 100 0 0 8

Design B 7 87.5 1 12.5 8

Design C 8 100 0 0 8

Total 23 96 1 4 24

Chi-square= 0.0000 df=2 p=0.352, NS

8

0

7

1

8

00.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

No

of su

bjec

ts


Graph3:Distribution of overall marginal adaptation of crowns by three designs in stereomicroscope

Misfit Fit

48

Table7: Comparison of mean marginal openings of three designs in Stereomicroscope

by Kruskal Wallis Anova test

Designs Means Std.Dev. Sum of Ranks

Kruskal-Wallis

test: H -value p-value

Significance

Design A 63.92 29.60 93.00

Design B 64.45 17.68 75.00

Design C 81.75 14.67 132.00

Total 70.04 22.33

4.2450 0.1197 NS

63.92

29.6

64.45

17.68

81.75

14.67

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

Mea

n va

lue


Graph4:Comparison of mean marginal openings of three designs in Stereomicroscope

Means Std.Dev.

49

Table 8: Marginal accuracy findings on buccal, lingual, mesial, distal surfaces of

three preparation designs.

EXPLORER Buccal Lingual Mesial Distal Design

FIT MISFIT FIT MISFIT FIT MISFIT FIT MISFIT

Design A 5 3 3 5 4 4 7 1 Design B 3 5 5 3 2 6 4 4

Design C 5 3 0 8 1 7 6 2

p=0.511, NS p=0.028, NS p=0.244, NS p=0.244, NS

ELASTOMERIC DISCLOSING MEDIA

Buccal Lingual Mesial Distal Design

FIT MISFIT FIT MISFIT FIT MISFIT FIT MISFIT

Design A 7 1 5 3 7 1 7 1

Design B 5 3 8 0 6 2 7 1

Design C 8 0 4 4 6 2 8 0

P=0.122, NS p=0.073, NS p=0.777, NS p=0.580, NS STEREOMICROSCOPE

Buccal Lingual Mesial Distal Design FIT MISFIT FIT MISFIT FIT MISFIT FIT MISFIT

Design A 0 8 1 7 0 8 0 8

Design B 1 7 0 8 0 8 1 7

Design C 0 8 0 8 0 8 0 8

P=0.352, NS p=0.352, NS p=1.0000, NS p=0.352, NS

50

Table 9: Percentage of 288 sites with inadequate marginal fit as detected by ,

explorer, elastomeric disclosing media, and stereomicroscope

Technique N Percentage

Explorer 96/288 33.33%

Disclosing media 29/288 10.06%

Stereomicroscope 228/288 79.16%

MISFIT FIT

33.33%

66.67%

Graph 5: Percentage of Fit and Misfit sites in Explorer

MISFIT FIT

20.84%

79.16%

Graph 7: Percentage of Fit and Misfit sites in Stereomicroscope

MISFIT FIT

10.06%

89.94%

Graph 6: Percentage of Fit and Misfit sites in Elastomeric disclosing media

51

Table10: Results of stereomicroscopic evaluation of 288 marginal gap sites compared

to explorer using stereomicroscope as gold standard

Stereomicroscopic findings

+(MISFIT) -( FIT)

Total

Explorer findings

+(MISFIT)

-( FIT)

91

137

5

55

96

192

Total 228 60 288

Table 11: Results of stereomicroscopic evaluation of 288 marginal gap sites

compared to elastomeric disclosing media using stereomicroscope as gold standard

Stereomicroscopic findings

+(MISFIT) -( FIT) Total

Elastomeric disclosing

media

+(MISFIT)

-( FIT)

24

204

5

55

29

259

Total 228 60 288

52

Illustration 1:

SENSITIVITY can be calculated using statistical formula given by park43

Sensitivity = TP/TP+FN

Where, TP = True positive,

FN = False negative.

For explorer,

Sensitivity = 91/91+137

= 0.39

= 39%

For elastomeric disclosing media,


= 0.10

=10%

Illustration 2:

SPECIFICITY can be calculated using statistical formula given by park43

Specificity = TN/TN+FP

Where, TN = True negative,

FP = False positive.

