MARGINAL ADAPTATION AND MICROLEAKACE OF PROCEM ALLCERAM COPINGS - AN IN MTRO STUDY

Francine Élise Albert

A thesis submitted in conformity witb the requirements for the degree of Master of Science

Graduate Department of Prosthodoi~tics Faculty of Dentistry

University of Toronto

O Copyright by Francine Élise Albert (2001)

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Marginal Adaptation and Microleakage of Procera AlICeram Copings - an in vitro

s tudy . Francine E. Albert, Master of Science, Prosthodontics, Faculty of Dentistry, University of Toronto, 200 1.

This study sought to investigate the marginal adaptation and microleakage of Rocera

AllCeram copings (PAC) and porcelain-fused-to metal (PFM) copings with zinc

phosphate (ZnP0+ glass ionomer (GIC), resin modified glass ionomer (RrnGIC) and

resin (R) cements. PFM copings exhibited significantly less microleakage than PAC

copings. None of the coping margins cemented with ZnP04,58% GIC, 48% RmGIC and

65% in the R group demonstrated zero rnicroleakage. A significant difference between

PAC (548) and PFM (298) mean marginal adaptations was found. Specimens cemented

with Z n m cement showed significantly larger marginal gaps ( 5 4 ~ ) as compared to GIC

(40p), RmGIC (378) and R (378). PFM and PAC cooines orovided acceotable margins

and the use of R cernent resulted in the highest percentage of zero microlealcage scores.

A ma famiile:

Ce mémoire est dédié tout d'abord, à mes parents: Cécile et Louis-Philippe pour leurs

amour et support inconditionnel au fil des années. À ma soeur Suzanne au grand coeur et

Paul; mon frére Daniel, qui fut l'inspiration pour mon choix de carrière et Kilby, ainsi

qu'à ma soeur et éternelle CO-loc Natalie qui a procuré l'encouragement et l'humour

nécessaire pour réussir de longues études. Puis, à mes neveux et nièces: David, Sophie,

Daniel, Andrée et ma filleule Émilie, que j'aiment beaucoup. Sachez que ce travail

n'aurait pu être accompli sans vous.

Acknowledgements

1 would like to thank my CO-supervisors Drs. Omar El-MowaQ and George Zarb for their time spent supewising expenments and reviewing this manuscript. Your patience and guidance through this project was greatly appreciated.

1 am grateful to: Dr. Philipp Watson and Mr. Robert Chemecki for their technical support and assistance; Dr. Herenia Lawrence for help with statistical analyses; Lindberg- Homburger-Modent Dental Laboratones, Mr. Walter Maahre and Nobel Biocare for laboratory support; as well as Mrs. Janet DeWinter, Sharon Pike and Lori Mockler for assistance whenever needed.

I would also like to thank Mr. Tim Brown from 3M for the donation of impression matenal, Dr. Robert Carmichael for the loan of the parallel-a-prep device and Dr. Gerald Baker for the collection of extracted teeth.

I am most grateful to my colleagues, Drs. John Zarb, Nikolai Attard and Cecilia Dong for making these three years of graduate studies pleasurable. To Laura, Tony and Emily for their fkiendship and for showing me what Toronto has to offer and to Dr. Bruno Girard for his many years of encouragement and assistance as well as for CO-authonng the article which convinced me to pursue Prosthodontic graduate studies.

This study was supported in part by a gant fiom the Faculty of Dentistry Research Committee and by Nobel Biocare.

Table of contents

Abstract

Acknowledgements

List of figures

List of tables

List of abbreviations

Introduction

Section 1 : Overview

1.1 History of metal-ceramic crowns

1.2 History of all-ceramic crowns 1.2.1 Aluminous porcelains 1.2.2 Glass ceramics 1.2.3 Leucite-reinforced porcelains

1.3 Advantages of all-ceramic restorations

1.4 Disadvantages of all-cerarnic restorations

1.5 Clinical performance of porcelain-fused-to-metal crowns

1.6 Clinical performance of all-ceramic systerns 1 -6.1 In-Ceram crowns 1 -6.2 Dicor glass-ceramic crowns 1.6.3 IPS Empress crowns 1.6.4 Procera AllCeram crowns

1.7 in vitro testing of all-ceramic systems 1.7.1 Aesthetic potential 1.7.2 Strength 1.7.3 Marginal adaptation 1.7.4 Wear of opposing dentition 1.7.5 Biocompatibility

1.8 Procera AllCerarn crowns 1.8.1 Manufacturing process of Procera crowns

. . 11

i v

ix

xi

xii

Section 2: Marginal adaptation

2.1 Effect of finish line

2.2 Efkct of the marginal design of the coping 21

2.3 Effect of porcelain veneenng

2.4 Marginal adaptation and clinical acceptability 22

Section 3 : Microleakage

3.1 E ffect of thermocycling

Section 4: Correlation between microleakage and marginal adaptation 25

Section 5: Cements

5.1 Zinc phosphate cernent

5.2 Glass ionomer cernent 28 5.2.1 Setting reaction 29 5.2.2 Fluoride, itaconic acid and tartaric acid in the setting reaction 29 5.2.3 Water interaction 30 5.2.4 Bonding mechanism 30

5.3 Resin-modified-glass ionomer cernent 32

5.4 Resin cernent 34

Statement of the problem

Objectives

Hypotheses 37

Materials and methods 39

Section 6: Pilot study

6.1 Specimen collection and storage

6.2 Specimen preparation

6.3 Impressions

6.4 Die preparation

6.5 Scanning of Procera dies

6.6 Casting of porcelain-fused-to-metal copings

6.7 Porcelain cycling

6.8 Cementation

6.9 Thermocycling

6.10 Microleakage testing

6.1 1 Marginal adaptation

Section 7: Statistical analysis

7.1 Marginal adaptation

7.2 Microleakage

Section 8: Main study

Results

Section 9: Pilot study

9.1 Marginal adaptation of PAC and PFM copings

9.2 Microleakage of PAC and PFM copings

9.3 Correlation between microleakage and marginal adaptation

Section 10: Main study

10.1 Marginal adaptation of PAC and PFM copings 10.1.1 Crown type 10.1.2 Margin location 10.1.3 Cement type 10.1.4 Section location 10.1.5 Multiple regression mode1

1 0.2 Microleakage of PAC and PFM copings 10.2.1 Crown type 10.2.2 Margin location

vii

10.2.3 Cernent type 10.2.3A Zinc phosphate cernent 1 O.2.3B Glass ionomer cernent 1 0.2.3C Resin-modified-glass ionomer cernent 1 O.S.3D Resin cernent

10.2.4 Section location 10.2.5 Logistic regression

10.3 Correlation between microleakage and marginal adaptation

1 0.4 intra-observer variabili ty

Discussion

Section i 1 : Marginal adaptation

1 t . 1 Effect of crown type

1 1.2 Effect of finish line

1 1.3 Effect of the marginal design of the coping

1 1.4 EfTect of porcelain veneering

1 1.5 Effect of cement

Section 12: Microleakage

12.1 Effect of cernent 1 2.1.1 Bond to tooth structure 12.1.2 Water absorption and solubility 1 2.1.3 Dimensional changes

12.2 Effect of thermocycling

12.3 Microleakage at the coping and cernent interface

12.4 In vivo vs. in vitro microleakage testing

Section 1 3: Correlation between marginal adaptation and microleakage

Section 14: Future research

Conclusion

References

List of figures

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Pilot Studiv

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Red fùschin dye (pararosanilin) structural formula

Bonding mechanism of glass ionomer cement

Acid base reaction

Polymerization reaction

Matrix of resin-modified glass-ionomer cement containing both ionic and covalent crosslinks

Parallel-a-prep device allowing standardized preparations of the specimens

Procera Sandvik Scanner

Specimen distribution according to cernent sub-groups.

Crown to tooth diagram showing measurement location of marginal opening (MO).

Mean marginal adaptation of PAC and PFM copings according to crown and cernent type.

Mean marginal adaptation of PAC and PFM copings according to margin location.

Mean marginal adaptation of PAC and PFM copings according to section location.

Percentage of PAC and PFM coping margins showing score 4 microleakage according to cement type.

Percentage of PAC and PFM coping margins showing various microleakage scores according to margin location.

Percentage of PAC and PFM coping margins showing various microleakage scores according to section location.

Figure 16

Figure 16A

Figure 17

Figure 17A

Figure 18

Figure 19

Figure 19A

Figure 20

Figure 20A

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Mean marginal adaptation of PAC and PFM copings according to margin location (margin as the unit of measure n= 160).

Mean marginal adaptation of PAC and PFM copings (crown as the unit of measure n=40).

Mean marginal adaptation of PAC and PFM copings according to cernent type (margin as the unit of measure n=80).

Mean marginal adaptation of PAC and PFM copings according to cement type (crown as the unit of measure n-20).

Mean marginal adaptation of PAC and PFM copings according to 68 section location.

Percentage of PAC and PFM coping margins showing various 69 microleakage scores according to margin location (margin as the unit of measure n= 1 60).

Mean number of PAC and PFM margins exhibiting microlealcage 70 scores of 3 or 4.

Percentage of PAC and PFM coping rnargins showing various 7 1 microleakage scores according to cement type.

Mean nümber of PAC and PFM rnargins exhibiting score 3 or 4 microleakage according to cernent type.

Percentage of PAC and PFM coping margins cemented with zinc phosphate cement showing various microleakage scores.

Percentage of PAC and PFM coping margins cemented with glass ionomer cement showing various microleakage scores.

Percentage of PAC and PFM coping margins cemented with resin- 75 modified-glas ionomer cement showing various microleakage scores.

Percentage of PAC and PFM coping margins cemented with resin cernent showing various microleakage scores.

Percentage of PAC and PFM coping margins showing various microleakage scores according to section location.

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Procera coping specimen showing microleaicage at the cernent- coping interface.

Microleakage specimen of a PFM coping cemented with zinc phosphate cernent.

Microleakage specimen of a Procera coping cemented with zinc phosphate cernent.

Microleakage specimen of a PFM coping cemented with glass- ionomer cernent.

Microleakage specimen of a Procera coping cemented with glass ionorner cernent.

Microleakage specimen of a PFM coping cemented with resin- modified-glass ionomer cement.

Microleakage specimen of a Procera coping cemented with resin- modified-glass ionomer cernent.

Microleakage specimen of a PFM coping cemented with resin cernent.

Microleakage specimen of a Procera coping cemented with resin cernent.

List of Tables

Table 1 Current dental ceramics and methods of fabrication

Table 2 Translucency range of various core materials

Table 3 Marginal discrepancy of various crown systems

Table 4 Physical properties of luting cements

Table 5 The linear coefficient of thermal expansion of various materials.

Table 6 Composition of four types of cernent used.

Table 7 Simulated porcelain firings for PFM copings

Table 8

Table 9

Table 10

Table 11

Table 12

PAC

PFM

ZnPOd

GIC

RmGIC

HEMA

4-META

4-MET

Simulated porcelain firings for Procera copings

Material used for cementation procedure

Manufacturer's recommendation for cementation procedure for various cements.

Microleakage scale for the assessment of leakage at the dentin- cernent intedace.

Procera AllCerarn crown mean marginal adaptation values according to di fferent studies.

List of Abbreviations

Procera AlICerarn

Zinc phosphate

Glass-ionomer cernent

Resin-modified-glass-ionomer cernent

4-methacryloxyethyl trimellitate anhydride

4-methacryloxyethyl trimellitic acid

xii

Introduction

1 -0vewiew

The satisfactory restoration of teeth with fùll-coverage restorations poses several

problems for the clinician. Achieving the most esthetic result while, at the same time

satisfjmg functional demands are two such concerns. Porcelain-fused to metal (PFM)

crowns are generally indicated when esthetic demands are coupled with the need for

maximum strength (Vahidi, 1 99 1 ). These restorations are not, however, as esthetic as

their all-ceramic counterparts. As a result of this and due to the fact that an increasing

number of patients desire metal-free restorations, some clinicians prefer to present a

metal-fiee alternative for full-coverage crowns.

Dunng the past 20 years, several all-ceramic crown systerns have been developed and

introduced to the profession. Some of these systems have represented significant

innovations while others have been evolutionary versions of earlier cerarnic systems (Cho

1998). Al1 have been developed in an attempt to compensate for some inherent

deficiencies in metal-ceramic restorations.

1 .l History of metal-ceramic crowns

The introduction of the bonding of porcelain to gold alloys by Weinstein et al. in the

early 1960s was a pivotal breakthrough in dental esthetics. lt allowed gold frameworks

to be esthetically concealed by bonded porcelain (McLean 2001). The unique

characteristics of the metal bond, imparted to metal-ceramic restorations special

properties that include high tensile strength, fiacture toughness, resistance to Wear and

resistance to corrosion in the oral environment.

Two signifiant developments with metal-ceramic restorations in the past several years

have dramatically improved their esthetic potential. The first is the development of

techniques to build color internally within the ceramic veneer. The second improvement

has been the devdopment of numerous techniques for simplifjmg fabrication of al1

porcelain labial margins (Cho et al. 1998). Today it is accepted that very good esthetics

can be achieved with porcelain-fused-to-metal crowns.

1.2 History of aii-ceramic crowns

Land introduced the first porcelain jacket crown in 1886. He used a bumished platinum

foi1 to serve as a matnx for fùsing porcelain (Jones 1985). For many decades it was

considered the most aesthetic fùll coverage restoration available. In the 1960s, the need

for improved physical properties fùelled the development and introduction of new

ceramic matenals.

1.2.1 Aluminous porcelains

Few important advances occurred in dental cerarnics until McLean and Hughes

introduced alumina-reinforced dental porcelain in 1 965. In this system, the feldspathic

porcelain core is strengthened by 40-50% dispersed crystals of high-strength alumina

(Andersson & Odén, 1 993). The alumina crystals act as potential bbcrack-stoppers" since

for a crack to propagate, it must travel through each crystal in its path (McLean 1965).

The strength of this new reinforced porcelain was approximately double that of the

conventional feldspathic materials.

In 1983, the AllCeram (Cerestore) porcelain crown was introduced. This system employs

the lost wax technique and its core is reinforced with 70% alumina crystals. Claus first

described the HiCeram porcelain system in 1987. It consisted of a 40% alumina

reinforced core and was fabricated directly on a refiactory die. It was then veneered with

conventional feldspathic porcelain. HiCerarn was superseded by InCerarn which was

originally described by Sadoun (Sadoun 1998). This system is based on the fabrication

of a 99.56% aluminous core that is subsequently saturated by lanthanum glass. The core

is veneered with a ceramic material with aluminous oxide crystals scattered throughout

an amorphous vitreous matrix. In 1993, Andersson and Ocien developed the Procera

AliCeram crown through a cooperative effort between Nobel Biocare and Sandvik Hard

Matenals. The Procera AllCeram crown is composed of a coping of 99.9% densely

sintered high purity aluminum oxide veneered with dental porcelain (Oden et al. 1998).

This system employs cornputer-assisted design and computer-assisted machining (CAD-

CAM) technology to fabncate its coping which is then veneered with porcelain.

1.2.2 Glass ceramics

MacCulloch first described methods for making crowns in glass ceramic in 1968

(MacCulloch, 1968). His pioneering effort received very little recognition. In 1978, a

different glass cerarnic material was developed by Adair and Grossman and later released

to the dental community under the trade name Dicor (Adair and Grossman, 1982). This

castable glass ceramic restoration is fabricated using the lost-wax technique. The

ceramic is reinforced with fluorine-containing tetrasilicic mica crystals.

1.2.3 Leucite-reinforced porcelains

The IPS Empress system was introduced in the early 1990's by Wohlwend, in an attempt

to improve strength and toughness of ceramic materials. The fabrication methodology

involves a lost-wax investment technology and injection moulding of a leucite reinforced

glass cerarnic (Lehner and Scharer, 1992). The amount and dispersion of leucite crystals

is intended to improve the resistance of fracture. Table 1 lists contemporary dental al1

cerarnic systems and their methods of fabrication.

Table 1: Current dental ceramics and methods of fabrication (Adapted from Attard and Dong, 2000)

1 Dicor 1 I . Y

1 Tetrasilicic mica 1 Lost wax ~ a t t e m techniaue

Metbod of fabrication S l i ~ casting:

Ceramic system In-Ceram

1.3 Advantages of ail-ceramic restorations

-One of the main advantages of all-ceramic restorations is optimum esthetics since there

is no metal show-through and there is also the potential for improved light transmission

in the cervical third (Cho 1998).

-Ceramics are regarded as biocompatible and inert matenals.

Rein forcement Alumina

IPS Empress Procera

I . I

Leucite Alumina

Lost wax pattern technique CADICAM

-Low plaque accumulation (Chan 1986), low thermal conductivity (Odén et al., 1998)

and a coefficient of thermal expansion similar to that of dentin have also been reported

(McLean 200 1 ).

-Another advantage is that densely sintered aluminum oxide and feldspathic porcelain

have a radiographie contrast similar to that of dentin. This makes it possible to

radiographically diagnose changes in the underlying tooth structure (Odén et al. 1998)

1.4 Disadvantages of all-ceramic restorations

-Ceramic materials are brittle, limited in their tensile strength and subject to time-

dependent stress failure which in most cases, limits their use to anterior teeth (Stnib &

Beschnidt, 1 998).

