Marginal Adaptation ofPorcelain Margins in Metal

Ceramic Restorations

Nancy R. Chaäee, DDS, MS"

Peter S. Lund, DDS, MS""

Steven A. Aquilino, DDS, MS""

Ana M, Diaz-Arnold, DDS, MS"""'

University of Iowa College of Dentistryiowa City. Iowa

The purpose of this study was to evaluate the marginaladaptation of all-porcelain labia! margin metal ceramiccrowns using a porcelain shoulder material containing alight-polymerizing resin and one that used a direct-lifttechnique. Conventional metal margin restorations served ascontrols. Scanning electron micrographs were made of a 1-mm mesiodistal width of the margin at midfacial andmidlingual reference marks. Image processing and analysistechniques were accomplished using a computer. Statisticalevaluation indicated that the mean labial marginaldiscrepancy of the control group was significantly less thanthat of either of the two porcelain shoulder methods. Int IProsthodont 1991,-4:508-516,

T he all-porcelain labial margin metal ceramicrestoration has proven to be a viable alternative

to the conventional metal ceramic restoration inesthetically demanding restorative situations. Pre-viotis comparison studies have shown that the mar-

'Formerly Graduate Student. Department oí Prosthodontics,University of Iowa; Currently Assistant Proiessor. Sectionoí Restorative and Prosthetic Dentistry. Ohio State Uni-versity.

"Assistant Professor, Department of Prosthodontics,"""Associate Professor, Department of Prosthodontics.

"^Assistartt Proiessor, Department of Family Dentistry.

Reprint requests: Dr Nancy R. Chafíee, Ohio State UniversityCollege of Dentistry, 3005-U Postle Hall. 305 W 12th Avenue,Columbus, Ohio 43210-1241.

Based on a thesis submitted to the Graduate College, Uni-versity of Iowa, in partis! fulfiilment of the requirements forthe Master of Science degree in Prosthodontics.

Winner of the lADR Prosthodontics Research Croup Arthur R.Frechette Novice Award, Presented at the lADR 69th GeneralSession/AADR 20th Annual Session. April 20, 1991, Acapuico,Mexico.

ginal adaptation of the all-porcelain labial marginmetal ceramic restoration is technique sensitive.'•'Variability in the marginal adaptation can resultfrom the porcelain binder as well as the fabricationtechnique used for this restoration.^" The intro-duction of light-polymerized resin as the binder forthe porcelain may make fabrication of these res-torations easier.'^ However, the final marginaladaptation of these crowns has yet to be reported.

The purpose of this study was to evaluate theadaptation of the porcelain and metal margins ofall-porcelain labial margin metal ceramic restora-tions fabricated using light-polymerized resinbinder m a direct-lift technique. The marginaladaptation of these restorations was compared torestorations fabricated using a traditional direct-liftall-porcelam margin technique employing shoulderporcelain, as well as to metal margin metal ceramicrestorations which served as the control specimens(Table J).

Materials and Methods

A dentoiorm replica of a maxillary right centralincisor (Kilgore International, Coldwater, Mich) was

The International Joumal of Proirhodontics 508 Volume 4, Number 6, 1991

Porceiain Margins ir Metal Ceramic Restorations

prepared for a metal ceramic restoration. The labialmargin configuration consisted of a 90° cavosur-face shoulder margin 1.5 mm in width withrounded internal line angles (Figs 1 and 2). Inter-proximally, the shoulder blended into a lingualchamfer finish line. Reference marks were pre-pared approximately 2 mm cervical to the midfacialand midlingual cavosurface margins of the pre-pared tooth using a % round bur. The mesial rootsurface was milled to provide a fiat surface toenable alignment of the tooth on a scanning elec-tron microscope mounting plate. Thirty replicas ofthe prepared tooth were fabricated by the manu-facturer for use as master dies.

Impressions of the master dies were made usinga low-viscosity poly(vinyl siioxane) impressionmaterial (Mirror 3 Fxtrude, Kerr Manufacturing Co,Romulus, Mich] in phenolic rings (Buehler Ltd,Lake Bluff, III). Stone working dies were fabricatedusing a vacuum-mixed improved dental stone(Die-Keen, Columbus Dental, St Louis, Mo) usingthe manufacturer's recommended water/powderratio.

