A Comparison of theMarginal Fit of

In-Ceram, IPS Empress,and Procera Crowns

Frankie Sulaiman, DDS, Al:

lohn Chai, BDS, MS, Mj''

Lee M. Jameson, DDS, MS'

Wayne T. Wozniak, PhD''

The in vitro marginal fit of three all-ceramic crown systems (In-Ceram,Procera, and IPS Empress) was compared. All crown systems weresignificantly different from each other at P- 0,05, In-Ceram exhibited tliegreatest marginal discrepancy (1 bl pm), followed by Procera ¡83 |jm¡, andIPS Empress (63 ¡Jm), There were no significant differences among thevarious stages of the crown fabrication; core fabrication, porcelain veneering,and glazing. The facial and lingual margins exhibited significantly largermarginal discrepancies than the mesial and distal margins, ¡nt j Proslhodortt1997; 10:478-434.

A li-ceramic dental restorations provide estheticsseldom rivaled by metal ceramic restorations.

One all-ceramic system is fabricated using a slip-casttechnique {In-Ceram, Vita Zahnfabrik)'"^ and anotherby a heat-press technique (IPS Empress, Ivoclar).^-''

Slip casting is a technique derived from industrialtechnology and adopted for dental use,' The slip-cast alumina is firsf partially sintered in a furnace,producing a porous framework that is then infil-trated with liquid glass in a second firing process.Crack propagation during failure is limited becauseof the densely packed alumina particles. Class infil-tration eliminates almost ail porosities, which are

'CrsduMe. Advanced Fducation Froithodonlics. NorlhweiternUniversity Dental School. Chicago. Illinois.

''Assistant Professor and Director, Advanced EducationProsthodontics, Northwestern University Denial School,Chicago. Illinois.

"^Professor and Chairman. Department of Restorative Dentistry,Northwestern University Dentai School. Chicago, Illinois

''Director. Evaluations and Criteria, Council on ScientificAffairs. American Dental Association, Chicago, iliinois.

Reprints requests: Dr ¡ohn Chai, Assistant Professor and Director.Advanced Education Prosthodontics. Northwestern UniversityOentai Schooi. 240 East Huron Street. Chicago. Illinois 60611.

potential sites for crack initiation. The difference inthe coefficients of thermal expansion between alu-mina and glass produces compressive Stresses at thealumina-glass interface that further enhancestrength. Several studies bave shov\'n tbat a glass-infiltrated alumina crown may achieve a strengththree to four times greater than the strength of ear-lier alumina core materials,'""'^ The marginal in-tegrity of this system has also been evaluated,'-"'^

High-strength cores are also fabricated with aheat-press technique (IPS Empress)/-" A feldspathicporcelain consisting of 63% SiO^ and 18% AI^O^ isused as a basic material. In addition, leucite crystalsare used as the crystalline part of the ceramic, Acomplete contour wax pattern for the restoration isplaced on a specially designed cylindrical crucibleformer and invested in a phosphate-bonded invest-ment. After the temperature of the mold basreached 850°C in a wax elimination furnace, a ce-ramic ingot and an AI^O^ pushing rod are placed inthe mold. The cast is immediately preheated in theautomatic press furnace (1150°C) (Empress EP 500,Ivoclar), and the plastic glass-ceramic material ispressed into tbe mold. Surface characterization maybe performed to achieve the desired shade, -^ This