-Marginal adaptation is a matter of concern (Strub & Beschnidt, 1998). Almost al1

ceramic crowns have inferior marginal adaptation as compared to rnetal-ceramic crowns

(Cho et al. 1998).

-All-ceramic crowns require more tooth reduction and are less consemative than metal-

ceramic crowns. To provide sufficient thickness of ceramic material for strength and

aesthetics, a unifonn circumferential 1.5 mm reduction is recommended. Therefore,

more tooth structure is reduced axially h m the interproximal and lingual surfaces with

all-ceramic preparations than with metal-ceramic preparations (Cho et al. 1998).

-With all-ceramic crowns it is difficult to compensate for lack of an ideal tooth

preparation. Accessory retention grooves cannot be used with all-cerarnic systems

employing CAD-CAM technology (Lin et al. 1998).

-Al1 types of porcelains will cause accelerated attrition of the opposing dentition when in

gliding contact with naniral teeth (Monasky 1 97 1 ).

1.5 Clinical performance of porcelain-fused to metal crowns

Many studies have examined the longevity of porcefain-fused to metal crowns. Walton et

al. reported a relatively short period of service of 6.5 years for metal cerarnic crowns.

The primary causes of failure being caries, porcelain fiacture or poor esthetics (Walton et

al. 1986). Leernpoel et al. found that the survival rate of 1323 metal ceramic anterior

crowns was 95% at 5 years and 82% at 1 O years (Leempoel et al. 1985). For 20 1 1

premolar metal ceramic crowns, the survival rate at 5 years was 98% and 97% at 10

years. Most clinical studies on metal ceramic crowns suggest a maximum failure rate of

2.8-5 % at 5 years. Therefore, it seems prudent to suggest that the maximum allowable

failure rate criterion in evaluating all-ceramic systerns should be 5% at the five-year

foilow-up.

1.6 CIinical performance of all-cerarnic systems

Clinical studies are necessary to evaluate both efficacy and effectiveness of new dental

systems and/or materials. The following clinical evaluations of contemporary ail-ceramic

systems are dificult to compare as they are al1 done in various settings and employ

different research designs. Nonetheless, the available clinical trial results of In-Ceram,

Dicor, IPS Empress and Procera dl-ceramic systems are presented and appraised.

1.6.1 In-Ceram Crowns

Probster reported on the clinical performance of 95 (68 posterior and 28 anterior) In-

Ceram crown restorations luted with conventional cements. Eighteen patients were

recalled for clinical investigations at least once a year. A failure of a restoration was

defined as a fracture exposing prepared tooth substance or total loss of a restoration. In

the 56-month observation period, no total failure requiring replacement of a restoration

occurred. The veneer of a single molar crown tiactured while its cerarnic core remained

intact. With four crowns, marginal canes was observed after 2 to 4.5 years. This

prospective clinical study suggests that In-Ceram complete coverage restorations are

indicated for both anterior and posterior teeth (Probster 1996).

Similarly, Scotti et al. investigated 63 In-Ceram crowns in both dental school and private

practice settings. The study population consisted of 45 patients who were recalled at 3-

month intervals for the first 9 months and then biannually for the remainder of the 24 to

44 month study penod. Approximately 62% of the restorations were placed in the

posterior segment. One fiactured crown was reported (Scotti et al. 1995). These data

support other research validating the success of the In-Ceram system. The weakness of

these papers is their short to medium term observation periods which may be insufficient

to evaluate their ultimate clinical performance.

1.6.2 Dicor Class-Ceramic Crowns

Although it is highly aesthetic, studies have shown that Dicor crowns lack fracture

toughness and requires direct resin bonding if long-terni resistance to fracture is to be

achieved. in 1982, a database was initiated to prospectively assess certain risk factors

and their effect on the survival of Dicor full coverage restorations. One thousand four

hundred and forty-four Dicor restorations were placed in 4 17 patients in a private practice

setting, and were exarnined for up to 14.1 years. The patients were recalled every 6

months and the status of the restorations evaluated and recorded according to the study's

proposed criteria. A restoration was considered to be a failure if it exhibited a fiacture

that necessitated that the restoration be remade. Overall survival of the crowns was

determined and the effect of various clinical parameters was evaluated. Within the

limitations of the report's design, the probability of survival of an acid-etched Dicor

crown for the 14.1 -year observation penod in male subjects was 7 1 % and 75% for female

subjects. In general, there were 180 (1 2.4%) failures recorded out of the 1444 units

placed (Malament and Socransky, 1999). The authors concluded that Dicor crowns could

survive successfully over time with certain reservations

In the same way, Kelsey ' al. prospectively evaluated the Cyear clinical performance of

Dicor restoration in the posterior segments. One hundred and one crowns were placed in

61 molar and 40 premolar teeth using resin cement. Three restorations failed after 2

years, while by the end of the Cyear observation period, 15 failed. Thirteen of these

failures were molar crowns (Kelsey et al. 1995).

These studies have shown that the primary disadvantage of the Dicor system is its

reduced flexural strength. Unfortunately, the data on this type of crown was only

recently available, long after the system was introduced and was a commercial failure.

The Dicor crown has virtually disappeared from the scene and the Dicor systern is mostly

being used for the fabrication of inlays because the problem of stress cracking has not yet

been solved (McLean 200 1).

1.6.3 IPS Empress Crowns

There are few studies dealing with the dinical performance of Ernpress all-ceramic

crowns. Sjogren et al. reported on 1 10 Empress crowns, placed in 29 patients who visited

a general practice on a regular basis. The restorations were also evaluated according to

the California Dental Association quality evaluation system. AI1 crowns were luted with

resin composite cement and the mean and median years in tiinction for the crowns were

3.6 and 3.9 years respectively. Ninety two percent of the restorations were rated

satisfactory and fractures were noted in 6% of the 110 crowns. Fractures were seen in

7% of the molars, 12% of the premolars and 2.7% of the incisors/canines (Sjogren 1999).

In a prospective three-year clinical trial, Sorensen et al. evaluated the longevity of 75

adhesively cemented IPS Empress full crowns. Sixty-three percent of the crowns were

placed on antenor teeth, 20% on premolars and 17% on first rnolars. The 33 subjects

were exarnined at baseline and recalled annually. At the three-year point, one molar

crown fiactured for a 1.3% failure rate (Sorensen et al. 1998). These short-term clinical

trials have indicated a higher failure rate when this system was used on posterior teeth.

Therefore, the risk of fracture when placing IPS Empress crowns on teeth that are likely

to be subjected to high stress levels is a matter of concem.

It would seem that a fatigue related process may be causing the restorations to fail in a

gradua1 fashion when submitted to high stress. A possible explanation of this

phenornenon was proposed in a study by Peters et al., in which it was noted that cracks

develop both externall y and interna1 1 y when a cerarnic restoration is functionally loaded.

The external cracks initiate at the point of opposing dentition contact, while the intemal

cracks start in areas of intemal line angles, such as an axio-pulpal ones. Restoration

failure will be delayed until these cracks propagate and eventually coalesce (Peters et al.

1993).

1.6.4 Procera AIICeram crowns

The Procera A11Ceram system is indicated for manufacturing all-cerarnic crowns for

single-tooth restorations in the anterior and posterior regions. In addition, it is possible to

create metal-fiee superstmctures for implant systems (Ottle et al. 2000).

Long-term clinical trial data supporting the efficacy of Procera AllCerarn crowns is

limited to a prospective five-year clinical evaluation (Odén et al. 1998). One hundred

fùll-coverage restorations were fabncated for 58 patients. Eighty-three percent of the

crowns were on premolars and molars while 17% were on incisors and canines. The

crowns were examined at baseline and once a year during the 5 years that followed. The

restorations were evaluated at each appointment using California Dental Association

quality assessment system. Of the 97 crowns remaining in the study after 5 years, 3

crowns had experienced a fracture through the veneering porcelain and the aluminum

oxide coping matenal. Two additional crowns were replaced as a result of fiacture of

only the veneering porcelain. One crown was replaced as a result of recurrent caries.

More specifically, 7% of molar restorations and 4% of premolar crowns failed while none

of the crowns on anterior teeth failed. Ninety-one of the remaining 97 crowns were

ranked as either excellent or acceptable for surfaçe/colour, anatornic form and marginal

integrity. Once again, this all-ceramic system showed a higher failure rate on posterior

teeth. It has been suggested that with Our current technique, it is impossible to produce

ceramic restorations that are fiee of microscopie defects known as Griffith's flaws

(McLean 1987). Such flaws will propagate and will undergo static fatigue (White et al.

1995).

It is clear that there is a lack of compelling information From carefully performed clinical

trials with large numbers of units and subjects, explicit inclusion and exclusion criteria,

specific rneasurernent critena and outcome deteminants, and prolonged periods of

recording at predetermined stages by calibrated examiners. The clinical trials that have

been conducted indicate that most available systems have high failure rates when used on

posterior teeth. Given that the primary indication for an all-ceramic restoration is high-

aesthetic demand, and that this is rarely a problem with posterior restorations, it is

suggested that metal-ceramic crowns will continue to be placed on posterior teeth.

1.7 In vitro testing of all-ceramic systems

Every new dental material and procedure must be evaluated against the standards of care

currently available to the profession at the time of its introduction. Certain requirements

with regard to the aesthetic qualities, strength, marginal integrity, Wear characteristics and

biocompatibility are essential for any crown system to be successfùl. In the following

sections, relevant irt vitro studies of various all-ceramic systems are presented in

comparison with the current standard in full coverage restorations i.e. the porcelain-tùsed

to metal crown.

1.7.1 Aesthetic potential

In general, al1 the ceramic systems discussed can obtain a high standard of aesthetics in

cornparison with their metal-ceramic counterpart. These aesthetic qualities are Iinked to

the all-ceramic crown's fabrication. Sorne systems contain a core that rnay Vary fiom

opaque to serni-translucent, veneered with porcelains that are compatible with the core

material. The veneering porcelains impart lifelike characterizations to the restoration.

By layenng the veneenng porcelains, intrinsic shadings can be accomplished, imparting

depth and beneficial light scattering optical properties. Ceramic systems that fit this

category are listed in increasing core translucency in table 2. In general, the more

translucent the core, the more lifeljke the restoration, due to its enhanced light

transmission characteristics (Holloway and Miller 1997). In other ceramic systems, the

entire restoration is fabricated fiom the same rnatenal, ofien cast or pressed in a

refractory mould. The shading of these systems is accomplished by the application of

extrinsic stains that render the restoration lifeless. As a result, a variety of these systems

(IPS Empress and Dicor) now include veneering porcelains, which allow the matenal to

be used as a core.

Discolored tooth structure is a difficult aesthetic challenge. The core must be sufficiently

opaque to mask the discoloration and the overlying porcelain material rnust diffise the

opacity of the core. The Procera coping is semi-translucent and thus will not allow any

dark underlying dentin or restorative material to shine through while still matching the

translucency of the adjacent teeth (Odén 1997). To demonstrate this capability, a study

was initiated to evaluate the masking ability of the coping. Tooth preparation rnodels

were milled fiom white plaster and black graphite. The masking ability of the coping

was determined by measunng the reflectance of the copings placed on the models with a

colorimeter. No significant differences were found between the two types of models and

hence it was concluded that additional procedures to eliminate the influences of any dark

underlying materials were unnecessary (Odén 1997). Moreover, excellent color stability

has been reported for AllCeram veneering porcelain us& with the Procera system. No

clinically detectable color change was measured after 5 years (Attanasi et al. 1997).

When selecting an all-ceramic system, the inherent translucency of the ceramic materia:

and the shade of the prepared tooth are important factors that will impact on the aesthetic

outcome of the restoration. The evidence suggests that the Procera system combines

excellent masking ability as well as optimum aesthetics.

Table 2: Translucency range of various core materials (Adapted from HoiJoway and Miller 1997)

Least translucent - Most translucent Dicor Metal alloy

Hi-Ceram In-Ceram

IPS Empress Procera

1.7.2 Strength

While the need for aesthetic restorations has become predominant in recent years, the

requirement that such restorations provide a long-term clinical life span is also

paramount. The strengths of brittle matenals are usually measured in flexure (Zeng et al.

1996). In bending, tensile stress reaches a maximum on one surface and compressive

stress reaches a maximum on the opposite surface. Ceramics usually fail in tension

therefore bending tests provide information on tensile strength. There are numerous

studies examining the flexural strength of all-ceramic crowns. The literature has reported

ranges of 320-490 MPa for In-Ceram, 80- 1 50MPa for Dicor and 160- 180 MPa for IPS

Empress (Yoshinari and Derand 1994). The flexural strength of Procera AllCeram (60 1

Mpa +/- 73) is significantly higher than all-ceramic materials used in dentistry (Wagner

& Chu, 1996; Zeng et al., 1996).

1.7.3 Marginal Adaptation

Clinically acceptable marginal adaptation values for cast restorations, including metal-

ceramic crowns have been reported in the literature to be approximately 60 microns or

less (Gavelis et al. 198 1). On the other hand, studies o f al1 ceramic crown systems have

reported mean marginal openings of approxirnately 155 microns. Table 3 reports on the

marginal adaptation of various crown systems. These studies are difficult to compare

since the evaluation of the marginal discrepancy depends on several factors:

measurement of cemented or not-cernented crowns, storage time and treatment after

cementation, kind of abutment used for measurements, kind of microscope and

enlargement factor used for measurements as well as location of measurements

(Beschnidt and Stmb 1999). Moreover, marginal integrity may be more dependent upon

the ability of the clinician to provide a margin of optimum design and upon the ski11 of

the laboratory technician than the inherent accuracies of each system (Hotmes 1992).

Table 3: Marginal discrepancy of various crown systems

Reference

1

Weaver et al. 1991

Ferrari 1991 Abbate et al. 1989

Material

Porcelain facial PFM Dicor

Grey et al. 1993

Mean marginal discrepancy (pm)

59 57

Dicor Meta1 facial PFM Porcelain facial PFM Dicor

Sorensen et al. 1998 Omar 1987

1 Hung et al. 1990 1 Dicor 98

15-75 6 1 *26 57+24 65* 1 7

In Ceram PFM

I Beschnidt and Strub 1999

123*30 95A23

In Ceram copings PFM

24-67 (range) 76*2 1

In Ceram IPS Empress PFM

L

Sulaiman et al. 1997

60 62 64

Weaver et al. 1991

1.7.4 Wear of opposing dentition

Porcelain restorations that oppose natural

PFM IPS Empress

l

teeth can have serious

65 62*37

Focera Dicor

--

[ PFM

consequences

82*4 1 57 59

on the

Wear of enamel surfaces. Clinical

reproducible way, thus research has

evaluation of abrasion is difficult to measure in a

been limited to in-vitro studies. These studies are

flawed by confounding variables and are difficult to compare due to a lack of conformity

in rnethodology. Previous studies have shown that enamel Wear when opposed by

feldspathic porcelain is substantially greater than when opposed by gold restorative

materials (Mahalick et al. 1971). Krejci et al. reported that feldspathic porcelain wore

enarnel more than did pressed glass ceramic (Krejci. et al. 1993). A similar study

compared the enamel Wear against low-fusing AllCerarn porcelain (Procera system) with

the Wear against Cerarnco feldspathic porcelain and gold alloy (Hacker et al. 1996).

Significant differences in mean enamel Wear were found when abraded against gold

(9pm), Procera AllCeram (60pm) and Ceramco feldspathic porcelain (230pm).

Consequently, it would seem that Procera AllCeram porcelain is more compatible with

enarnel than feldspathic porcelain. However, the authors overlooked the incorporation of

a control (enamel abraded by enamel) in their experiment which might have shown that

Procera veneering porcelain was kinder to the opposing dentition than enamel itself.

Ratledge et al. demonstrated that glazed Vitadur porcelain was rnost destructive to dental

enamel, closely followed by unglazed IPS Empress ceramic and enamel (control)

(Ratledge 1 994).

It would seem that Procera AllCeram veneering porcelain offers a clear advantage of less

enarnel Wear than other feldspathic type porcelains. However, in vivo evaluations are

needed to determine whether these findings are consistent with what happens in the oral

environment.

1.7.5 Biocompatibility

It has ofien been stated that certain all-ceramic crowns are more biocompatible than their

rnetal-ceramic counterparts. In general, side-effects fiom dental materials are a minor

problem. In prosthodontics, the incidence of adverse reactions is approximately 1:4ûû

and it is estimated that about 30% of these incidences are related to base-metal alloys for

removable partial dentures and to noble/gold based alloys for porcelain-fùsed-to-metal

restorations (Hensten-Pettersen 1992). Palladium based alloys have been associated with

cases of stomatitis and oral lichenoid reactions. Moreover, palladium allergies occur

frequently in individuais who are sensitive to nickel (Wataha and Hanks 1996).

In general, dental cerarnics are considered to be the most inert of al1 dental materials used

for dental restorations. The toxicity potential of al1 dental ceramics is believed to be

negligible because of their excellent chernical durability and low Wear rates of opposing

materials during function (Anusavice 1992). Aluminous oxide in particular, has been

used for various clinical applications. The most common has been as socket and bal1 in

hip joint replacements (Andersson 1993). The overall safety and effectiveness of dental

ceramics has been well-accepted by the profession because of the freedom fiom adverse

effects of feldspathic porcelains during this century. Consequently, cerarnic crowns may

be of use in treating patients with a documented metal allergy.