For explorer,

Specificity = 55/55+5

= 0.91

= 91%

53

For elastomeric disclosing media,


= 0.82

= 82%

54

DISCUSSION

Several authors have emphasized that marginal accuracy and internal adaptations are

critical factors for clinical success of cast restoration. The relationship between rate of

failure and size of opening of margins for dental castings has not been established by

definitive, longitudinal, and clinical studies. However, there is general agreement that

it is desirable to have margins closed as much as possible to reduce width of cement

line. A recent study showed that thickness of cement layer may interact with other

factors to affect the speed of disintegration of dental cement. The relationship

between margin adaptation and periodontal health has been confirmed in experimental

animals and humans.

This study was designed to evaluate the relationship of marginal accuracy of cast

restorations to various tooth preparations. The three preparation designs evaluated in

this study are most commonly used in the clinical practice. Previous studies could not

come to an agreement as to which is the best finish line in terms of marginal

adaptation. Some studies concluded that feather edge and bevel finish lines provide

the best marginal seal19 while others suggested shoulder with oversized casting as best

finish line in terms of marginal adaptation.6 Therefore this study was undertaken to

determine the effect of these finish lines on the marginal adaptation of cast

restorations. In the current study it was determined that preparation designs assessed

had no statistically significant effects on the marginal accuracy of cast restorations.

This observation is consistent with that of the few recent studies.7, 16

A non precious copper based alloy NPG and phosphate bonded investment was used

in this study for the fabrication of castings. These materials have reported to provide

better marginal fit as per previous studies.

55

Christensen (1966) reported that when visible and invisible margins were evaluated

with an explorer the barely acceptable range was 2-51 µm with a mean of 21 µm and

34-119 µm with a mean of 74 µm respectively. However the results of present study

indicate that the most commonly used method i.e. explorer, for evaluating the fit of

castings may be even less reliable than reported. When margins are evaluated with an

explorer acceptance is more likely to be based on the size and character of overhangs

and ledges than on the actual size of opening of the margins.

The advantages of using an elastomeric disclosing media to aid in clinical assessment

of castings are well documented.8, 11 In this invitro study, it appears that these

materials did not significantly aid in detection of marginal gaps as compared to the

explorer. However the use of elastomeric disclosing media, in the assessment of the

internal fit of castings remains valuable.11 In clinical practice, where assessment of an

inter-proximal area may be more difficult with an explorer, the use of these materials

may further assist in marginal discrepancy detection. So, an elastomeric disclosing

media was used as one of the technique of clinical evaluation of marginal adaptation.

One of the disadvantage of using an elastomeric disclosing media was that it reduces

cement bond strength due to the presence of residual silicone film. This film can be

removed from the internal aspect of the casting using an organic solvent or by air

abrading using aluminium oxide. Likewise, the film can be removed from the tooth

with a gentle prophylaxis, prior to cementation to enhance the cement bond strength.30

In current study, the sensitivity of explorer and elastomeric disclosing media as

compared to stereomicroscope at 30 µm was 39% and 10% respectively. Higher

values of sensitivity for explorer technique as compared to elastomeric disclosing

media indicate that explore technique is more reliable as compared to elastomeric

56

disclosing media in detecting marginal gaps. However values of sensitivity for both

the techniques evaluated is considerably low, indicating that these techniques may not

be adequate to determine presence of marginal gaps of or less than 30 µm.

The specificity of the explorer and elastomeric disclosing media as compared to

stereomicroscope at 30 µm was 91% and 82% respectively. Higher values of

specificity for explorer technique as compared to elastomeric disclosing media

indicates that explorer technique is more reliable as compared elastomeric disclosing

media in detecting margins that are closely adapted to prepared tooth. Similar results

were found in previous study done by Jahangiri.41

The limitations of this study are that the assessments of marginal accuracies were not

performed intraorally and that the errors in fabrication and handling of dies and

castings are assumed to be minimal. Within these limitations, it appears that clinical

examination based on an explorer and the use of elastomeric materials may not

provide satisfactory accuracy needed for detection of marginal gap sizes of less than

or equal to 30 µm. A recent study has reported that clinical detection of marginal gap

size with similar sensitivity and specificity as stereomicroscope occurs at greater than

or equal to 124 µm.41

Although the stereomicroscope cannot be used to assess restorations intraorally, the

future development of an intraoral apparatus may be of value. However, the use of a

stereomicroscope as a supplement method for assessing castings on dies may provide

a higher degree of marginal gap detection prior to examination of these castings

intraorally. This instrument is easy to use and is not considered costly.