Tlie Inte manorial lournal of Proslliodonlii 478

Sula msii e( .i! Miir^inai Fil of In-Ceram, IPS Empress

Table 1 Marginal Discrepancy of Various Crown Systems

nvesti gators

Chan et at

FerrariAbbate et al

Grey et al

Pera et al

Sorensen et alRinke et al

Janenko and SmalesFelton et alOrnarStrati ng et al

Boyle et al

Leong et al

Baez et alBlackman et alKrejci et al

Reference

35

3637

12

13

1415

31283B39

40

41

424344

Material

Cemented Cerestore crownsUncemented Cerestore crownsDicor castable ceramic crownsMetal tacial metal ceramic crownsPorcela n facial melal ceramic crownsCerestore crownsDicer crcwnsIri-Ceram crownsPorcela n jacket crownsMetal ceramic crownsChamter margin In-Ceram crowns50-degree shoulder In-Ceram crowns90-degree shoulder In-Ceram crownsIn-Ceram copingsIn-Ceram conventional mettiodIn-Ceram copy-milling methodPorcelain jacket crownsMetal ceramic crownsMetal ceramic crownsMetal collar porcela in-fused-to-metal crownsCollarless porcelain-f used-to-metal crownsFacial porcelain margin metal ceramic crownsMetal ceramic facial margins crownsMetal ceramic shoulder porcelain crcwnsVita SM 90 porcelain orownsMachineö-milled titanium metal ceramic crownsCast titanium metal ceramic crownsNcble alloy metal ceramic crownsTitanium crownsTitanium copings risoESBassm-IPS Empress inlays

and Procera Crowns

Mean marginaldiscrepancy |ijm¡

84 ±4475 ± 3715-75 (range)60.6 ± 26.4 '"57 ±24.244.1 ±1265.3 ± 17.5123 ±30154 ±3795 ±2321.67±2.1723.75 ±2.07 '•.'27.50 ±3.1324-67 ¡range]1-153 (range) 'I6-153 (range) 'J'^154 ±905-430 (range) .i.'i76 ±211623.669 . .^13.78.211 354 ± 65 aawsBffii^60 ± 42 ^ 'ff.25 ± 40 'I7-100 (range)507B.2±15.1

core material possesses a high flexural strength inthe range of 160 to 220 MPa.^^^^

A new method of fabricating all-ceramic restor-ations was recently introduced as the Proceratechnique (Procera Sandvik). A densely-sintered,high-purity alumina ( A l p , > 99-9%) is used in thetechnique. This same material has been used in aceramic core for singie-tooth Implant replacement(CeraOne, Bránemark system, Nobel BioCare) andin a ceramic abutment for implant-supported singlecrowns (CerAdapt, Bránemark system, NobelBioCare)-i5-° The working die is first digitized inthree dimensions- A duplicate of this die is thenproduced with a 12% to 20% enlargement usingcomputer-aided design-computer aided machining(CAD-CAM) technology. High-purity alumina pow-der is compacted onto the enlarged die using a drypressing technique,-' The coping is tben sintered at155O°C for 1 hour. It is then adjusted, ground, pol-ished, and thermal-etched before porcelain applica-tion- Because of its high alumina content, the corematerial maintains a flexural strength of 650 MPa-^-In one study, the Procera all-ceramic crown (687MPal was found to have a 95% and 413% bighermean strength than the In-Ceram (352 MPa] and IPS

Empress (134 MPa) crowns, respectively," In addi-tion to mechanical strength, the characteristics ofenamel wear'-* and indentation fracture toughness^^of the Procera all-ceramic have also been studied-

Marginal adaptation is one of the important criteriaused in the clinical evaluation of fixed restorations.The presence of marginal discrepancies in therestoration exposes the luting agent to the oral envi-ronment. The larger the marginal discrepancy andsubsequent exposure of the dental luting agent tooral fluids, the more rapid is the rate of cement disso-lution.^^ The resultant microieakage permits the per-colation of food, oral debris, and other substancesthat are potential irritants to the vital pulp." Thelongevity of the tooth could be compromised, notonly by caries, but also by periudontal disease, ''' ^Clinical studies have shown that poor marginal adap-tation of a restoration correlates with increasedplaque retention and reduced gingival health, as in-dicated by a higher Plaque Index (PI), an elevatedGingival Index (CD, and increased pocket depthsIPD).^*'-'' A change in the subgingival microflora isalso attributed to inadequate marginal adaptation.'"