1.8 Procera AllCeram Crowns

Since the early 1960s, researchers have been seeking new ways of fabricating all-ceramic

restorations that possess the needed qualities of colour stability, strength, precision of fit,

favourable Wear characteristics and biocompatibility so that they may be placed in ali

regions of the dental arches. Additionally, these techniques must produce crowns that

consistently meet these qualities in a manner that is cost-effective for the patient, dentist

and laboratory. The Procera AllCerarn crown system seerns to be one such system that

embtaces the concept of CADKAM technology to fabricate dental restorations.

1.8.1 Manufacturing process of Procera crowns

The Procera AIlCerarn crown was introduced in Canada in 1997. The Procera system

consists of a computer-controlled design station in the dental laboratory that is joined

through a modem to a coping manufacturing plant in New Jersey for the North American

market or in Sweden. At the design station, a scanning device controlled by a persona1

computer maFs the surface of the die of the prepared tooth. Prior to the scanning, the die

is onented vertically in the die holder. A sapphire bal1 (2.5 mm diarneter) forms the tip

of the scanner probe that contacts the surface of the die as it rotates around a vertical axis.

Extremely light pressure of approximately 20 g maintains the probe in contact with the

die as it rotates.

As the platform rotates, one data point is collected at every degree around the 360-degree

circumference of the die. During each rotation of the die, the probe is automatically and

continuously elevated 200 microns by the computer and another scan line is read until the

entire surface contour of the die has been mapped, thus descnbing the tooth through the

use of approximately 50,000 measured values. The maximum shape-related error of the

Procera scanner is 10 microns (Persson et al. 1995, Andersson et al. 1998).

When scanning is completed, the data are viewed on the computer screen and two-

dimensional plots are visualized and rotated by 5 degrees around the vertical axis of the

die. Marking of the finish line on the two-dimensional plots is the next step to be

completed during the design of the coping. The margin of the preparation is enlarged and

at every 5 degrees, the finish line is marked by the operator and the software interpolates

the segment between the marks. When the margin of the preparation has been defined, it

is saved to a computer file for desigriing the coping. Then, the thickness of the coping

and the emergence angle are established. The relief space for the luting agent is

automatically established by a computer algorithm. When the design of the coping has

been completed, the file is saved in the computer and is ready for transmission via

modem to the production station.

Once the information is received, the Procera all-cerarnic copings are manufactured by

compacting high-purity alumina powder (A1203 99.9%) against enlarged models of the

tooth preparation. The tooth preparation models are made with an enlarging copy milling

machine; the enlargement is calculated to corn pensate for the shrinkage associated with

the sintering of the compacted powder. The compacted copings are adjusted along the

preparation border and sintered at 1550 degrees Celsius for 1 hour (McLean, 2001).

During firing of alumina, welding occurs at points of contact between adjacent oxide

particles, giving nse to a lensing effect (partial fusion) that normally occurs in sintering

processes. Migration of atoms then leads to growth of the lens areas and reduction of

porosity. During sintering, the shift in grain boundaries results in the formation of a

closely interlocking crystalline structure of considerable strength (McLean and Hughes,

1965). A dense crystalline structure with an average grain size of 4 microns results. The

coping is examined for quality control and sent by mail to the dental laboratory where the

cerarnist finalizes the restoration by addition of veneering porcelain to create appropriate

anatomic form and aesthetic qualities.

2. Marginal Ada~tation

Marginal adaptation is an important criterion used in the clinical evaluation of fixed

restorations. The presence of marginal discrepancies in the restoration exposes the luting

agent to the oral environment (Sulaiman et al. 1997) and may lead to increased

dissolution of the cementing medium (Boening et al. 2000), recurrent caries (Abbate et al.

1989) and loosening of the cast restoration (Jacobs et al. 199 1). In vivo studies have

provided evidence that a large marginal discrepancy in a fixed restoration correlates with

increased plaque retention and reduced gingival health as indicated by higher plaque

index, elevated gingival index and increased pocket depth (Si lness 1 970, Valderhaug

1976, Janenko and Smales 1979). Misfits in all-ceramic crowns can also affect fiacture

stength (Tuntiprawon 1995). Many factors affect the marginal adaptation of a crown

such as the preparation dimensions, type of finish line, type and cernent viscosity,

location of cernent application (Assif et al. 1987), physico-chernical interactions between

cernent, tooth structure and coping, moisture, temperature, relief of the intemal crown

surface, marginal design of coping, crown type and seating force (White 1995, Gavelis et

al. 198 1 ).

2.1 Effect of fmish line

When a crown is cemented, the axial wall of the preparation approaches the axial wall of

the intemal crown surface and the escape path for the cernent decreases, causing the

hydrostatic pressure within the crown to increase. Several authors have predicted

marginal closures based on mathematical analysis of crown margin geometry. Rosner

proposed the placement of a bevel on 90-degree shoulden to reduce marginal

discrepancies (Rosner 1963). Theoretically, as the bevel becomes parallel with the path

of insertion, the distance between the beveled tooth surface and the restoration should

approach zero. This theory of gap reduction has since been discounted since the bevel

reduces the horizontal gap by partially converting it to a vertical one equal to the distance

by which the restoration fails to seat completely at the occlusal surface.

Other authors have shown that certain finish lines apparently facilitate the escape of

cernent early in the cementation process. Lofstrom and Barakat showed that a shoulder

margin exhibited larger mean marginal openings and increased microleakage than a

charn fer margin (Lofstrom & Barakat 1 989). It appears that, contradictory evidence

exists in the literature as to the effect of finish line on marginal adaptation.

2.2 Effect of the marginal design of the coping

The value of a bulk of metal at the margin of PFM crowns to minimize distortion during

porcelain fusion has been established (Faucher et al. 1980). Conversely, a significant

disadvantage of this bulk is the potentially visible metal that may be unacceptable to

many patients. This concem has lead to the development of crown designs that minimize

the appearance of metal collars. Belser exarnined the comparative fit in vivo of three

types of PFM crown margins: the beveled metal margin, metal butt margin and the

porcelain butt margin. There was no significant difference in marginal openings among

the three types of margins either before of after cementation (Belser 1985). In a similar

study, Strating et al. found that porcelain-füsed-to-metal restorations with porcelain butt

rnargins had significantly larger mean marginal opening than metal butt rnargins and 0.5

mm metal collar margins (Strating et al. 198 1).

2.3 Effect of porcelain veneering

Boening et al. examined the accuracy of fit of Procera copings both before and afier the

application of ceramic veneer (Boening et al. 1992). No statistical differences were

found before the porcelain was applied or after firing the ceramic veneer. In a related

study, Valderrama et al. compared the marginal fit of Procera crowns and metal cerarnic

crowns (Valderrama et al. 1995). No statistically signifiant difference in the marginal fit

either before or after the application of the porcelain veneer was found. The marginal

opening of al1 crowns was 50 microns or less.

2.4 Marginal adaptation and clinical acceptability

There is no general agreement as to what constitutes a biologically acceptable margin

(Alkumm et al. 1992). An American Dental Association specification States that the

luting cernent film thickness for a crown restoration should be no more than 25 microns

using a type 1 luting agent or 40 microns with a type II luting agent. Marginal fit of

restorations that range fiom 25 to 40 microns has been suggested as a clinical goal, but

marginal openings in the range of these dimensions are seldom achieved clinically.

3. Microleakaee

Microleakage is defined as the passage of fluids, bacteria, molecules or ions between a

restorative material and a tooth (Wendt 1992). Microleakage at the margins of crowns

may be a cause of failure of these restorations. The ingress of fluids and microorganisms

may lead to staining at the restoration-tooth interface, pulpal imtation and, in the long

term, dissolution of the cernent and development of secondary caries (Patel et al. 1997).

Microleakage detection tests play an important r d e in dental research and enable

investigators to assess the ability of restorative matenals and cements to seal the

restoratiodtooth interface. In the case of a crown, microleakage can be identified as the

linear penetration of dye from the margin of a coping inward along the tooth-cernent

interface (Shiflett & White 1997). Basic red fùschin dye (Pararosanilin, Ci9HisN3Al)

ionically bonds to tooth structure. This dye is an aromatic cornpound that includes aryl

rings which have delocalized electron systems (figure 1). These are responsible for the

absorption of electromagnetic radiation of varying wavelengths. Chromophores are

atomic configurations which c m alter the energy in delocalized systms. This alteration

results in the compound absorbing radiation from within the visible range of

electromagnetic radiation (Lillie 1977).

hH2 1

Fieure 1: Red fuschin dye (pararosanilin) structural formula

Causes of microleakage rnay include incongruity in the dimensional changes resulting

fiom disparity of the linear coefficients of thermal expansion of the different materials

involved (Tjan et al. 1980), lack of adaptation a d o r adhesion of the luting cernent to

tooth structure (Tjan and Chiu 1989), shrinkage of the cernent on setting, cernent

dissolution and perhaps mechanical failure of the cernent. Available cements vary

considerably in tems of solubility, strength and ability to adhere to tooth structure (see

table 4).

Table 4: Physical properties of luting cements (Rosenstiel et al. 1998, Katsuyarna et al. 1993, White 1992, Wilder 1996,3M data)

les's Zinc Phosvhate Fuji 1 Glass ionomer Resin modified glass ionomer C& B Metabond Resin

Solubility

High

Very low l 23

Low

Film thickness (pm) 28.1

3.1 Effect of thermocycling

Thermocycling is the irr vitro process of simulating the introduction of hot and cold food

substances in the mouth and as a result may allow variability of coefficients of thermal

expansion among tooth, cement and the restorative material to demonstrate its effect on

microleakage (Wendt et al. 1992). Variability in expansion and contraction among the

three may lead to breaking of the marginal seal between the restoration and the tooth,

particularly if the difference in coefficient of thermal expansion is great. The linear

Adhesion rn Pa)

-

22.5

Very low

1.3-3.7

26.3 11-14

coefficient of thermal expansion is defined as the change in length per unit length of the

material when its temperature is raised or lowered by one degree (Phillips, 1982). Some

linear coefficients of thermal expansions are represented in table 5. Hung et al. exarnined

the vertical marginal opening of porcelain-fused-to-metal crowns before and afier

cementation as well as after thermocycling. There were statistically significant

differences between al1 three test-conditions. It was concluded that marginal openings

increased after cementation and after thermocycling (Hung et al. 1990).

Table 5: The linear coefficient of thermal expansion of various materials.

4. Correlation behveen rnicroleakage and maryginal adaptation

Material

Gold Alumina Dentin Zinc phosphate (Fleck's) Glass ionomer (Fuji 1) Resin-modified-glass ionomer(Re1y x) Resin (Metabond)

The rate of dissolution has been related empirically to the degree of marginal opening. It

would seem that the larger the marginal gap and subsequent exposure of the luting

cernent to oral fluids, the more rapid is the rate of cernent dissolution (Cooper et al.

197 1). However, Fick's first law of diffision predicts that the rate of cernent migration

due to diffision is independent of the size of the gap. Moreover, the dnving forces

involved in the dissolution of the cernent is the diffision constant of the cernent and the

concentration gradient. Jacobs et al. investigated the rate of zinc phosphate solubility as

it relates to the degree of marginal opening. No statistically significant difference in

cernent solubility was found when the marginal openings were 25, 50 and 75 microns in

Coeflîcient of thermal expansion (xW4 /OC) 14.7 (Whitlock et al. 1 98 1 ) 7 (McLean and Hughes 1965) 1 1 (Craig 1993) 8 (Mizzy data) 10.7 (Katsuyama 1993) 1 1.5 (3M data) 8.4 (GC Corp data)

size (Jacobs et al. 199 1). Signifiant differences between luting agents in their ability to

prevent interfacial leakage along the tooth,cernent interface have been reported (White et

al. 1992).

S. Cements

The clinical success of fixed prostheses is heavily dependent on the cementation

procedure. Dental cements must act as barriers against microbial leakage, sealing the

interface between the tooth and restoration and holding them together through some form

of surface attachent. (Pameijer, 1994) This attachment rnay be mechanical, chernical or

a combination of both. An ideal adhesive should provide a durable bond between

dissimilar matenals, possess favourable compressive and tensile strengths, have suficient

fracture toughness to prevent dislodgment as a result of interfacial or cohesive failures, be

able to wet the tooth and the restoration, exhibit adequate film thickness and viscosity to

ensure complete seating, be resistant to disintegration in the oral fluids, be tissue

compatible and demonstrate adequate working and setting times (Diaz-Arnold, 1999).

There are five types of commercially available luting agents for the long-term

cementation of fixed prostheses and they include: Zinc phosphate, zinc polycarboxylate,

glass ionomer, resin-modi fied glass ionomer and resin cements. Pol ycarboxylate was not

included in this study as it is not widely used. The composition and characteristics of al1

other luting agents will be reviewed (table 6).

Table 6: Composition of four types of cement used.

Cements Fleck's Zinc

1 5% tanaric acid, water RelyX resin modified 1 Powder: fluoroaluminosilicate g l a s

Composition Powder: 90% zinc oxide, 8% MgO, 1.6%Si02

phosphate Fuji 1 glass ionomer

1 glass ionomer 1 Liquid: aqueous solution of a modified polyalkenoic acid, 1

Liquid: phosphoric acid, distilld water, hydrated alumina Powder: calcium fluoroaluminosilicate glass (29% SiOî, 16.6% Alto3, 34.3% CaF,, 9.8% AIP04, 5.3% AIF3, 5% Na3AlF6.)) Liquid: 47.5% (2: 1) polyacrylic acid/itaconic acid copolymer,

resin C & B Metabond

alcohol, water. 4-Meta catalyst: tri-n-butyl-borane

HEMA (2-hydroxyethylmethacrylate) Dentin Activator: citric acid, ferric chloride solution, polyvinyl

1 1 Base: methyl methacrylate 1 1 Powder: Poly ethyl methacrylate

5.1 Zinc phosphate cernent

Zinc phosphate cernent has been in use for more than ninety years (Arnes, 1892). A

typical formulation of a zinc phosphate cernent powder and liquid is shown in table 6.

The principal ingredient in the powder is zinc oxide. Magnesium oxide is added to

reduce the temperature of the calcination process, while the silicon dioxide is an inactive

filler in the powder. The ingredients of the powder are heated together at temperatures

ranging fiom 1000- 1300 OC for 4-8 hours. This calcination results in a sintered mass.

The mass is then ground and pulverized to a fine powder. The liquid is produced by

adding aluminum to phosphoric acid. The partial neutralization of the phosphoric acid by

the aluminum buffers the reactivity of the liquid. This reduced rate of reaction aids in

establishing a smooth, nongranular, workable cernent mass during the mixing procedure.

The setting time for the mixed cernent is modified by the proper dilution of the

phosphoric acid with water. Although phosphoric acid is very soluble, it is a weak acid

and the molecules in a concentrated solution dissociate to only a lirnited degree. If the

acid is diluted, increased dissociation results. The greater dissociation provides a better

chance of the acid to react with other matenals.

The surface of the alkaline powder is dissolved by the acid liquid, resulting in an

exothexmic reaction. The set zinc phosphate cernent is essentially a hydrated arnorphous

network of zinc phosphate that surrounds incompletely dissolved particles of zinc oxide.

Zinc phosphate is generally used with varnish pretreatment of dentine. Moreover, it does

not chemically bond to any substrate and provides a retentive seal by mechanical means

only. Previous studies have shown signifiant linear penetration of dye fiom the external

margin along the tooth-restoration interface (White 1994). Microleakage, aggravateci by

degradation in oral fluids and an initial low setting pH may affect its biocompatibility in

clinical use (Phillips 1987). However, the proven reliability of this cernent validates its

use in long-term lutinç of well-fitting prostheses (Diaz-Arnold 1999).

5.2 Glass ionomer cernent

The first glass ionomer cernent was developed by Wilson and Kent (Wilson & Kent

1972). It can be defined as a water-based material that hardens following an acid-base

reaction between basic fluoroaluminosilicate glass powder and an aqueous solution of

polyacids. The end result is an interpenetrating network of inorganic and organic

components forming a matrix in which particles of unreacted glass are embedded

(Nicholson 1998).

5.2.1 Setting reaction

The setting reaction of glass ionomer cernent is quite complicated and moreover, not fùlly

understood. When the powder and liquid are mixed, the powder being basic readily

reacts with the high-molecular acids that make up the liquid. The first stage of the

reaction is the ionization of the carboxyl radical (COOH) to COO- (carboxylate ion) and

H+. The H+ ion acts first on the surface of the glass particles. The calcium (caZ') and

aluminum (A13-t) are released into the liquid phase by the H+ attack on the glass surface.

The H+ ion then penetrates again into the structure, and the A13+ ion is dissolved away.

The aluminosilicate glass is broken down into silicic acid (H4Si04). This silicic acid

slowly causes a condensation reaction by means of its OH radical and becomes a porous

silica gel. Insoluble polyacrylate precipitate in the matrix and as it hardens, hydration

proceeds and a highly hydrated gel is formed (Katsuyama et al. 1993).