57

The software program used in this study was purpose of multiple measurements and

storage of images, and future image analysis. This software program is not necessary

for quality.

58

CONCLUSION

1. The preparation designs examined in this study did not significantly affect the

marginal adaptation and accuracy of the castings.

2. Commonly used clinical evaluation techniques i.e. explorer and elastomeric

disclosing media may be inadequate for assessments of marginal accuracy.

3. Explorer technique proved to be better aid in detection of marginal accuracy as

compared to elastomeric disclosing media.

4. At 30 µm explorer revealed 39% sensitivity and 91% specificity and elastomeric

disclosing media revealed 10.06% sensitivity and 82% specificity.

5. For better evaluation of marginal accuracy of the cast restorations, the routine use

of a stereomicroscope in the laboratory is indicated which provides a superior

quality control prior to examination of restorations intraorally.

Above mentioned conclusions are within the limitations of this study. The

assessments of marginal accuracies were not performed intraorally, so further

research is required to obtain a better insight of the methods to assess the marginal

adaptation of the cast restorations that can be used intraorally.

59

SUMMARY

The aim of this study was to assess the effect of preparation design on

marginal adaptation, as well as to assess sensitivity and specificity of clinical

evaluation of cast restoration marginal accuracy when compared to stereomicroscopy.

Three Ivorine molar teeth of different designs were prepared:

Design A- A complete crown preparation with a buccal shoulder (1mm wide)



Design C- A three-quarter crown preparation with proximal boxes and beveled

finish line.

Elastomeric impressions of each tooth were made using individual custom-

fabricated trays. Eight individual dies were fabricated of each design. A total of 24

dies were prepared. Wax patterns were fabricated on the dies using type II inlay wax

and casted using a non precious gold alloy. The casting procedures were standardized

by investing immediately after waxing.

Each casting underwent examination with an explorer, elastomeric disclosing

media, and a stereomicroscope. Twelve circumferential recordings were made of each

casting, three on each buccal, lingual, mesial and distal surface, marked with a groove

on original ivorine teeth and highlighted using a fine indelible marker, for a total of

288 examination sites.

A ranking of “fit” or “misfit” was given to each examination site after

assessment with explorer and elastomeric disclosing media. Stereomicroscopy at a

value less than or equal to 30 µm measurements was used as a gold standard to

evaluate the significance of different designs on marginal adaptation. Three sites for

each buccal, lingual, mesial, and distal surface were given an overall evaluation of

60

acceptable or unacceptable. A surface was raked fit where all 3 measurement points

on a surface were less than or equal to 30 µm using stereomicroscopy. If any of three

measurement points of a surface had a value of greater than 30 µm, that surface was

ranked as misfit.

The data obtained was subjected to statistical analysis using Chi-square tests

of independence and Kruskal-Wallis test. It was found that the preparation design

examined in this study did not significantly affect the marginal adaptation and

accuracy of the castings. Examination by explorer at 30 µm revealed 39% sensitivity

and 91% specificity. The elastomeric disclosing media had 10.06% sensitivity and

82% specificity at 30µm. Thus the commonly used clinical evaluation techniques like

explorer and elastomeric disclosing media were inadequate for assessments of

marginal accuracy.

For better evaluation of marginal adaptation of the cast restorations, the

routine use of a stereomicroscope in the laboratory is indicated which provides a

superior quality control prior to examination of restorations intraorally.

61

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STATISTICAL FORMULA

1) Mean: sum of all the observation and divided by total no of observations X = ∑ Xi / n Xi = value of each of each observation, n= No of observation. 2) Standard Deviation: root mean square S D = ∑ (x – x) 2 / n-1 X = Variable, x = Mean of x, n = No of observation. 3) Chi-Square Test (χ2- test) χ2 = ∑ (Observed frequencies - Expected frequencies)2/ Expected frequencies = ∑ (O - E) 2/ E O = Observed frequencies, E= Expected frequencies. 4) Sensitivity: (by Park’s formula) Sn = TP / (TP + FN) Where TP and FN are the number of true positive and false negative results, respectively. 5) Specificity: (by Park’s formula) Sp = TN / (TN + FP) Where TN and FP and the number of true negative and false positive results, respectively.

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