The marginal discrepancy of various restorationshave been studied (Table 11.^'-"^ In-Ceram crowns

Volume 10, Number S, 1997 479 The Intemalional lournal of Pn

Marymal Fit ol Ir.Cerjm, IPS Em|)rms, und Pr(

varied from a mean marginal discrepancy of 22 [tmfrom one study'-* to 123 pm in another study.'^ Anin vitro study showed that IPS, Empress inlays havea mean marginal discrepancy of 78 pm. FHowever,to the authors' knowledge no data are available onthe Procera all-ceramic crowns.

Marginal distortion of metal ceramic restora-tions during various stages of fabrication is well-documented,"'''"''' The authors are unaware of anystudy that has been conducted to examine the ef-fect of porcelain application on the marginal dis-crepancy of all-ceramic restorations.

The purposes of the study were to compare:

1, The marginal discrepancies of three all-ceramiccrown systems at various surfaces of the restora-tion: mesial, distal, buccal, and lingual. The all-ceramic crown systems studied were the denselysintered high-purity alumina porcelain crown(Procera Sandvik), the heat-pressed feldspathicglass-ceramic crown (IPS Empress), and the slip-cast sintered alumina ceramic crown (In-Ceram),

2. The marginal discrepancies of these three all-ceramic systems at various Stages of fabrication:at fabrication of the core material, after the ap-plication porcelain veneer, and after glazing.

Materials and Methods

An all-ceramic crown preparation of a maxillarycentral incisor was fabricated in a base metal alloy(Rexillium, Jeneric Pentron). Tbe preparation fol-lowed commonly used textbook guidelines,-^ Themetal die was polished, and the marginal integrityof the die was carefully examined under a micro-scope. Four vertical lines were scribed onto the dieapproximately 0,5 mm below the margin on themidmesial, midbuccal, midpalatal, and middistalsurfaces using a 0,25-mm round carbide bur.These vertical lines were used to help orient thedigital microscope for the marginal discrepancymeasurement, A poly(vinyl siloxane) index (Putty,Reprosil, LD Caulk, Dentsply] was fabricated usinga complete contour wax pattern on the die. Thisindex was used to facilitate porcelain applicationso that the dimensions of the crowns would be rel-atively identical.

Impressions of the master die were made usingpoly(vinyl siloxane) (Light-body and Putty,Reprosil) in custom trays. A total number of 30 im-pressions were made and poured using type IVdental stone (Silky-Rock, Whip Mix). The stonedies were divided into three groups of 10 dieseach: Procera (Procera Sandvik) crowns; IPSEmpress (Ivoclar) crowns; and In-Ceram (Vita

Zahnfabrik) crowns. All crowns were fabricated ac-cording to their respective manufacturer's recom-mendations.

The Procera crowns were fabricated by ProceraSandvik in Göteborg, Sweden, The IPS Empresscrowns were made by a commercial laboratory cer-tified in the technique. The In-Ceram copings wereprovided by Vident in Baldwin Park, California, andthe porcelain veneering and glazing were per-formed by the in-house laboratory at Northwesterntjniversity Dental School,

The marginal fit of each restoration was exam-ined at 225 X magnification using a digital micro-scope (Nikon SMZ-U, Nikon), The calibrated springof a 2-inch C-clamp held the restoration onto themaster die with a standardized force of 3 Ib (1.36kg) when the spring was completely compressed.This force was estimated to be the mean force toseat a restoration,^- The spring had been previouslycalibrated by plotting the force and the length of thespring on a universal testing machine (Instron).

All measurements were made on the master die.The marginal fit of each restoration was measuredafter the following stages of fabrication: (1) at fabri-cation of the core material, (2) after dentin andenamel porcelain applications, and (3) after glaz-ing. At each stage, four points on each restorationwere measured: midbuccal, midmesial, midlin-gual, and middistal.