5.2.2 Fluoride, itaconic acid and tartaric acid in the setting reaction

The presence of fluonde contributes to the formation of complex bodies with metallic

ions released into the liquid. It becomes C ~ F ' and Al F ~ ' and delays the bonding of the

positive ions with either polyacrylic acid to fotm polyacrylate or with the COO- in the

copolyrner chains. The process of gelation is slowed and working time can thus be

lengthened. The formation of complex bodies quiclcens the release of the hydrogen ion,

lowering the pH of the paste. The gelation process, which depends on the pH is also

slowed.

Fluoride is thought to cause an elevation in the acid resistance of the surrounding tooth

structure. The hydrogen radical of the hydroxyapatite is displaced by fluoride, and

fluoroapati te is formed decreasing solubility toward acid and promoting recalcification

(Swartz et al. 1984). However, the small quantity of cernent at the margin may not have

any significant therapeutic value as a cariostatic agent (Christensen 1990).

The itaconic acid reduces the viscosity of the liquid and inhibits gelation caused by

intermolecular hydrogen bonding. Tartaric acid is a stronger acid than pol yacrylic acid

and it facilitates the extraction of ions from the g l a s powder. It improves the handling

properties by extending the working time of the cernent (Nicholson 1998).

5.2.3 Water interaction

The cernent is readily affected by water after the initial condensation. There are fluonde

and metallic ions in the cernent at this initial stage which have not yet reacted with

polyacrylic acid, as well as ions which are in the process of reacting with polyacrylic

acid. Once there is contact with water, the above are liquidated and the formation of a

strong matnx is prevented. As a result, the cernent weakens and whitens. The Na+ ion

becomes only sodium polyacrylate, a viscous substance and does not become a gel.

5.2.4 Bonding mechanism

The metaliic ions (M"), as well as the organic matter such as the carboxyl radical, the

carbonyl radical, amino radical and imino radical in the collagen form hydrogen bonds to

the carboxyl radical in the cernent paste, or bonding occurs by the cross-linking reaction

of the charged ions, and as a result bond strength increases.

Fieure 2: Bonding mechanism of glass ionomer cernent (Philips: Skinner's Science

of Dental Materials)

Glass ionomers possess several advantages compared to the resin composite, zinc

phosphate and other dental cements. Glass ionomers have an anticariogenic potential

produced by incorporated fluorine (Ten Cate et al. 1995), good biocompatibility, good

chernical adhesion to the tooth structure, well-balanced physical properties and good

handling characteristics. Several studies have reported decreased microleakage over non-

adhesive type cements (White et al. 1995) as well as improved seating of cast restorations

due to a low film thickness and viscosity (Oilo 1986) (table 4). However, early

exposure to water significantly decreases the hardness of the cement and if the marginal

adaptation of a restoration is poor, water sorption and dissolution may result in

dislodgment of the restoration.

5.3 Resin-modified-glass ionomer cernent

The introduction of resin-modified versions of glass ionomer cement represent an attempt

to combine the most advantageous properties of resins and g l a s ionomers. The term

resin-modified-glass-ionomers is the name given to those matetials that lead to the

formation of a metal polyacrylate salt and a polymer.

The setting reaction of resin-modified glass ionomer cernent is a dual mechanism. The

first reaction is the normal glass ionomer cernent acid-base reaction (figure 3). The

second is a free-radical polymerisation process similar to that usai in composite resins

(figure 4). The initial set is the result of polymensation of HEMA and not the

characteristic acid-base reaction of glass ionomer cements. The acid-base reaction serves

only to harden and strengthen the already formed polymer matrix (Wilson 1990). The set

cement has two interpenetrating matrices i.e. the ionic matrix fiom the acid-base reaction

and the polymerization matrix fiom the fiee radical reaction (figure 5).

Figure 3: Acid base reaction (Adapted from Wilson 1990)

I 1 ca2+

I =HZ I CH2

I =HZ

CH-COOH CH-COO- F- - I

OOC-CH I Calcium I I

Aluminosilicate I ----------------> =HZ

I CH-COOH glass CH-COO- F- - 1

OOC-CH I I I

Poly(acry1ic acid) Ca, Al polysalt hydrogel

Fieure 4: Polymerization reaction

Fieure 5: Matrix of resin-modified glass-ionomer cement containing both ionic and covalent crosslinks.

CHZ CH2 I C t i C 0 0 - M*+ - I

OOC-CH I 1

These cements have properties similar to glass ionomer cements i.e. adhesion to dentin,

their fluoride release pattern and low film thickness. However, they are more resistant to

water attack during setting because of the formation of an organic matrix and are less

soluble than glass ionomers (Sidhu and Watson 1995).

A significant disadvantage of these cements is the hydrophilic nature of polyHEMA

which resul ts in increased water sorption and subsequent plastici ty and h ygroscopic

expansion. Potential for substantial dimensional change contraindicates their use with

all-ceramic feldspat hic- type restorations. Resin-modi fied glass ionomers also present

concems regarding biocompatibility due to the presence of free monomer in the liquid.

Monomers are toxic and HEMA is no exception (Wilson 1990).

5.4 Resin cernent

Resin cernents polymerize through chemically initiated mechanisms. This involves

penetration of hydrophilic monomers through a collagen layer overlying partially

demineralized apatite of etched dentin. Dentin adhesion is obtained by infiltration of

resin primers into conditioned dentin, producing a micromechanical interlock with

partially demineralized dentin, through formation of a hybrid layer o r resin interdifision

zone. The luting procedure requires many steps. First an acid is applied to remove the

smear layer, open and widen tubules and dernineralize the top 2-5 microns of dentin. The

acid dissolves and extracts the apatite minera1 phase that nonnally covei the collagen

fibers of the dentin matrix and opens 20-30 nm channels around the collagen fibers.

These charnels provide an opportunity to achieve mechanical retention of subsequently

placed hydrophilic monomers (Vargas 1 997).

Leung and Morris exarnined the chemical interactions between 4-META and bovine

enarnel through the use of Raman spectroscopy (Leung and Moms 1995). The Raman

spectra showed that the 4-META molecules in monomer solution are mostly hydrolysed

into 4-MET molecules. They concluded that the ionic formation between 4-MET and

dental substrates is not likely instantaneous. In fact the rate of such a reaction is probably

too slow relative to that of polyrnerization of the CO-monomers to be important under

clinical conditions. The function of the 4-MET in the resin appears, therefore, to be

wetting of the tooth surface through hydrogen bonding, which then allows

methymethacrylate monomers to d i f i s e and penetrate deeper through the surfaces. The

primary bonding mechanism of this system is more likely due to a micro-mechanical

locking mechanism.

When resinous cements are used with a total acid-etch procedure, the resin film of

cement may redistribute stresses and increase the fiacture resistance of cerarnic materials

(McLean 2001). Moreover, 4-META resins show strong adhesion as a result of chemical

interaction of the resin with an oxide layer on the metal surface. A major advantage of

resin cements is that they are virtually insoluble in the oral environment. However, the

ability to seat restorations with resin cements has been investigated and in some

situations, cernent film thickness has been found to be greater than other classes of

cements (White 1993).

Statement of the problem

Metal-ceramic crowns have been used as hl 1-coverage res torations for several decades.

Recently, the manufacturers of Procera AilCeram crowns (PAC) have suggested that this

type of all-cerarnic restoration could be used in lieu of the conventional PFM crown.

However, an appreciable arnount of evidence suggests that all-ceramic crowns exhibit

inferior marginal integrity compared to metal-ceramic crowns (Stnib & Beschnidt, 1998,

Cho et al. 1998). It would also seem that the larger the marginal gap and subsequent

exposure of the luting agent to oral fluids, the larger the extent of microleakage. Many

authors have stated that the degree of microleakage is largely due to significant

differences in solubility, strength and ability to adhere to tooth structure of various luting

agents (White et al. 1992, Tjan and Chiu 1989). The aim of this study is to examine the in

vitro marginal adaptation and microleakage of Procera AllCeram copings using the

porcelain-fused to metal coping as a control, when different cementing media are used

i.e. zinc phosphate, glass ionorner, resin-modified-glass ionomer and resin cements.

Hence we wished to determine the following:

1) Do Procera AllCeram copings exhibit inferior marginal adaptation values

compared to PFM crowns?

2) 1s marginal adaptation correlated to microleakage?

3) Does cernent type affect marginal adaptation and microleakage?

Objectives

1. To examine the marginal adaptation of the Procera AllCeram (PAC) copings and

porcelain-fused-to-metal (PFM) copings cemented with zinc phosphate, glass

ionomer, resin-modified-glass ionomer or resin cements on extracted human

molars.

2. To examine the microleakage of the PAC copings and PFM copings cemented

with zinc phosphate, glass ionomer, resin-modified-glass ionomer or resin

cements on extracted human molars.

3. To determine if margin design has an efiect on the marginal adaptation and

microleakage of the copings.

4. To determine if there is a correlation between the marginal adaptation and the

microleakage of the specimens.

Hypotheses

1. There is no difference in the marginal adaptation of PAC copings and PFM

copings cemented with zinc phosphate, glass ionomer, resin-modified-glass

ionomer or resin cernent.

2. There is no difference in the microleakage of PAC copings and PFM copings

cemented with zinc phosphate, glass ionomer, resin-modified-glas ionomer or

resin cernent.

3. There is no difierence in marginal adaptation and microleakage between the labial

and lingual margins of the copings.

4. There is no correlation between marginal adaptation and microleakage of the

specimens.

Materials and methods

This study was preceded with a pilot study to identi% problem areas of the proposed

method of testing and to estimate the sample size required to achieve a 90% power and

5% significance.

6. Pilot study

6.1 Specimen collection and storage

Recently extracted intact third molars were collected from maxillofaciat surgeons and

stored in glass jars with distilled water as this storage solution does not seem to alter

dentin permeability (Goodis 1993). The teeth were scaled with periodontal curettes to

remove debris and sterilized by gamma radiation. The glass jar containing the specimens

was placed in a Cobalt 60 radiation chamber and exposed for 3.5 hours. The total

radiation dose used was 2.5 Mrad to eliminate microbes without altering the dentin

structure (White 1994, De Wald, 1997). The storage solution was changed every two

weeks and the teeth were stored at 4 degrees Celsius.

6.2 Specimen preparation

Al1 reductions were done using an apparatus to mount the specimens and a parallel-a-

prep device (figure 6) (Weissman Technology International). This device allowed

standardized preparations using a bur with a five-degree taper. Specifically, a Procera

chamfer bur (#806 314 298 534 018) for the Procera (PAC) group and a Brasseler

Figure 6: Parallel-a-prep device allowing stardardized preparation of the specimens

chamfer bur (#5856O 18) as well as a shoulder bur (#8847KR 0 18) for the porcelain-fûsed

-to-metal (PFM) group. Occlusal reductions were done with a football bur (MO6 3 14

257 534 023). Al1 reductions were done with a high-speed handpiece with airlwater

coolant.

The specimens (n=16) were divided into 2 groups. The PAC group (n=8) was submitted

to standardized tooth preparations consisting of a moderate chamfer (1.5 mm

circumferential and 2.0 mm occlusal reduction), with smooth contours and a rounded line

angles to produce the optimal precision of fit of the eventual coping (Andersson et al.

1998, Lin et al. 1998).

The PFM group (n=8) featured a shoulder preparation on the buccal (1 -5 mm) a chamfer

preparation (0.5 mm) on the lingual surface and a 2 mm occlusal reduction. The gingival

margins were placed apical to the cemento-enamel junction. Following the preparation,

the teeth were stored in distilled water and placed in an incubator at 37 degrees Celsius

(OC).

6.3 Impressions

The teeth were impressed with 3M Express regular and light body (lot #34-7039-1380-5

and 34-7039- 1379-7) polyvinylsiloxane matenal. The teeth were dried with an aidwater

syringe and light body impression material was injected ont0 the preparation. The

regular body polyvinylsiloxane material was placed in a disposable plastic cup and the

tooth was inserted into it. Non-latex gloves were used for this procedure as to ensure no

interference with the impression material's polymerization process.

6.4 Die preparation

The impressions were vaporized with a wetting agent (Debubblizer, Amencan Dental

Supply Inc. #D9 16) and poured in Die Keen stone (Canadian Medical Dental Gypsums

#99 12 1 848). This stone was mixed with Stalite special liquid solution (Buffalo Dental

Co. #80151) in a 20cc liquid to 100 grams of stone ratio as recomrnended by the

manufacturer. After a 4 hour setting time, the dies were trimmed using a IOx

magnification microscope and the finish lines were identified. One coat of die hardener

(Yeti dental lot #540-0060) approximately 6-9 microns thick (Campagni et al. 1986) was

applied to improve resistance to abrasion and hardness of the Stone dies.

6.5 Scanning of Procera dies

The dies for the Procera group were scanned by the Procera Sandvik Scanner (MOD 40:

10866; 1) (figure 7) which has a sapphire bal1 tip (2.5 mm diameter) that reads the die

shape by circular scanning. Tbe copings were ordered 0.6 mm thick to provide a sub-

structure with optimal support for the veneering porcelain. The copings were tried on the

dies and if they were found to rock. the die was rescamed and the coping remade. Two

copings were found to rock on the die and were reordered.

Fipure 7: Procera Sandvik Scanner

6.6 Casting of porcelain-fused-to-metal copings

Two coats of die spacer (Yeti dental lot#502-1000 yellow) approximately 25 microns

thick (Grajower et al. 1989) and die lubricant (Yeti Dental) was applied to the surface of

the dies. Studies have shown that die spacer creates space for the cernent film, relieves

the hydraulic pressure during the initial stage of cementation and facilitates distribution

of cernent with minimal friction, thus improving the marginal adaptation of cast crowns

(Wang et al. 1992). The wax-ups were done using the dipping technique and callipers

were used to ensure a uniform thickness of 0.6 mm. The labial margin design is a

disappearing metal margin while the lingual margin is a 1 mm metal collar. Casting

wax (Whaledent International lot#F-54B 80054) was used to refine the margins. The

wax-ups were sprued with Jelenko pre-fabricated sprues of 6, 8 and 10 gauge and

invested with a high-heat phosphate bonded material (Microfine Casting Investrnent)

according to the manufacturer's recommendations. The investment was burnt out and the

copings cast using a centrifuga1 casting machine. Jelenko microfine alloy (Olympia)

consisting of 5 1.5% Au, 38.5% Pd and 8.5% In was used. The copings were tried on the

dies and adjusted with a carbide bur for optimal fit with an indicator (Yeti Dental). If a

casting was found to have a problem that could not be corrected by a simple adjustrnent

such as rocking, it was recast. None of the specimens needed to be recast.

6.7 Porcelain cycling

Al1 specimens were submitted to simulated veneering porcelain application by cycling in

a porcelain fbmace (Jelenko Flagship VPF) The parameters used for the PFM copings are

listed in table 7 while as those used for the PAC copings are listed in table 8.

Table 7: Simulated porcelain firings for PFM copings

Preheat ('min"sec) Low t" ("C) Heat rate (OC/rnin)

/ Cool time / 10" ("sec)

Vaccuum level

Hi@ tO (OC) Hold time ('min "sec) Vent (OC)

Table 8: Simulated porcelain firings for PAC copings

Degassing 10"

704 56

O

1 038 O

No

Opaque 5'

500 75

Preheat ('minWsec) Low tO (OC)

Dentin 1 6'

600 55

-7 1

950 5'

949

Heat rate ("C/m i n) Vaccuum level

-73

940 40"

939

(cm/Hg) High tO ("C)

Liner 1 Dentin 1

55

-73

Hold time

('min "sec)

Vent (OC)

Dentin II 7 '

575

6 '

575

930

Cool time

("sec)

GIaze 4'

575

8 '

575 56

-73

1'

929

56

-73

920

30"

1 '

919

920

30"

900

1 '

919

3'

O

30" 30"

6.8 Cementation

The specimens were identified by a numencal code. The teeth were pumiced with a

prophylaxis cup mounted on a slow speed handpiece and nnsed with an air/water syringe

prior to cementation. Fit checker (GC Corp, Tokyo, Japan lot #090791) disclosing paste

was used to detect the presence of interference in the seating of the metal copings to the

specimens. White et al. have shown that the use of a silicone disclosing material

significantly improves the marginal fit of complete crowns (White et al. 199 1). Areas

preventing seating were relieved with a round diamond bur (Brasseler #5801 016). The

fitting surface of the metal copings was air-abraded with 80 microns aluminum oxide

powder (Jelenko) and cleaned with alcohol swabs. Intemal grinding of the alumina

copings was avoided as grinding procedures have been shown to affect the surface

texture and hence the strength of the material (Xu, 1994). The Procera and metal coping

groups were subdivided into 4 sub-groups of 2 specimens according to the cernent used

(figure 8, table 9). Groups P l and PFMl were cemented with Fleck's Zinc phosphate

cernent, Groups PZ and PFM2 were cernented with Fuji 1 glass ionomer cernent, while

groups P3 and PFM3 were cemented with Rely X resin-modified-glas ionomer cernent.

In addition, groups P4 and PFM4 were cemented with C & B Metabond resin cernent.

The cementation procedures were carried out according to the specific manufacturer's

recornmendations (table 10). A stylus with a 5 mm diarneter was placed on the tip of a

surveyor arm and was used to apply a constant 5 Kg load during the cementation setting

time. The teeth were placed in a holding device that was also used to assist in tooth

preparation. It has already been demonstrated that marginal adaptation is not improved

with a seating force in excess of 5 Kg (Jorgensen 1960, Weaver et al. 199 1 ). The excess

cernent was removed under magnification (Orascoptic loupes 2 . 6 ~ magnification).

Figure 8: Specimen distribution according to cement sub-groups.

~- , , \, \. PFM/PAC Copings

P4/PFM4 Resin

P l/PFM 1 Zinc phosphate

PZPFM2 Glass ionomer

~ 3 f f F M ~ Resin-modified- glass ionomer

Table 9: Material used for cementation procedure

Cements

Flec k's Zinc phosphate Fuji I glass ionomer

RelyX resin- modified- glass ionomer C & B Metabond resin

~anufacturer 1 Batch no.

powder OBX,

liquid OAK

GC Corporation lot.LO00 125 1,

PO002 15 1

~ a r k e l l ~iomatenals,

Farmingdale, NY

powder lot# 60502,

Base: TG3,

Catalyst: VG6 1,

Dentin activator:

5381/5373

Table 10: Manufacturer's recommendation for cementation procedure for various cements.

Cements Fleck's Zinc phosphate

Fuji 1 glass ionomer

RelyX resin- modified-glass ionomer

Instructions Powder: 0.8 g, Liquid: 0.3 cc Mixing time: 2 minutes Working time: 3.5 minutes Setting time: 10 minutes Powder: 1.8g Liquid: 1 .O g Mixing time: 30 seconds Working time: 1.5 minutes Setting time: 8 minutes PowderAiquid ratio 1.6: 1 by weight Mixing time: 30seconds Working time: 2.5 minutes

C & B

1 Setting time: 10 minutes 1

Setting time: 10 minutes Powder/base/catalyst ratio: 2 scoops: 2cc: I cc

Metabond resin

6.9 Thermocycling

Mixing time: 10 seconds Working time: 2 minutes

The teeth were stored in distilled water at 37 OC for 24 hours pnor to thermal cycling

according to the ISO (International Organization for Standardization) recommendations.

The specimens were submitted to 500 thennocycles in water between 5°C and 55°C. The

exposure to each bath was 30s and the transfer time was 10s.

6.10 Microieakage testing

A small cavity preparation was done at the apices of the teeth with a #330 carbide bur.

The cavity was then acid etched with 37% phosphoric acid for 20 seconds, washed for 20

seconds and dried with a gentle Stream of compressed air. Prime and Bond 2.1 adhesive

was applied and light cured for 20 seconds with Optilux 501 cunng larnp (SDS Ken).

Dyract restorative rnatenal (Dentsply, lot # 97 10000260) was used to restore the apical

preparation of the specimens. Two coats of nail vamish were applied to al1 surfaces 1

mm short of the coping margins. The specimens were submergeci in a 5% basic red

fuschin (Pararosanilin, Imperia1 Chemical industries) solution (Baldissara et al. 1998) for

24 h. Afier rinsing with water, each specimen was then embedded in clear acrylic

(Orthoresin) and sectioned twice bucco-lingually 1 mm fiom the mid-plane, through the

restoration with a diarnond saw blade (Amplex MD 150-N 100m-1/8) and Accutom

microsaw (Struers). Images of the specimen sections were captured with an intraoral

camera and color photographs of each section were printed. The degree of microleakage

at the dentin-cement interface was assessed with a microscope (30x magnification, TM-

20 1 toolmakers microscope, Mitutoyo, Tokyo, Japan) using a scale developed by Tjan et

al. (table 1 1, Tjan et al. 1992).

Table 11: Microleakage scale for the assessrnent of leakage at the dentin-cernent interface. (Adapted from Tjan et al. 1992)

I l 1 Leakage UD to 1/3 of the axial wall

Rating O

12 Y .

1 Leakaee UD to 2/3 of the axial wall 1

-

~ e s c r i ~ t i o n No leakarre

13 i Y .

1 Leakage alone the full leneth of the axial wall 1 I Y Y Y

4 1 Leakage extending over the occlusal surface

The presence or absence of microleakage was also noted at the cernent-coping interface.

6.1 1 Marginal adaptation

Marginal adaptation was assessed with a travelling microscope (30x magnification). The

toolmakers microscope (Mitutoyo, TM-201) is composed of an x-y stage, and high

precision digimatic micrometer heads (Mitutoyo, precision +/- 0.001 mm). Clear rope

wax was used to position the specimen on the microscope table. The long axis of the

tooth was placed in line with the y-axis. The microscope with its position sustained at the

x-mis, was moved along the y-axis for measurernent of the cernent thickness. The

dimension measured in this experiment is the marginal opening (Figure 9) when a line

connects the M and O reference points (May 1998). This measurement was chosen since

it is unaffected by overextension or underextension of the crowns. The marginal

adaptation was measured at 8 points along the crown margin (4 at labial and 4 at lingual)

fiom the sections of each specimen.

Fieure 9: Crown to tooth diagram showing measurement location of marginal opening (MO). (Illustration adapted from May, 1998)

7. Statistical analysis

7.1 Marginal adaptation

The SPSS software package was used to perform the statistical analysis. Descriptive

statistics were computed for margins, sections as well as crown and cernent type. Each

variable was investigated for significant differences in means using unpaired t-tests, one-

way ANOVA and Scheffe tests. The unit of measure was the margin. The combined

effect of al1 variables on the marginal adaptation was tested using a Cway ANOVA.

Multiple regression analysis was used to investigate how marginal adaptation was related

to the independent variables.

7.2 Microleakage

The microleakage data was cross-tabulated and subrnitted to chi-square analysis. Logistic

regression was used to predict the probability of microleakage occurring. Pearson's

correlation coefficient was used to assess the relationship between microleakage and

marginal adaptation. Intra-observer variability (kappa) was also computed.

8. Main Study

Following the analysis of the pilot study, it was determined that 80 specimens were

required for the main study. The teeth were divided in two main groups (Procera and

PFM copings) and 4 cernent sub-groups (Zinc phosphate, glass ionomer, resin-modified

glass ionomer and resin). The methodology followed was identical to the one previously

described in sections 6.1 to 7.2.

Results

9. Pilot studv

9.1 Marginal adaptation of PAC and PFM copings

There were no statistically significant differences in marginal adaptation between crown

types (fig. 1 O, p=0.587). Zinc phosphate cernent showed significantly (* fig. 10, p<0.00 1 )

larger cernent gaps ( 15 1 p) as compared to glass ionomer (101 p), resin-modified g las

ionorner ( 8 6 ~ ) and resin cement ( 10 1 p). There were no statistically significant

differences among glass ionomer, resin-modified glass ionomer and resin cement. No

significant difierences in marginal adaptation were found between margin locations (fig.

1 1, p=0.4 13), or section locations (fig. 12, p=0.82 1).

9.2 Microleakage of PAC and PFM copings

Procera copings exhibited less microleakage than PFM copings (*fig. 13, p-0.037). Zinc

phosphate cernent showed significantly more microleakage than the other cement types

(#fig. 13, p<0.00 1 ). Eighty seven percent of margins in the zinc phosphate cement group

exhibited extensive microleakage (score 4). There were no statistically significant

difierences among glass ionomer, resin-modified g las ionomer and resin cements. The

buccal margin displayed signi ficantly higher microleakage values than the lingual margin

(fig. 14, p=O.OOS). Fifty three percent of buccal margins exhibited microleakage

extending to the occlusal (score 4) and none of the buccal margins exhibited a

microleakage score of O. No significant difference in microleakage was found between

specimen sections (fig 15, p=0.944).

9.3 Correlation between microleakage and marginal adaptation

A modest but statistically significant association of 28.6% was found between

microleakage and marginal adaptation data (r=0.286, n= 128, p=0.00 1 ).

10. Main studv

10.1 Marginal ada~tation of PAC and PFM co~inas.

10.1.1 Crown type

There was a statistically significant difference in marginal adaptation between crown

types. frocera copings had a significantly larger mean marginal gap ( 5 4 ~ ) than PFM

(29p) copings (* fig. 16, p<O.OO 1 ).

1 0.1.2 Margin location

There were no statistically significant differences in marginal adaptation between buccal

and lingual margins (fig. 16) for Procera (p=0.2 18) or PFM (p=O.4 1 1) copings.

The variability due to crowns within groups was not significantly different from the

vanability due to sites within crowns. Therefore, the measurement points fiom different

sites within crowns could be treated as independent. However a failure in one of the

m e n s of the crown would mean a failure of the whole specimen and so the statistical

analysis was repeated using the crown (n=40) as the unit of measure to examine if similar

results would be achieved. Significant differences in marginal adaptation were found

according to crown type. Procera copings had a larger mean marginal gap than PFM

copings (*fig. 16A, p<0.001). These results are in agreement with those found using the

margin as the unit of measure (n=320) as described previously.

10.1 -3 Cernent type

Procera copings had significantly larger mean marginal gaps than PFM copings (*fig. 18,

p<0.001) in each cernent group. Zinc phosphate cernent showed significantly larger

mean marginal cernent gap values ( 5 4 ~ ) as compared to glass ionomer (40p), resin-

modified glass ionomer (37p) and resin cernent (37p) (#fig. 17, p<O.OOl)).

The statistical analysis was repeated using the crown as the unit of measure (n=40) and

significant differences in marginal adaptation were found according to cernent type.

Zinc phosphate cernent exhibited larger mean muginal cernent gaps than the other types

of cernent (*fig. 17A, pC0.05). These results are in agreement with those found using the

margin as the unit of measure (n=320) as described previously.

10.1 -4 Section location

The mean marginal adaptation of the copings was examined according to section

location. No statistically significant difference was found between mesial ( 4 0 ~ ) ~ mid-

mesial (43p), mid-distal(43p) and distal(41 p) sections (fig. 18, p-0.768).

10.1.5 Multiple regression model

Crown and cernent type remained significant once adjusted for al1 variables in the

multiple regression model (data not shown).

10.2 Microleakaee of PAC and PFM co~ines

10.2.1 Crown type

A significant association between crown types and microleakage scores was found. PFM

copings exhibited significantly less rnicroleakage than Procera copings (fig. 19, p<0.00 1 ).

Microleakage occurred at the cement and coping interface. This occurred in 3 1.5% of the

margins (1 0 1 /320) in the Procera group only (fig. 26).

10.2.2 Margin location

No significant association between margin location and microleakage was found.

Moreover, there were no statistically significant differences between buccal and lingual

margins of Procera and PFM copings (fig. 1 9, p=0.449).

The statistical analysis was repeated using the crown as the unit of measure (n=40) and

examining the mean number of margins exhibiting leakage extending along the full

length of the axial wall (score 3) or leakage extending to the occlusal surface (score 4)

according to crown type. Significant differences in microleakage were found between

Procera and PFM copings. Procera copings exhibited significantly more microleakage

than PFM copings (*fig. 19A, p<0.001). These results are in agreement with those

found using the margin as the unit of measure (n=320) as described previousl y.

10.2.3 Cernent type

When microleakage was examined according to cement type, a significant association

was found (fig. 20, p<0.001). The resin cernent was supenor showing the highest

percentage (65%) of "O-no leakage" scores, while the zinc phosphate cernent was

inferior, exhibiting the highest percentage (83%) of "4-leakage extending to the occlusal

surface" scores.

The statistical analysis was repeated once again using the crown as the unit of measure

(n4O) and significant differences in microleakage were also found according to cernent

type (fig. 20.4, p ~ 0 . 0 0 1 ). Zinc phosphate cernent perfonned significantly worse than the

three other types of cernent, exhibiting the highest number (7.9) of "3-leakage extending

along the full length of the axial wall" and "4-leakage extending to the occlusal surface"

scores (*fig. 20A).

10.2.3A-Zinc phosphate cernent

Figure 21 illustrates that 90 percent of PFM coping margins cemented with zinc

phosphate cement exhibited a score of "4'" i.e. leakage extending to the occlusal surface

(fig. 27). Seventy-six percent of Procera coping margins cemented with zinc phosphate

cernent exhibited similar extensive leakage (fig 28).

10.2.3B- Class ionomer cernent

Figure 22 shows that 66.3 and 48.8 percent of PFM (fig.29) and Procera (fig. 30) coping

margins respectively, did not exhibit any leakage (score O) when cemented with glass

ionomer cernent.

10.2.3C- Resin-modified glass ionomer cernent

In figure 23, 83.8 percent of PFM coping margins cemented with resin-modified glass

ionomer cernent showed no leakage (score 0) and none of the PFM margins exhibited a

score of 4. While as 35 percent of Procera coping margins exhibited leakage extending

along the full length of the axial wall (score 3) and 36.3 percent showed leakage to the

occlusal surface (score 4).

10.2.3D- Resin cernent

Figure 24 illustrates that 96.3 percent of PFM coping margins cemented with resin

cernent showed no leakage (score O) while 33.8 percent of Procera coping margins had

the same score. Forty-two percent of Procera coping margins had a leakage score of 3

and 20 percent had a leakage score of 4. None of the PFM coping margins showed

Ieakage extending to the occlusal surface (score 4).

10.2.4 Section location

The microleakage scores of the coping margins were exarnined according to section

location. No statistically significant association was found between section locations and

microleakage (fig. 25, p=0.482).

10.2.5 Logistic regression

Similar results were found when logistic regression was used to predict the absence or

presence of microleakage. According to this analysis, the nsk of microleakage was 1 1

times higher for Procera copings (OR= 1 1.0194, 95% C.I. = 7.0464 - 17.2323) in

cornparison with PFM copings when adjusted for cernent type as well as margin and

section location (data not shown).

10.3 Correlation between microleakaee and mareinal ada~tatioa

A modest but statistically significant association of 26.3% was found between

microleakage and marginal adaptation data ( ~ 0 . 2 6 3 , n=640, p<0.00 1 ).

10.4 Intra-observer variabilitv

The microleakage data was collected twice by the same examiner and an 86.7%

agreement (K=0.867) was found.

Figure IO-Pilot: Mean marginal adaptation of PAC and PFM copings. There were no statistically significant differences in marginal adaptation between crown types ( ~ 0 . 5 8 7 ) . Zinc phosphate cernent showed significantly larger

cernent gaps (*p<0.001) as compared to al1 other cements. Each bar represents the mean of 16 margins (n=16) and the vertical bar shows the standard deviation of the mean.

Zinc phosphate G I RMGl Resin

Cernent type

Figure Il-Pilot: Mean marginal adaptation of PAC and PFM copings according to margin location. No statistically significant difference in marginal adaptation was found between buccal and lingual margins. (p=0.413). Each bar represents the mean of 32 margins (n=32) and the vertical bar shows the standard deviation of the mean.

Buccal Lingual

Margin Location Procera

Figure 12-Pilot: Mean marginal adaptation of PAC and PFM copings according to section location. No statistically significant difference in marginal adaptation was found between the four section locations (p=0.82 1 , ANOVA). Each bar represents the mean of 32 margins (n=32) and the vertical bar shows the standard deviation of the mean.

Mesial Mid-mesial Mid-distal Oistal

Section Location

Figure 13-Pilot: Percentage of PAC and PFM coping margins showing extensive microleakage extending to the occlusal (score 4) according to cernent type. There is a signi ficant di fference in microleakage between crown types (*p=0.037). PAC copings showed less microleakage than PFM copings and zinc phosphate cernent performed significantly inferior to the other cernent types (#p<0.00 1 ).

Zinc phosphate GI RMGl Resin

Cernent types

Figure 14-Pilot: Percentage of PAC and PFM coping margins showing V ~ ~ O U S microleakage scores according to margin location. The 90-degree buccal shoulder margin exhibited significantly worst miroleakage values than the lingual chamfer margin (x2=9.683, 2 d.f., p=0.008). Microleakage score 1-3 were grouped due to low ce11 counts in the chi-square test. Each bar represents a percentage of 8 margins.

Lingual

Microleakage Scores

Figure 15-Pilot: Number of PAC and PFM coping margins showing various microleakage scores according to sections. There is no significant association between section location and microleakage (x2=1.714, 6 d.f., p=0.944). Each bar represents a number out of 32 margins. Microleakage scores 1-3 were grouped due to low ceIl counts in the chi square test.

Mesial 1 Microleakage Scores

Mid-mesial Middistal Distal

Figure 16: Mean Marginal Adaptation of PAC and PFM Copings. PAC copings had a significantly larger mean marginal gap than PFM copings (* p<0.00 1 ). No statistically signi ficant di fference in marginal adaptation was found between buccal and lingual margins for PAC (p=0.218) or PFM copings (p=0.4 1 1). Each bar represents the mean of 160 margins (n= 160) and the vertical bar shows the standard deviation o f the mean.

Buccal Lingual

Procera

Crown Type

PFM

Figure - 16A: Mean Marginal Adaptation of PAC and PFM Copings. PAC copings had a significantly larger mean marginal gap than PFM copings (*p<0.001). Each bar represents the mean of margins for 40 crowns (n=40) and the vertical bar shows the standard deviation of the mean.

Proce ra PFM

Crown Type

Figure - 17: Mean marginal adaptation of PAC and PFM copings according to cement type. PAC copings had a significantly larger mean marginal gap than PFM copings (*p<O.00 1). Zinc phosphate cernent showed significantly larger mean marginal gap values as compared to the other cements. (#p<0.001, ANOVA, Scheffe). Each bar represents the mean of 80 margins (n=80) and the vertical bar shows the standard deviation of the mean.