An angle level was used to ensure that the sam-ple was perpendicular to the objective lens of themicroscope during each measurement. Each sur-face was measured three times, and the meanvalue was obtained, resulting in 360 measurementsfor each stage of fabrication. The images were thenidentified and printed. The digital microscope wascalibrated with the use of an objective micrometer(American Optical) prior to the experiment. All themeasurements were made by one operator. To de-termine the consistency of the measurements of theoperator, one randomly selected restoration wasplaced on tbe master die, and one randomly se-lected surface was measured 30 times. The mea-surement showed a standard error of 2,84 (jm witha confidence level of 1.01 pm. This result wasdeemed acceptable for the purpose of the study,

A three-way analysis of variance (ANOVA) wascomputed for statistical significance among tbreevariables at P = 0,05: (1) the crown systems, (2) thesurfaces, and (3) the stages of fabrication, A Tukeypost hoc analysis was used to evaluate the significantdifference between interactions. The clinical rele-vance of the results was interpreted by comparisonwith the acceptable marginal discrepancy of 120 pmas proposed by McLean and von Fraunhofer.^^

The IntemationjI lournal of Pro5thocluntii 480 Volume 10, NurDbei5, 1997

Marginal Fit ol In-Ceram, IPS Empress, and Procera Crow

Results

Three-way ANOVA revealed significant differencesamong the three ceramic systems, among the vari-ous surfaces, and among the system-surface inter-actions t.P < 0.05) (Table 2). There were no signifi-cant differences in the marginal discrepanciesamong the three stages of porcelain applications(P> 0.051 (Table 2). One-way ANOVA and Tukeypost hoc analysis showed that the In-Ceram grouppossessed significantly larger marginal discrepancythan either the Procera group or the IPS Empressgroup (P < 0.05). The Procera group had signifi-cantly larger marginal discrepancy than the IPSEmpress group (P < 0.05) (Table 3|. The mean mar-ginal discrepancy of the Procera group and the IPSEmpress group at 82.88 and 62.77 |jm, respec-tively, met the criterion of an acceptable marginaldiscrepancy at 120 pm.^^ The mean marginal dis-crepancy of the In-Ceram group at 160.66 [jm ex-ceeded the 120 [jm criterion.

The one-way ANOVA and Tukey post hocanalysis showed that the lingual location had a sig-nificantly greater marginal discrepancy than eitherthe mesial or the distal locations (P < 0.05). Themarginal discrepancy at the lingual location wasnot significantly different from the facial discrep-ancy (P> 0.05) (Table 4|.

Table 5 depicts the marginal discrepancies of thethree crown systems at each marginal location. Allmarginal locations of the Procera group and theIPS Empress group met the ! 20-|Jm criterion; how-ever, all margin locations of the In-Ceram groupfailed to meet this criterion.

Discussion

That significant differences were found among thesystems but not at the various stages of fabricationsuggested that the ceramic coping fabrication ac-counted for the different marginal discrepancy ofthe ceramic systems. Fabrication of the Procera all-ceramic restoration requires digitization of thestone die. The data input are determined by thesensitivity of the probe, which has a maximumshape-related error of 10 pm in a complete revolu-tion.^-' The maximum error encountered from theprobe and the milling process has been shown tobe less than 100 (jm.'-* The dimension of the stonedie is mathematically recalculated to fabricate theenlarged refractory die. Therefore, the dimensionof the refractory die is determined by the accuracyand the precision of the computer software.-'

To fabricate a Procera ceramic coping, a densesintered aluminum oxide powder is compacted

Table 2 Ttiree-Way ANOVA of Data

System'StageSurface"System x StageSystem \ Surface'Stage x SurfaceSystem x Stage x Surface

'Marked eftects sianiticant at P <

184.13051.696487.284812.11865.33050.106380.2840

0 05.

0.000000.182770.000240.077020.000000.994280.99097

Table 3 Means and Standard Deviations ot theMarginal Discrepancies of Three Ceramic Systems

System n fiflean S

ProceraIPS Empressin.Ceram

120120120

32.8862.77

160.66

41.4537.3245 98

All systems are significantly different from each othe•ne-way ANOVA and Tjkey post hoc test

at P=0.Q5 using

Table 4 Means and Standard Deviations of theMarginal Discrepancies at Four Marginal Locations

Surface fulean SD

FacialfvlesialLingualDistal

102.5496.11

124.3885.39

48.1662.0763.0456.79

Vertical bars indicate siatiîticsily signrficant difference between pairs atP - 0.05 using Tukey post hoc test.