Zinc phosphate GI RMGl Resin

Cernent Type - *PAC PFM

Figure 17A: Mean marginal adaptation of PAC and PFM copings according to cernent type. Zinc phosphate cernent showed significantly larger mean marginal gap values as compared to the other cements (*p<0.05, ANOVA, Duncan). Each bar represents the mean of margins for 20 crowns (n=20) and the vertical bar shows the standard deviation of the mean.

Zinc phosphate

Cerne

RMGI

Type

Resin

Figure 18: Mean marginal adaptation of PAC and PFM copings according to section location. No statistically significant difference in marginal adaptation was found between the four section locations (p=0.768, ANOVA). Each bar represents the mean of 160 margins (n=160) and the vertical bar shows the standard deviation of the mean.

Mesial Mid-mesial Mid-distal Distal

Section Location

Figure 19: Percentage of PAC and PFM coping margins showing various microleakage scores according to margin location. There is a significant association between crown type and microleakage scores (x2=1 04.64 1,4d.E, p<0.001). PFM copings show less microleakage than PAC copings. There is no significant association between margin location and microleakage (x2=3.695, 4d.f., p=0.449). Each bar represents a percentage of the 160 margins obsewed per group (n=160).

60 -

50 -

40 -

30 -

20 -

I O -

O -,

l B Buccal PAC

Buccal PFM

Lingual PAC

Lingual PFM

Microleakage Scores

Figure - 19A: Mean number of PAC and PFM margins exhibiting leakage extending along the full length of the axial wall (score 3) or leakage extending to the occlusal surface (score 4). PAC copings showed significantly more microleakage than PFM copings (*p<0.001). Each bar represents the mean number of margins showing a score of 3 or 4 (n=320) and the vertical bar is the standard deviation of the mean.

Procera ?FM

Crown Type

Figure 20: Percentage of PAC and PFM coping margins showing various microleakage scores according to cernent type. There is a significant association between cernent type and microleakage scores (x2=327.812, 12 d.f., p<O.OOl). The resin cernent showed the highest percentage of "O-no leakage" scores, while the zinc phosphate cernent had the highest percentage of "4-leakage up to the occlusal surface" scores. Each bar represents a percentage of 160 margins.

O 1 2 3 4

Microleakage Scores

Zinc Phosphate Glass lonomer Resin Modified Glass lonomer Resin

Figure 20A: Mean number of PAC and PFM coping margins exhibiting leakage extending along the full length of the axial wall (score 3) or leakage extending to the occlusal surface (score 4) according to cernent type. Zinc phosphate cernent exhibited significantly more leakage than the three other

cements (*p<0.001, ANOVA, Scheffe). Each bar represents the mean number of margins showing a score of 3 or 4 (n=160) and the vertical bar is the standard deviation of the mean.

Zinc phosphate G I RMGl Resin

Cernent Type

Figure 2 1 : Percentage of PAC and PFM coping margins cemented with zinc phosphate cernent showing various microleakage scores. Each bar represents a percentage of 80 margins (n=80).

* Microleakage Scores

Figure 22: Percentage of PAC and PFM coping margins cemented with glass ionomer cernent showing various microleakage scores. Each bar represents a percentage of 80 margins.

O 1 2 3 4

Microleakage Scores

Procera (?=124.01, 12 d.f.. pc0.001) PFM (x2=290.62, 12 d.f., p<0.001)

Figure 23: Percentage of PAC and PFM coping margins cernented with resin-modified-glass ionomer cernent showing various microleakage scores. Each bar represents a percentage of 80 margins.

Microleakage Scores

Procera (x2= 124.01, 12 d.f., p~0.001) PFM (x2=290.62, 12 d.f., p<0.001)

Figure 24: Percentage of PAC and PFM coping margins cemented with resin cernent showing various microleakage scores. Each bar represents a percentage of 80 margins.

O 1 2 3 4 Microleakage Scores

Procera (x2=1 24.01, 12 d.f., pc0.001) PFM (x2=290.62, 12 d-f., p<O.OOl)

Figure 25: Percentage of PAC and PFM coping margins showing various microleakage scores according to section location. There is no significant association between section location and rnicroleakage (x2=1 1.55,12 d.f., p=0.482). Each bar represents a percentage of 160 margins obsewed.

O 1 2 3 4

Microleakage Scores

Mesial Mid-mesial Middistal Distal

Fieure 26: Procera coping specimen showing microleakage at the cernent-coping interface

Fieure27: Microleakage specimen of a PFM coping cemented with zinc phosphate cernent.

Fieure 28: Microleakage specimen of a Procera coping cemented with zinc phosphate cernent

Figure 29: Microbakage specimen of a PFM coping cemented with glass-ionomer cernent.

Figure 30: Microleakage specimen of a Procera eoping cemented with glass ionomer cernent

Fieure 31: Microleakage specimen of a PFM coping cemented with resin-modified-glass ionomer cernent.

Fieure 32: Microleakage specimen of a Procera coping cemented with resin-modificd-glass ionomer cernent.

Fieure 33: Micoleabge specimen of a PFM coping cemented with resin cernent

Fieure 31: Microleakage specimen of a Procera coping cemented with resin cement.

Discussion

The study was designed to elucidate the marginal adaptation of Procera AllCeram crowns

in cornparison with PFM crowns and to investigate their microleakage when cemented

with zinc phosphate, glass ionomer, resin-rnodified-glass ionomer or resin cernent.

No statistically significant difference in marginal adaptation data was found between

crown types while Procera copings exhibited less microleakage than PFM copings in the

pilot study. These results are in sharp conhast with the results of the main study. This

difference can be explained by several factors. Namely, a less experienced technician

fabncated the PFM copings in the pilot siudy while an experienced technician was hired

for the main study. Moreover, the Procera scannings were al1 done by a novice

technician and although proper training was acquired, a leaming curve is to be

antiçipated.

In the main study, it was demonstrated that Procera copings had a significantly larger

mean marginal gap and exhibited more microleakage than PFM copings. Zinc phosphate

cement showed significantly larger mean marginal gap values and was inferior in

microleakage testing as compared to the other cements. Resin cernent showed the lowest

degree of microleakage.

Natural teeth show a large variation because of their age, individual structure, storing

medium and time afier extraction, thus causing dificulties in getting standardized

abutrnents. Several authors have employed steel dies for rneasurernents of the marginal

accuracy (Holmes et ai. 1992, Rinke et al. 1995). The advantage of this method is the

possibility of a standardized preparation for al1 abutments. However, these abutments do

not give information relatice to the microstructure of the hard tissue of the teeth

(Beschnidt and Strub 1999) and would not have permitted the microleakage testing

component of this expenment.

11. Mareinal adaptation

It is important to know how well a crown tits the tooth at the margin. A defective margin

may invite caries and penodontal disease and was found to be the third most fiequent

cause of failure of crowns and fixed partial dentures (Schwartz et al. 1970). It is

estimated that 30-40 pm is clinically detectable as a marginal deficiency (Chnstensen

1966). Conversely, McLean and vonFraunhofer observed that an explorer after 3 week's

of clinical use is incapable of disceming margins of less than 80 pm opening (McLean

and vonFraunhofer 1 97 1 ).

The results of this study are difficult to compare with the results of previous in vivo and

laboratory studies (table 3) due to the differences in methodology used in marginal

discrepancy evaluations.

11.1 Effect of crown type

There are few studies that have exarnined the marginal adaptation of Procera crowns

(table 12). Al1 reported marginal fit values range fiom 56 to 145 microns (Boening 1992;

Sulaiman et al. 1997, May et al. 1998, Razzoog et al. 1997). Our finding of mean

marginal gap for Procera crowns (54pm) and PFM crowns (29pm) is significantly

smaller. This significant difference could be explained by the shape-related error of the

Procera scanner. Errors of up to 10 microns have been reported. The dimensions of the

bal1 at the probe tip limits the ability to resolve small cavities and grooves on the surface

of the preparation. Therefore the milling procedure is not able to create small

irregularities. The clinical consequence of this filtering is an enlargement of the cernent

space locally. Extruding parts are more critical, both for correct seating of the crown and

for marginal adaptation at the finish line. If extruding parts are neglected in the reading,

it is possible that the crown will stick at these parts and will not adapt at the finish line

(Persson M. et al. 1995). Moreover, the Procera copings are manufactureci by compacting

alumina powder against enlarged models of the tooth preparation. The tooth preparation

models are made with an enlarging copy milling machine and this enlargement is

calculated fiom the sintering of the compacted powder. This estimation is to compensate

for the shrinking which accompanies the sintering process. Some discrepancies in

marginal fit may be attnbutable to the manufacturing process.

Although significant, the difference in marginal adaptation between the two types of

crowns begs the question; is this difference clinically significant? AAer examining more

than 1000 crowns clinically afier a 5-year penod, McLean and vonFraunhofer concluded

that a marginal opening of less than 120 microns was clinically acceptable (McLean and

vonFraunhofer, 197 1 ). Consequently the difference in marginal adaptation found in this

study between the Procera and PFM crowns, would not be considered clinically

significant.

Table 12: Procera AUCeram crown mean marginal adaptation values according to differen t studies.

11.2 Effect of finish line

Sulaiman et al. 1997 May et al. 1998

Boening et al. 2000

Previous studies have shown contradictory evidence as to which finish line provides the

Method of Detection Reference

best marginal adaptation of the final restoration. Gavelis et al. studied the seating

Mean Marginal Adaptation (pm)

83

capacity of full cast crowns cemented ont0 standardized metal dies prepared with seven

In vitro fit on master die.

different marginal designs. The order of seating fiom best to worst was: feather-edge,

chamfer and shoulder with 85-degree (parallel) bevel, 90-degree shoulder, 45-degree

56 Premolars 63 Molars

80-95 Anterior 90- 145 Posterior

shoulder, shoulder wi th 30-degree and 45-degree bevels. The results indicated that the

Ivorine teeth replica technique. In vivo silicone replica technique.

90-degree shoulder was almost as well seated as the feather-edge and parallel bevel

margins. This unexpected finding was attributed to the rapid cernent escape at the

shoulder margin (Gavelis et al. 198 1). Conversely, Kay et al. used a computer modei to

examine the factors affecting the seating and fit of complete crowns, and found no

significant difference in fit between the seven finish lines tested (Kay et al. 1986).

Moreover, Our findings did not show any statistically significant difference in marginal

adaptation between the shoulder and charnfer preparations. This is in agreement with

current evidence which suggests that there is no significant difference in fit between

various finish lines. Therefore, this factor did not seem to be a signifiant confounder in

Procera and PFM marginal adaptation data analysis.

1 1.3 Effect of the marginal design of the coping

It would seem that margin design had no effect on the fit of PFM copings. No difference

was found between the disappearing metal margin on the buccal and the 1 mm metal

collar on the lingual. These results are in accord with a finite element analysis study.

DeHoff and Amusavice found that the design of the margin did not affect the ultimate fit

of the restoration (DeHoff and Anusavice, 1984). On the other hand, some studies

support the theory that the placing of additional metal at the gingival margin reinforces

this margin and thus inhibits marginal distortion due to porcelain firings (Faucher and

Nicholls 1980). The effect of margin design on marginal adaptation following veneering

porcelain application was beyond the scope of this study.

1 1.4 Effect of porcelain veneering

Previous studies have shown that the fit of a ceramo-metal casting deteriorates during the

finng of a porcelain veneer. The contnbuting factors remain uncertain however, the

literature has suggested certain causes that may be responsible for the distortion such as:

porcelain contraction, contamination of the casting that reduces the melting temperature,

progressive reduction in the resilience of the metal caused by hardening of the porcelain,

design of the metal substructure and inadequate support of the metal fiamework dunng

firing (VanRensburg and Strating 1984). Silver et al. observed that if the marginal metal

was thinned beyond 0.5 mm, the porcelain when applied would bend in the thin portions

causing a change in fit (Silver et al. 1960). Conversely, Hamaguchi et al. exarnined four

margin designs (shoulder, bevelled shoulder, chamfer and bevelled chamfer) using a

scanning electron microscope technique. They could not find significant distortion of the

facial margin on any of the four margin designs after porcelain application (Hamaguchi

1982). In Our experiment, the effect of veneenng porcelain application was simulated

through cycling in a porcelain tùniace. What is more, there are no in vivo studies to our

knowledge reporting on the misfits of PFM crowns following the application of

porcelain. Therefore, it is presumed that this effect is not clinically significant.

1 1.5 Effect of cernent

Well-adapted margins prohibit the escape of cernent thereby increasing hydraulic

pressure and adversely affecting the final seating. Consequently, a close marginal

adaptation of a complete crown to a die prier to cementation may contribute to marginal

openings of cemented crowns (Moore et al. 1985). This experiment could have been

improved by measuring the pre-cementation marginal adaptation of the copings. A

correlation could then have been established between the pre- and pst-cementation

marginal adaptation. However, this testing is done via a silicone replica technique that

may no t accuratel y represen t marginal discrepancies (Rosenstiel and Gegauff 1 988,

Fransson et al. 1985).

Many studies on marginal adaptation have already demonstrateci that cast crowns do not

seat completely when cemented (Gavelis 1 98 1 ). The incomplete seating of the crown is

caused by the thickness of the cernent film that accumulates at the occlusal surface of the

prepared tooth (Cagidiaco 1992). Zinc phosphate had a significantly larger mean

marginal gap than the other three types of cernent. Our findings are similar to a study by

Wang et al. These authors have shown that the seating discrepancy of cast crowns was

significantly greder with zinc phosphate than with glass ionomer cernent. This

observation was attributed to the difference in flow of each cernent, narnely, the viscosity

of zinc phosphate cernent increased rapidly upon mixing (Kay 1986) while that of g l a s

ionomer cernent remained fairly constant before setting (Wang et al. 1992).

Another interesting finding is that an unusual filtration process occurs in zinc phosphate

cements durhg cementation. Excess cernent is forced out through the narrow passage

between the surface of the crown and the prepared tooth. Eventually, the passage is so

reduced in size that larger grains become lodged at the entrante. Cement liquid filtration

occurs, resulting in an uneven distribution of cement powder particles in the phosphate

matrix. This process might account for some variation in film thickness (Jorgensen

1960).

Resin materials have been shown to increase in viscosity rapidly and prevent the outward

flow of cement from the margins of copings. This is caused by the immediate

exponential setting mechanism of resin cements (White 1993). Our results are in contrast

with several other studies which have shown that copings cemented with resins have the

poorest seating (Tuntiprawon 1999, Stanicec et al. 1988). C & B Metabond resin cement

exhibited the smallest mean marginal gap value (37 p). A possible explanation for this

result is that the mixing of this cernent is very cntical. Meyers et al. demonstrated that

alterations in the powder/liquid ratio can significantly affect the film thickness of this

material. Increased powder resulted in a more viscous mixture and increased film

thickness (Meyers et al. 1993). Properly cooled and mixed C & B Metabond, used

immediately after mixing can produce a film thickness of about 20 microns. However, if

the cement as well as the prosthesis are not cooled, or the mixing process is too slow, it

c m reach a film thickness of over 100 microns within 60 seconds (van der Vyer 1998).

In this study the matenal was pre-cooled but the prosthesis was not, which might explain

the slightly higher mean marginal adaptation value than the above-mentioned (20 p). In

summary, when the proper precautions are taken the working time of resin cements can

be increased, which allows for proper seating of the restoration.

12, Microleakaee

12.1 Effect of cernent

It is difficult to eliminate the cement line at the margin of full coverage restorations. For

this reason, we still rely on the properties of the cernent to maintain the marginal seal.

Under normal oral environmentat conditions, different luting cements show different

degrees of microleakage. The physical properties which influence the marginal seal

obtained by a material include the degree to which it bonds to tooth structure, its

shrinkage at the time of setting, water absorption, solubility and coefficient of thermal

expansion. Clinical factors which c m lead to the breakdown of the marginal seal include

occlusal stresses, intra-oral pH and thermal fluctuations as well as abrasion.

12.1.1 Bond to tooth structure

The more firmly a restoration adheres to the tooth, the better the marginal seal. Zinc

phosphate cernent lacks micro-mechanical and chemical bonds to dentin which would

explain why it exhibited extensive microleakage in this study. On the other hand, glass

ionomer, resin-modified glass ionomer and resin cements bond chemically to tooth

structure. The bond strength between composite resin and dentin is the highest among al1

cements (table 4). The minimal amount of microleakage displayed by the resin cernent

group in this study, can also be explained by the obstruction of the dentinal tubules by

resin tags (Lyons et al. 1997).

12.1.2 Water absorption and solubility

The specimens were stored in water at body temperature for 24 hours before

thermocycling. This is a brief period compared with the life expectancy of a cast

restoration, but luting agents are more susceptible to dissolution during and immediately

after their initial set (Swartz 197 1 ). The water-soluble materials (zinc phosphate, glass

ionomer and resin-modified-glass ionomer) could have deteriorated dunng early storage.

The insoluble resin cement could have absorbed water dunng storage that may have

allowed relaxation of intemal stresses caused by pol yrnenzation shrinkage (Davidson et

al. 1984). This may have decreased their potential for interfacial failure dunng

thermocycling (White 1995).

12.1 .S Dimensional changes

The dimensional changes occumng in dental cement can be divided into three categones:

(i) contraction during setting; (ii) expansion and contraction due to contact with moisture;

and (iii) expansion and contraction due to changes in temperature.

These changes in dimension are not much of a problern with luting cernent since it is a

thin film. The coefficient of thermal expansion for most of the cernents used closely

resembles the 1 1 x 1 om6 PC of dentin, so the expansion and contraction probably has little

effect as a factor directly causing marginal breakdown (Mitra 1994). Resins tend to

absorb water during setting and a subsequent hygroscopic expansion occurs. This

expansion could compensate for their original setting contraction and contnbute to less

dye penetration (Crim 1987).

Myers et al. have reported higher marginal microleakage when vamish was not applied

during initial setting of glass ionomer cements (Myers et al. 1983). Al1 the margins in

this study were placed lmrn below the cemento-enarnel junction. Varnish was not applied

since it was shown that when the margin is below the gingival border, the application of

varnish is not effective. Dissolution occurs by exudate from the periodontal pocket,

leading to the detenoration of the marginal seal.

The results of this study are in agreement with several other papers that have reported

that zinc phosphate cement allows considerable percolation of dye from marginal dentin

(White 1995, White et al. 1994, Goldman 1992, White 1992, Shiftlett 1997). While

specimens cemented with resin cements exhibit substantially less marginal leakage (Tjan

1992, Staninec 1 988). Minimal solubility, superior strength and improved retention are

other advantages of resin materials (Tjan 1990, Tuntiprawon 1999).

12.2 Effect of therrnocycling

The specimens in this study were artificially aged by thermal cycling. The thermal cycles

could produce significant strains and microshifis on the restorations interface causing the

failure of the weakest link i.e. cernent interface despite the relatively low number of

thermal cycles adopted in this study (Baldissara et al. 1998). It has been suggested that as

thetmal stresses act rapidly to produce microleakage, prolonged cycling is unnecessary.

Cnm et al. found no difference in dye penetration when the specimens were cycled

between 100 and 1500 times and between 250 and 1 O00 times (Crim et al. 1987). in the

PFM group, thermal cycling applies mechanical forces to the luting agents between high

expansion castings (coefficient of thermal expansion 14.7 x 1 o4 p/OC) and low-expansion

dentin (1 1 x 1 0 - ~ p/OC) (Bullard et al. 1988). It is possible that the mean marginal

adaptation and microleakage results for the PFM group would have been even better had

the specimens not been therrnocycled.

Some expenments incorporate mechanical fatiguing of the specimens in their protocol

before submitting them to fùrther testing. However, Beschnidt and Strub evaluated the

marginal accuracy of all-ceramic crown systems using the PFM as a control before and

afier cyclic preloading in an artificial mouth. They concludeâ that simulated ageing in

the chewing simulator had no significant influence on the marginal fit of al! specimens

(Beschnidt and Strub 1999).

12.3 Microleakage at the coping and cernent interface

Microleakage can also occur at the coping-cernent interface which may result in

loosening of the cast restoration (Jacobs et al. 199 1 ) and subsequent recument decay due

to the infiltration of micro-organisms in the cement space. This was observed in 3 1.5%

( 1 0 1 /32O) of the Procera margins. No microleakage occurred at this interface in the PFM

group. Procera manufacturers do not specie the required preluting treatment of the

fitting surface of the crown. Results of this study would indicate that a surface treatment

of the Procera coping might be beneficial to improve its bond with the cernent. To date,

no studies have looked at the effect of various surface treatments on microleakage. Blixt

et al. examined the influence of surface treatment i.e. untreated, sandblasting and

silanating on the bond strength of various cements to the Procera coping. The

sandblasted surfaces were very similar to the untreated subgroup. The silanated subgroup

demonstrated the highest shear force values for al1 matenals (Blixt et al. 2000). Awliya

et al. also examined the influence of surface treatments Le. air abrasion with 25 or 50

microns aluminum oxide at V ~ ~ O U S pressures on bond strength of resin cement to Procera

copings. The highest bond strength was obtained with air abrasion with 50 micron

alumina particles at 80 psi (Awliya et al. 1998). Future studies should investigate the

effect of sandblasting and silanating on microleakage of Procera crowns.

12.4 I n vivo vs. in vitro microleakage testing

The importance of microleakage in clinical dentistry is well recognized but the exact

point at which microleakage becomes clinically signifiant is at present unidentifieci

(Lyons et al. 1997). Few in vivo microleakage investigations of luting agents in humans

are reported. White et al. examined the in vivo microleakage of luting cernents for cast

crowns. The metal ceramic crowns were randomly cemented with zinc phosphate, resin-

modified g las ionomer or resin-modified glass ionomer with a dentinal bonding agent to

penodontally compromised molars. After 6 months, the teeth were extracted, stained,

embedded, sectioned and the microleakage measured (White et al. 1994). The results of

the study were in agreement with prior in vitro studies, both with respect to relative

amounts and to location of leakage. This suggests that in vitro mode1 systems using

themocycling may accurately predict clinical performance.

In vitro studies of microleakage should be regarded as setting a theoretical maximum

amount of leakage that may occur in vivo. There is generally a poor correlation between

the extent of microleakage found irz vitro and the clinical success of a matenal. Zinc

phosphate has been used for over 90 years and its historic success does not correlate with

its poor performance in il1 vitro testing. In the present context of chemical adhesion

bonding, it has been suggested that zinc phosphate cernent's limited success may be due

to presently unknown properties such as antimicrobial aïtivity (White 1992).

In vivo, oral tluids and pulpal pressure lead to a moist surface which c m deteriorate the

marginal adaptation of the iuting cernent. Lyons et al. used an intra-pulpal pressure

charnber to simulate this moist surface in extracted teeth in vitro (Lyons 1997). Similar

results were found i.e. microleakage occurred in crowns cemented with zinc phosphate

and glass ionomer cmen t s while no microleakage was detected with the resin cemented

crowns. The lack of tubular outflow in the extracted teeth used would also explain the

large magnitude of microleakage observeci. It has been previously suggested that an

outward dentinal fluid flow from the pulp may mechanically hinder bacterial growth into

tubules (Olgart et al. 1974).

To date, there is no universally accepted technique used to determine the microleakage

patterns of restorative matenals. Some authors argue that microleakage tests conducted

with dyes are not clinically relevant. They advocate the use of clinically relevant

material such as lipopolysachandes or ce11 wall materials that have been shown to

provoke inflammatory reactions in the dental pulp. Several studies have suggested that

various leakage detection methods do not yield equivalent results, therefore they should

not be compared (Crim et al. 1985, Charlton et al. 1992). Conversely, it was found that

the use of either a dye o r an isotope was equally effective in demonstrating microleakage

and each penetrated the toothhestoration interface to a similar degree (Crim et al. 1987).

In vitro microleakage tests carried out with dyes are considered stricter than those camed

out in the oral cavity (Jacobs 199 1). This is most likely due to many reasons such as: the

dye is more easil y diffised than bacteria and their by-products, the build-up of proteins in

the marginal opening may improve the seal and the dentinal fluid in viable teeth may

contrast molecular penetration (Baldissara 1998). On this basis, if a material responds

positively to the dye tests, it is likely to respond even better on a clinical level (Baldissara

1998, Pashley 1990).

13. Correlation between marginal adaptation and microleakaee

A very modest but statistically significant correlation of 26.3% was found between

microleakage and marginal adaptation data. These results are consistent with Fick's law

of diffusion (Jacobs et al. 199 1). Similarly, White et al. found no significant correlation

between variables of marginal opening and microleakage of cemented cast crowns

(White et al. 1994).

Although caries/periodontal disease is commonly associated with inadequate margins,

pathology-fkee deficient margins have also been observed (Schwartz et al. 1970).

Therefore, other factors such as the nature of the rnicrobiologic flora, immunology, diet

and oral hygiene practices may have a major role in the etiology of disease associated

with restorations (White et al. 1994).

14. Future research

An important determinant of the clinical success of ceramic restorations is the bond

strength of the luting agent to the fitting surface and the prepared tooth structures. in this

study, Procera AllCeram copings exhibited microleakage at the coping-cernent interface.

Further in vitro investigation would be required to determine the best preluting treatrnent

of the fitting surface of the aluminous oxide coping.

In vitro laboratory assessment provides useful information to aid manufacturers and

researchers in choosing materials for prosthetic restorations before their introduction to

the dinical setting. In this experiment, attempts were made to simulate standard clinical

procedures but these are not a substitute for the complex oral environment. In vitro

testing is limited in its ability to predict survival in vivo. However, the results of this

study substantiate the need for a well-controlIed clinical trial study.

Conclusion

Within the limits of the findings of this investigation it may be concluded that:

1. The marginal adaptation of PFM copings was found to be significantly superior to

that of PAC copings. The use of zinc phosphate cernent resulted in significantly

larger marginal gap values than with g l a s ionomer, resin-modified-glas ionomer

or resin cements.

2. The microleakage of PFM copings was found to be significantly better than that

of PAC copings. Specimens cemented with zinc phosphate cernent showed the

most microleakage, followed by the ones cemented with glass ionomer and resin-

modified-glass ionomer cernent. Resin cernent was superior in microleakage

testing.

3. No significant difference in marginal adaptation and microleakage was found

between the labial and lingual margins of PAC or PFM copings.

4. There was a modest (26.3%) but statistically significant correlation between the

marginal adaptation and the microleakage data of the specimens.

References

1 . Abbate MF, Tjan AHL, Fox WM. Cornparkm of the marginal fit of various

ceramic crown systems. J Prosthet Dent 1989; 6 1 : 527-3 1.

2. Adair PA, Grossman DG. Esthetic Properties of Lost Tooth Structure Compared

with Ceramic Restorations. J Dent Res 1982; 62 : 292.

3. Alkurnru HN, Wilson HJ, Bor S. The Fit of all-ceramic crowns cernented with

different luting agents. J of Marmara University 1 992; l(3); 198-202.

4. Ames WB, A new oxyphosphate for crown seating. Dent Cosmos 1892; 34: 392-3

5. Andersson M, Odén A. A new al1 ceramic crown. A dense sintered, hi&-purity

alumina coping with porcelain. Acta Odontol Scand 1993; 5 1 59-64.

6. Andersson M, Razzoog ME, Odén A, Hegenbarth EA, Lang BR. Procera: A new

way to achieve an all-ceramic crown. Quintessence Int 1998; 29: 285-96.

7. Anusavice KJ. Degradability of dental ceramics. Adv Dent Res. 1992 Sep;6: 82-9.

8. Assif D, Rimer Y, Aviv 1. The flow of zinc phosphate cernent under a full-

coverage restoration and its effect on marginal adaptation according to the location of

cernent application. Quintessence Int 1987; 18 (1 1 ): 765-774.

9. Attanasi RC, Yaman P, Lang BR et al. Evaluation of color stability of Procera

AllCeram Porcelain. J Dent Res 1997; 75: 284.

10. Attard NJ, Dong CC. An Introduction to Cwrent Views on Dental Ceramics in

Prosthodontics. Ontario Dentist 2000; 77 (5): 2 1-25.

I I . Awliya W, Oden A, Yaman P et al. Shear bond strength of a resin cernent to

densely sintered high-purity alumina with various surface conditions. Acta Odontol

Scand 1 998; 56 ( 1 ): 9- 1 3.

12. Baldissara P, Comin G, Martone F, Scotti R. Comparative study of the marginal

microleakage of six cements in fixed provisional crowns. J Prosthet Dent 1998; 80(4):

4 1 7-422.

13. Belser UC, MacEntee MI, Richter WA. Fit of h e e porcelain-fused-to-metal

marginal designs in vivo: A scanning electron microscope study. J Prosthet Dent 1985;

53: 24-29.

14. Beschnidt SM, Strub JR. Evaluation of the marginal accuracy of different all-

ceramic crown systems after simulation in the artificial mouth. J Oral Rehab 1999; 26:

582-593.

15. Blixt M, Adamczak E, Linden LA et al. Bonding to densely sintered alumina

surfaces: effect of sandbiasting and silica coating no shear bond strength of luting

cernents. Int J Prosthodont 2000; 13 (3): 22 1-226.

16. Boening KW, Walter MH, Reppel PD. Non-cast titanium restorations in fixed

prosthodontics. J Oral Rehabil 1992; 19: 28 1-287.

17. Boening KW, Wolf BH, Schmidt AE et al. Clinical fit of Procera AllCeram

crowns. J Prosthet Dent. 2000 Oct;84(4):4 19-24

18. Bullard RH, Leinfelder KF, Russel CM. Effect of the coefficient of thermal

expansion on microleakage. J Am Dent Assoc 1988; 1 16: 87 1-877.

19. Cagidiaco MC, Ferrari M, Bertelli E et al. Cernent thickness and mimleakage

under metal-ceramic restorations with a facial butted margin: An in vivo investigation.

Int J Perio and Restorative Dent 1992; 12 (4): 325-332.

20. Campagni WV, Prince J, Defieese C. Measurement of coating agents used for

surface protection of Stone dies. J Prosthet Dent 1986; 55 (4): 470-474.

2 1. Chan C, Weber H. Plaque retention on teeth restored with full-ceramic crowns: a

comparative shidy. J Prosthet Dent. 1986 Dec;56(6):666-7 1.

22. Charlton DG, Moore BK. In vitro evaluation of two microleakage detection tests.

J Dent 1992; 20: 55-58.

23. Cho GC, Donovan TE, Chee WWL. Rational Use of Contemporary All-Ceramic

Crown Systems. CDA Journal l998,26(2): 1 13- 120.

24. Christensen GJ. Glass ionomer as a luting material. J Am Dent Assoc 1990; 120:

59-62.

25. Christensen GJ. Marginal fit of gold inlay castings. J Prosthet Dent. 1966 Mar-

Apr; 16(2):297-305

26. Cooper TM, Christensen GC, Laswell HR, Baxter R. Effect of venting on cast

gold full crowns. J Prosthet Dent 197 1 ; 26: 62 1-625.

27. Craig, R. G., ed. Restorative Dental Materials. 9th ed., St. Louis:C. V. Mosby,

1993.

28. Crim GA, Swartz ML, Phillips RW. Comparison of four thermocycling

techniques. J Prosthet Dent 1985; 53: 50-53.

29. Cnm GA, Garcia-Godoy F. Microleakage: The effect of storage and cycling

duration. J Prosthet Dent 1987; 57 (5): 574-576.

30. Davidson CL, De Gee AJ, Feilzer A. The competition between the composite-

dentin bond strength and polymenzation contraction stress. J Dent Res 1984; 63: 1396-

1399.

3 1. DeHoff PH, Anusavice KJ. Effect of metal design on marginal distortion of

metal-cerarnic crowns. J Dent Res 1984; 63: 1327-1331.

32. De Wald JP. The use of extracted teeth for in vitro bonding studies: A review of

infection control considerations. Dent Mater 1997; 13: 74-8 1.

33. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for

fixed prosthodontics. J Prosthet Dent 1999; 8 1 : 135- 14 1.

34. Faucher, R.R., Nicholls J. Distortion related to margin design in porcelain-fused-

to-metal restorations. J Prosthet Dent 1980; 43 : 149.

35. Ferrari M. Cernent thickness and microleakage under Dicor crowns: an in vivo

investigation. Int J Prosthodont. 199 1 Mar-Apr;4(2): 126-3 1.

36. Fransson B, Oilo G, Gjeitanger R. The fit of metal-cerarnic crowns, a clinical

study. Dent Mater 1985; 1 : 197- 199.

37. Gavelis JR, Morency JD, Riley ED, Sozio RB. The effect of various finish line

preparations on the marginal seal and occlusal seat of full crown preparations. J Prosthet

Dent. 1981,45 (2): 138-145.

38. Goldman M, Laosonthom P, White RD. Microleakage-full crowns and the dental

pulp. J Endod 1992; 1 8: 473-475.

39. Goodis HE, Marshall GW Jr, White JM, Gee L, Hornberger B, Marshall SJ.

Storage effects on deiitin permeability and shear bond strengths. Dent Mater 1993; 9(2):

79-84.

40. Grajower R, Zuberi Y, Lewinstein 1. Improving the fit of crowns with die

spacers. J Prosthet Dent 1989; 61: 555-563.

41. Grey NJ, Piddock V, Wilson MA. In vitro cornparison of conventional crowns

and a new all-ceramic system. J Dent. 1993 Feb;2 1 ( 1 ):47-5 1

42. Hacker CH, Wagner WC, Razzoog ME, Wagner WC et al. An investigation of

the Wear of enarnel on porcelain and gold in saliva. J Prosthet Dent 1996, 75: 14- 1 7.

43. Hamaguchi H, Cacciatore A, Tueller VM. Marginal distortion of the porcelain-

bonded-to-metal complete crown: an SEM study. J Prosthet Dent 1982; 47: 146- 153.

44. Hensten-Pettersen A. Casting alloys: side-effects. Adv Dent Res. 1 992 Sep;6:38-

43. Review

45. Holloway JA, Miller RB. The effect of core translucency on the aesthetics of ali-

cerarnic restorations. Pract Periodontics Aesthet Dent. 1997 Jun-Ju1;9(5):567-74

46. Holmes JR, Bayne SC, Sulik WD. Marginal fit of castable cerarnic crowns.

Journal of Dental Research 1992; 66: 283

47. Hung SH, Hung KS, Eick JD, Chappe11 RP. Marginal fit of porcelain-fùsed-to-

metal and two types of cerarnic crowns. J Prosthet Dent 1990; 63: 26-3 1.