Table 5 Means and Standard Deviations of ThreeCeramic Systems on Various Surfaces

System

Procera

IPS Empress

In-Ceram

Surface

FacialMesialLingualDistalFacialMesialLingualDistaiFacialMesiaiLingualDistal

fvlean

66.7993.49

103.5467.7186.8042 3676.8045.13

154.02152.48192.80143.32

SD

22.3341.0041.3545.8029.70

35.2437.4225.3337.6551.1938.1141.13

•10, Njmber 5,1997 481 The Internafioral loumal of Proslliodontics

Marymal Fit oí livCe

onto the refractory die. The amount of shrinkage ofthe aluminum oxide powder is compensated bythe enlarged refractory die,^- Information on themagnitude of the firing shrinkage of the aluminumoxide powder and the percentage enlargement ofthe refractory die is not available from the manu-facturer, A mistake in compensating the amount ofshrinkage would result in poor adaptation of thecoping onto the stone die''" and thus compromiseits marginal integrity,''^

The lost wax technique is used for the fabrica-tion of IPS Empress copings. The wax pattern isfabricated on a stone die with die spacer applied,^^The thickness of the die spacer recommendedranges from 25 to 40 \im.^^ Shrinkage of 0.4% canbe expected from the wax pattern upon cooling atroom temperature,^" Thermal shrinkage of approxi-mately 0,2%^' of the ceramic coping is also ex-pected after casting. This thermal shrinkage is com-pensated by setting and thermal expansion of aphosphate-bonded investment at approximatelyO,3%5« and O,27ci," respectively. Thus, the net di-mension of a cast ceramic coping is the result ofthe expansion and contraction of various materialsused in its fabrication. The intricate balance andcontrol of the materials are necessary for an ac-ceptable fit.

The fabrication of the In-Ceram aluminous corerequires two stages: condensation of the aluminumoxide powder onto the refractory die followed by aglass-infiltration process. Aluminum oxide powderis applied onto the refractory die and fired in a spe-cial furnace at 11 20°C, The aluminous substructureas fabricated is fragile, and careless removal of ex-cess material at the margin could potentially leadto increased marginal discrepancy.•'•''•'- During theglass-infiltration firing, the glass mixture tends logravitate, and it creates an excessive bulk at themargin of the coping after the firing is completed'^and must be trimmed using a rotary instrument.This procedure must be performed extremely care-fully to maintain marginal integrity.

The error incurred at each step of the fabricationof an all-ceramic system would either compound oroffset previous errors. Although the number of stepsinvolved in the fabrication of all-ceramic crownswas not a direct indication of the quality of the mar-ginal integrity, one may suggest that the more thesteps involved and the more sensitive the tech-niques, the more likely it is that technical errors willoccur. The results of this study suggest that themean marginal discrepancy of the all-ceramic sys-tems follows in descending order: In-Ceram,Procera, and IPS Empress. The differences amongthe systems are attributed to the coping fabrication.

This could be partially explained by technique sen-sitivity and the number of the steps in fabricatingthese copings.

The lingual margin of the all-ceramic crownsshows significantly higher marginal discrepancythan other surfaces. This may be explained by tbelarger amount of firing shrinkage at the lingual sur-face. Although it was not the initial intent of thisstudy to investigate the relationship between themarginal discrepancy and the bulk of the porcelainaround the margin, a measurement of the thicknessof the all-ceramic crown shows the lingual bulk tobe approximately 20% thicker than otber areas.Since firing shrinkage is a function of the porcelainbulk,*"^ it is possible that the larger marginal dis-crepancy seen at the lingual margin could be re-lated to the greater bulk of porcelain.