48. International Organization for Standardization. Dental Materials - Testing of

adhesion to tooth structure, ISO/TS 1 1405/CD 1, 2000: 10.

49. Jacobs MS, Windeler AS, An investigation of dental luting cernent solubility as a

fùnction of the marginal gap. J Prosthet Dent 199 1 ; 65: 436-442.

50. Janenko C, Smales RJ. Anterior crowns and gingival health. Australian Dental

Journal 1979; 24: 225.

51. Jones D. Development of Dental Ceramics. Dental Clinics of North America

1985; 29(4):62 1-645.

52. Jorgensen KD. Factors affecting the film thickness of zinc phosphate cements.

Acta Odonto Scand 1960, 18,479.

53. Kay Gw, Jablonski Da, Dogon 11. Factors affecting the seating and fit of

complete crowns: a computer simulation study. J Prosthet Dent 1986; 55: 1 3- 18.

54. Katsuyarna S, Ischikawa T, Fuji B. Glass ionomer dental cement, the matenals

and their clinical use. Ishiyaku EuroAmenca Publishers, 1993.

55. Kelsey WP, Cave1 WT, Blankeneau RJ et al. Cyear clinical study of castable

ceramic crowns. Am J Dent 1995; 8: 259-262.

56. Krejci 1, Lutz F, Reimer M et al. Wear of cerarnic inlays, their enamel

antagonists, and luting cements. J Prosthet Dent. 1993 Apr;69(4):425-30.

57. Leempoel PJD, Eschen S et al. An evaluation of crowns and bridges in general

dental practice. J Oral Rehabil 1985; 12: 5 15-528.

58. Lehner CR, Scharer P. Al1 cerarnic crowns. Current Science l992,45-52.

59. Leung YC, Morris MD. Charactenzation of the chernical interactions between 4-

MET and enarnel by r ama spectroscopy 1995; 1 1 (3): 19 1 - 195.

60. Lillie RD, Corn's Biological Stains. 9h edition. Baltimore, MD: Williams &

Wilkins; 1977.

61. Lin MT, Sy-Munoz J, Munoz CA, Goodacre CJ, Naylor WP. The effect of tooth

preparation form on the fit of Procera copings. Int J Prosthodont 1998; 1 l(6): 580-90.

62. Lofstrom LH, Barakat MM. SEM evaluation of clinically cemented cast gold

restorations. J Prosthet Dent 1989; 6 1 : 664.

63. Lyons KM, Rodda JC, Hood JAA. Use of a pressure chamber to compare

microleakage of three luting agents. Int J Prosthodont 1997; 10 (5):426-433.

64. MacCulloch WT. Acivancçs in dental ceramics. Br Dent J. 1968 Apr

1 6; 1 24(8):36 1 -5.

65. Mahalick JA, Knap FJ, Weiter EJ. Occusal Wear in prosthodontics.

J Am Dent Assoc. 197 1 Jan;82(1): 154-9.

66. Malament KA, Socransky SS. Survival of Dicor glass-cerarnic dental restorations

over 14 years : Part 1. Survival of Dicor complete coverage restorations and effect of

intemal surface acid etching, tooth position, gender and age. J Prosthet Dent 1999; 8 1 :

23-32.

67. May KB, Russell MM, Razzoog ME et al. Precision of fit: The Procera AllCeram

crown. J Prosthet Dent 1998; 80: 394-404.

68. McLean JW. Evolution of dental cerarnics in the twentieth century. J Prosthet

Dent 2001; 85 (1): 61-66.

69. McLean JW, Hughes TH. The Reinforcement of Dental Porcelain with Ceramic

Oxides. Br Dental J 1965; 2 1 : 25 1-267.

70. McLean JW, Sced IR. Reinforcernent of aluminous dental porceiain crowns

using a platinum alloy preformed coping technique. Br Dent J. 1987 Dec 5;163(11):347-

52.

7 1. McLean JW, von Fraunhofer JA. The estimation of cement film thickness by an

in vivo technique. Br Dent J 197 1 ; 13 1 : 107- 1 1 1.

72. Meyers MI, Caughman WF, Rueggeberg FA et al. Effect of powdedliquid ratio

on physical and chernical properties of C & B Metabond. Am J of Dentistry 1993; 6: 77-

80.

73. Mitra SB, Conway WT. Coefficient or thermal expansion of some methacrylate-

modified glass ionorners. J Dent Res 1994; 73: 2 19.

74. Monasky GE, Taylor DF. Studies on the Wear of porcelain, enamel, and gold.

J Prosthet Dent. 197 1 Mar;25(3):299-306.

75. Moore JA, Barghi N, Brukl CE, Kaiser DA. Marginal distortion of cast

restorations induced by cementation. J Prosthet Dent 1985; 54 (3): 336-340.

76. Myers ML et al.: Marginal Leakage of Contemporary Cementing Agents. J

Prosthet Dent 1983, 50 (4): 5 13-5 15.

77. Nicholson JW. Chemistry of glass-ionomer cernents: a review. Biomaterials

1998; 19; 485-494.

78. Odén A, Rauoog ME. Masking ability of Procera AllCeram copings of various

thickness. J Dent Res 1997; 76: 3 10.

79. Odén A, Andersson M, Krystek-Ondracek 1, Magnusson D, Five-year clinical

evaluation of Procera AllCeram crowns. J Prosthet Dent 1998; 80: 450-456.

80. Oilo G, Evje DM. Film thickness of dental luting cements. Dent Mater. 1986; 2:

85-89.

8 1. Olgart L, Branstrom M, Johnson G. invasion into dental tubules. Experiments in

vivo and in vitro. Acta Odontol Scand 1974; 32: 6 1-70.

82. Omar R. Scanning electron microscopy of the marginal fit of ceramometal

restorations with facially butted porcelain margins. J Prosthet Dent. 1987 Ju1;58( 1 ): 13-9.

83. Ottle P, Piwowarczyk A, Lauer HC et al. The Procera AllCeram System. Int J

Periodontics Restoratice Dent 2000; 20 (2): 15 1 - 16 1.

84. Parneijer CH, Nilner K. Long term clinical evaluation of three luting materials.

Swed Dent J 1994; 18: 59-67.

85. Pashley DH. Clinical considerations of microleakage. J of Endodontics 1990; 16

(2): 70-77.

86. Patel S, Saunders W, Burke FJT Microleakage of dentin-bonded crowns placed

with different luting materials. Am J Dent 1997; 10: 179-183.

87. Persson M, Andersson M, Bergman B. The accuracy of a high-precision digitizer

for CADKAM of crowns. J Prosthet Dent 1995; 74: 223-229.

88. Peters MC, deVree JH, Brekelmans WA. Distributed crack analysis of ceramic

inlays. J Dent Res. 1993 Nov;72( 1 1 ): 1537-42.

89. Phillips RW Skinner's science of dental materials, g f h edition, 1982, W.B.

Saunders Company, Philadelphia, PA, USA 54.

90. Phillips RW, Swartz ML, Lund MS et al. in vivo disintegration of luting agents.

3 Am Dent Assoc 1987; 1 14: 489-492.

9 1. Probster L. Four year clinical study of glass-infiltrated, sintered alumina crowns.

J Oral Rehab 1 996; 23: 147- 1 5 1.

92. Ratledge Dk, Smith BG, Wilson RF. The effect of restorative materials on the

Wear of human enarnel. J Prosthet Dent. 1994 Aug;72(2): 194-203.

93. Rinke S, Huls A, Jahn L. Marginal accuracy and fracture strength of conventional

and copy milled al1 ceramic crowns. International J of Prosth 1995; 8: 303.

94. Rosenstiel SF, Gegauff AG. lmproving the cementation of complete cast

crowns : a cornparison of static and dynamic seating methods. J Am Dent Assoc 1988;

1 17 : 845-7.

95. Rosenstiel SF, Land MF, Crispin BJ. Dental luting agents: A review of the

current literature. J Prosthet Dent 1998; 80: 280-30 1.

96. Rosner D. Function, placement and reproduction of bevels for gold castings. J

Prosthet Dent 1963; 13 : 1 160- 1 166.

97. Sadoun M. Al1 Ceramic Bridges with the Slip Casting Technique 1998. 7'h

International Symposium on Ceramics, Paris.

98. Schwartz NL, Whitsett LD, Beny TG et al. Unserviceable crowns and fixed

partial dentures: life-span and causes for loss of serviceability. JADA 1970; 8 1 : 1395-

1401.

99. Scotti R, Catapano S, D'Elia A. A Clinical Evaluation of In-Ceram Crowns. Int J

Prosthodont 1 995; 8: 320-323.

100. Shiflett K, White SN. Microleakage of cements for stainless steel crowns.

Pediatric Dentistry 1997, 19(4): 262-266.

10 1. Sidhu SK, Watson TF. Resin-modified g l a s ionomer materials. Am J Dent

1995,8: 59-67.

102. Silness J. Periodontal conditions in patients treated with dental bridges. The

relationship between the location of the crown margin and the periodontal condition.

Journal of periodontal Research 1 970; 5: 225.

103. Silver M, Klein G, Fisher G. An evaluation and cornparison of porcelain fûsed to

cast metal. j Prosthet Dent 1960; 10: 1055.

104. Sjogren G, Lantto R, Granberg A et al. Clinical Examination of Leucite

Reinforced Glass Cerarnic Crowns (Empress) in General Practice : A Retrospective

Study. Int J Prosthodont 1999; 12 : 122-128.

105. Sorensen JA, Choi C, Fanuscu Mi et al. Empress Crown Systern: Three-Year

Clinical Trial Results. CDA Journal 1998; 26: 130-1 36.

106. Sorensen JA, Kang SK, Torres TJ et al. In-Ceram fixed partial dentures: three-

year clinical trial results. J Calif Dent Assoc. 1998 Mar;26(3):207- 14

107. Staninec M, Giles WS, Saiku JM et al. Caries penetration and cement thickness

of three luting agents. Int J Prosthodont 1988; 1 : 259-263.

108. Strating H, Pameijer CH, Gildenhuys RR. Evaluation of the marginal integrity of

cerarnometal restorations. Part 1. J Prosthet Dent 198 1,46 (1 ): 59-65.

109. Strub JR, Beschnidt SM. Fracture Strength of Five Different All-Ceramic Crown

Systems. Int J Prosthodont 1998, 1 1 : 602-609.

110. Sulaiman F, Chai J, Jameson LM, Wozniak WT. A Cornparison of the Marginal

Fit of In-Ceram, IPS Empress, and Procera Crowns. int J Prothodont 1997; 10: 478484.

1 1 1. Swartz, ML et al. Long tenn fluoride release fiorn glass ionomer cements. J Dent

Res 1984; 63 (2): 158-1 60.

1 12. Swartz ML, Sear C, Phillips RW. Solubility of cernent as related to time

exposure in water. J Prosthet Dent 197 1; 26: 501 -505.

1 13. Schwartz NL, Whitsett LD, Berry TG et al. Unserviceable crowns and fixed

partial dentures: life span and causes for loss of serviceability. J Am Dent Assoc 1970;

81: 1395-1401.

1 14. Ten Cate JM, Van Duinen RNB. Hypermineralization of dentinal lesions

adjacent to glass-ionomer cement restoration. J Dent Res 1995; 74: 1266- 127 1.

1 15. Tjan AFL, Chiu J. Microleakage of core materials for cornpiete cast gold crowns.

J Prosthet Dent 1989; 6 1 : 659-664.

1 16. Tjan AHL, DUM JR, Grant BE. Marginal leakage of cast gold crowns luted with

an adhesive resin system. J Prosthet Dent 1992; 67: 1 1 - 15.

1 17. Tjan A, Li T. Retention and fit of crowns cemented with an adhesive resin. J

Dent Res 1 990; 69; 1 23.

1 18. Tjan AHL, Miller GD, Whang SB, Sarkissian R. The effect of thermal stress on

the marginal seal of cast gold full crowns. JADA, 1980, 100; 48-5 1.

1 19. Tuntiprawon M. Effect of surface roughness on marginal seating and retention of

complete metal crowns. J Prosthet Dent, 1999; 8 1 : 142- 147.

120. Tuntiprawon M, Wilson PR, The effect of cernent thickness on the fracture

strength of all-ceramic crowns, Aust Dent J 1995 40( 1 ): 1 7-2 1

12 1 . Vahidi F, Egloff ET, Panno FV. Evaluation of marginal adaptation of all-

ceramic crowns and metal ceramic crowns. J Prosthet dent 199 1 ; 66: 426-43 1 .

122. Valderrama S, Van Roekel NV, Andersson M et al. A cornparison of the

marginal and intemal adaptation of titanium and gold-platinum-palladium metal ceramic

crowns. [nt J Prosthodont 1995; 8: 29-37.

123. Valderhaug J, Birkeland JM. Periodontal conditions in patients 5 years foilowing

insertion of fixed prostheses. J Oral Rehabil 1976; 3: 237-243.

124. van der Vyver PJ, de Wet FA. The film thickness of five adhesive resin cements.

South Afncan Dental Journal 1998; 53: 377-379.

125. Van Rensburg F, Strating H. Evaluation of the marginal integrity of cerarnometal

restorations: Part II. J Prosthet Dent. 1984 Aug;52(2):2 10-4.

126. Vargas MA, Cobb DS, Armstrong SR. Resin-dentin shear bond strength and

interfacial ultrastructure with and without a hybrid layer. Oper Dent 1997;22: 159- 166.

127. Wagner WC, Chu TM. Biaxial flexural strength and indentation fracture

toughness of three new dental core ceramics. J Prosthed Dent 1996; 76: 140-4.

1 28. Walton JN, Gardner FM, Agar JR. A survey of crown and fixed partial denture

failures: length of service and reasons for replacement. J Prosthet Dent 1986; 56 (4):

416-421,

129. Wang CJ, Millstein PL, Nathanson D. Effects of cement, cernent space, marginal

design, seating aid materials and seating force on crown cementation. J Prosthet Dent

1992; 67: 786-90.

130. Wataha JC, Hanks CT. Biological effects of palladium and nsk of using

palladium in dental casting alloys. J Oral Rehabil. 1996 May;23(5):309-20

13 1. Weaver JD, Johnson GH, Bales DJ. Marginal Adaptation of Castable Ceramic

Crowns. J Prosthet Dent 199 1 ; 66 (6): 747-753.

132. Wendt SL, McInnes PM, Dickinson GL. The effect of thermocycling in

microleakage analysis 1992; 8: 18 1 - 184.

133. White JM, Goodis HE, Marshall SJ, Marshall GW. Sterilization of teeth by

gamma radiation. J Dent Res 1994, 73(9): 1 560- 1 567.

134. White SN, Furuichi R, Kyomen SM. Microleakage through dentin afier crown

cementation. J Endod 1995; 2 1 : 9- 12.

135. White SN, Ingles S, Kipnis V. Influence of marginal opening on microleakage of

cemented artificial crowns J Prosthet Dent 1994; 7 1 : 257-264.

136. White SN, Kipnis V. Effect of adhesive luting agents on the marginal seating of

cast restorations. J Prosthet Dent 1993; 69: 28-3 1.

137. White SN, Yu 2, Tom JF, Sangsurasak S. In vivo microleakage of luting cements

for cast crowns. J Prosthet Dent 1 994; 7 1 : 333-338.

138. White SN, Sorensen JA, Kang SK. hproved marginal seating of cast

restorations using a siliconedisclosing medium. 199 1 ; int J Prosthodont; 4: 323-326.

139. White SN, Sorensen JA, Kang SK, Caputo AA. Microleakage of new crown and

fixed partial denture luting agents J Prosthet Dent 1992; 67: 1 56- 16 1.

140. White SN, Yu 2, Tom J et al. In vivo marginal adaptation of cast crowns luted

with different cements 1995; 74:25-32.

141. Whitlock, R. P., Tesk, J. A., Widera, G. E. O., Holmes, A., and Parry, E. E.

Consideration of some factors influencing compatibility of dental porcelains and alloys.

Part 1. Thermo-physical properties. pp. 273-282. In Proc. 4th int. Precious Metals

Conference, Toronto, June 1980. Willowdale, Ontario: Pergamon Press Canada, Apnl

1981.

142. Wilder ADJ, May KN, Swift EJ, Sulilvan DJ. Effects of viscosity and surf'ace

moisture on bond strengths of resin-modified glass ionomers. Am J Dent 1996; 9 (5):

215-218.

143. Wilson AD, Kent BE. A new translucent cernent for dentistry. The glass

ionomer cement. Br Dent J 197 1 ; 132 (2): 133- 135.

1 44. Wilson AD. Resin-modi fied-glass-ionomer cements. Int J Prosthodont 1 990; 3

(5): 425-429.

145. Xu HH, Jahnmir S. Simple technique for o b s e ~ n g subsurface damage in

machining of ceramics. J Am Ceram Soc 1994; 77: 1388- 1390.

1 46. Yoshinari M, Derand T. Fracture strength of all-ceramic crowns.

int J Prosthodont. 1994 Jul-Aug;7(4):329-38.

147. Zeng K, Odén A, Rowcliffe D. Flexure tests on dental cerarnics. Int J

Prosthodont 1996; 9: 434-439.