The mean marginal discrepancy of 161 fjm of theIn-Ceram crowns in this study was not in agreementwith the finding of Pera et al,'^ who found a meanglass-ionomer cement thickness for In-Ceramcrowns on epoxy resin teeth in the range of 15 to35 fjm, Sorensen et al'"" reported the mean marginaldiscrepancy of cemented In-Ceram crowns to be inthe range of 24 to 67 pm with various designs ofpreparation, Rinke et aP^ also found that the mar-ginal discrepancy of cemented In-Ceram crownsranged from 1 to 153 pm (median 32,5 fjm) with aconventional technique, and from 3 to 153 [im(median 38 pm) with a copy-milled technique.Conversely, Crey et al'^ found the mean cementspace thickness of In-Ceram crowns to be 123 pm.An explanation of the lack of agreement is the vari-ation in the method used by various investigators instudying marginal discrepancy. In contrast to thepresent experiment in which a digital microscope(x 225 magnification) was used, others have used adigital microscope (magnification not reported) tomeasure the sectioned teeth,'"* a stereomicroscope¡X 100 magnification),^^ and a light microscopeconnected to a computer monitor (X 180 magnifi-cation)'^ for direct measurement.

The current findings on the IPS Empress crownsin this study (62.77 ± 37,32 fjm) agrees with thosefindings on IPS Empress inlays by Krejci et al,''''who reported tbe value in the range of 62,3 to101,0 pm (mean 78,2 ± 15,1 fjm).

In an attempt to correlate the results of this studywith published clinical studies, the authors canonly find incomplete or short-term clinical data. Ina study that evaluated the clinical outcome of IPSEmpress inlays, the percentage of gap-free inlaysdecreased from 97,4% to 66,8% over a 1,5 yearobservation period,'*'' Two clinical studies of theIn-Ceram crowns did not reveal the results on the

482

Margin,)! FU ol Iii-Ceram, IPS Empress, and Procera Crown;

quality of the marginal adaptation."-^" To the au-thors' knowledge, no in vitro or in vivo data areavailable for comparison with the Procera crownsin this study. Further investigation is necessary toexamine the clinical outcome of these all-ceramicrestorations.

Conclusions

Thirty all-ceramic restorations were fabricated andmeasured for the marginal integrity during variousstages of fabrication. Within the conditions andlimitations of tbis study, the following conclusionsmay be drawn:

1. Tbe mean marginal discrepancy of tbe all-ceramic crowns was. in descending order: In-Ceram (161 ± 46 |jm). Procera (83 ± 41 pm),and IPS Empress (63 ± 37 pm|. Both Proceraand IPS Empress met the criterion for accept-able marginal discrepancy of 120 \im.

2. The lingual surfaces of the ceramic crowns pos-sessed significantly greater marginal discrepan-cies than all other surfaces. There were no sig-nificant differences among the other threesurfaces: facial, mesial, and distal.

3. For all three all-ceramic systems, no significantdifference in marginal discrepancy was observedduring the various stages of fabrication: core fab-rication, porcelain veneering, or glazing.

Acknowledgments

The aulhori would like to express Iheir thanks to the following:Nobel BioCare AB, Göteborg, .Sweden—Dr Robert Gortlanderand (he people involved in fabricating the Procera all-ceramicrestoralions^ Nobel BioCare USA, Westmont, Illinois—DrBjarne Kvanstrom, Ms Anna Letsos, and Ms Kathleen Maikefor rendering tremendous help in using the digital micro-scope; Lords Denial Studio, Green Bay, Wisconsin—Kris vanLaanen and his colleagues for their help in fabricating the IPSEmpress all-ceramic restorations: Vident USA, Baldwin Park,California—Ray Marrow and Christ Herzog for iheir help andsupport in fabricating the In-Ceram copings: Central Laboratory,Northwestern University Dental School—Robert Borek, CDT,and loyce Teleback, CDT.

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Erratum

Please note the following correclion to the article "Implant-Supported Overdenture Rehabilitation and ProgressiveSystemic Sclerosis" by Ravivetal (Int J Prosthodont 1996;9:440-444). The authors would like to acknowledge DrRonald M Fisher's contribution to the prosthodontio treatment of the case presented. As an instructor in charge of re-movable prosthodontics, Dr Fisher supervised the resident that treated the patient. The authors regret their failure toacknowledge Dr Fisher in the original article.

I UÍ Proslhodontii 484 ne ID, Number 5, 1997