Three coats of die spacer (Tru-Fit Die Relief,George Taub Products and Fusion Co, Jersey City,N|) were applied to witbin 1 mm of the margin ofthe working dies. Wax patterns for the copingswere fabricated using wax and a dip technique

Table 1 Porcelain Systems

Group Technique

A Light-poiymerizeddirect-lift ali-porceiainmargin

B Traditionaldtrect-lift ail-porcelainmargin

C Conventionalmetal collarmargin

Product

Spectrum(Cpaque 053,Opaque Medium,Dentine B53,Enamel E41,Porcelain Medium,VLC ShouiderPorcelain LRB)

Vita VMK 68(Opaque 21.Dentine 241,Ënamei 258,Shoulder 294.30M ModelingLiquid)Vita VMK 68{Opaque 211.Dentine 241,Enamel 258,30M ModelingLiquid)

Manufacturer

Dentsplyinternational

York, Pa

VidentVita ZafinfabrikBaidwin Park,

Caiif

VidentVita ZahnfabrikBaldwin Park,

Calif

{Dura Dip Wax, Belle de St Claire, Van Nuys, Calif).The lingual contour, facial metal collar, and finalmarginal adaptation were completed using blue

Fig 1 (Left) Master diewith dimensions (mm) oftooth preparation (labialview).

Rg 2 (Right) Master diewith dimensions (mm) oftooth preparation (próxi-ma i view).

Volume 4, Number 6, 1991 509 The international Journai of Prosltiodontics

Porcelain Margin* in Metal Ceran

Fig 3 Wax pattern.

inlay wax (Kerr Manufacture tig Co) as shown in Fig3.

The wax patterns were invested using a phos-phate-bonded investment ¡High Span II, ]elenkoDental Health Products, Armonk, NY) and cast in

a gold-palladium alloy (Cameo, Jelenko DentalHealth Products) using an induction castingmachine (Autocasl Digital Induction Casting Unit,Unitek Corp, Monrovia, Calif). The castings werecleaned using 60 ^m aluminum oxide air abrasive

Fig 4 (Lett) Metal coping,labial collar reduced.

Fig 5 (Right) MsXs\ cop-irig with labial collar.

The International Journal of Prostliodoniics 5 1 0 Volume 4, Number 6, 199!

and finished using aluminum oxide stones to obtaina uniform metal coping thickness of 0.4 mm. Theareas not to be veneered were finished with burlewwheels.

Visual verification was used to adjust the metalcopings to fit the working dies. The 30 copingswere then randomly assigned to one of threegroups for fabrication of restorations; group A, ametai ceramic restoration with an all-porcelainlabial margin fabricated using a visible-light-polymerized shoulder porcelain in a direct-lifttechnique; group B, a metal ceramic restorationwith an ali-porcelain labial margin fabricated usinga shoulder porcelain in a direct-lift technique; orgroup C, a conventional metal collar metal ceramicrestoration. The facial collar, which had beenwaxed and cast, was removed to the gingivoaxialline angle with an aluminum oxide stone on thecastings of the all-porcelain margin groups (Fig 4).The facial collar of the control group specimenswas reduced to 0.4 mm incisogingival width (Fig5). The copings were ultrasonitally cleaned, oxi-dized in a recently calibrated porcelain furnace(Ultra-Mat CDF, Unitek, Monrovia, Calif), then airabraded using 60 >im aluminum oxide followed bysteam cleaning. A review of the literature indicatedthat metal finishing procedures should not have asignificant effect on metal distortion and marginadaptation.'-^'"-'5

Porcelain application was performed on theworking dies that could be placed into the den-toform. Opaque porcelains corresponding to theVita-Lumin shade A-2 were mixed with the mod-eling liquid supplied by the manufacturers, appliedto the castings in two thin layers, and fired as rec-ommended by the manufacturers.

A shoulder porcelain containing a light-poly-merizing resin (Spectrum VLC shoulder porcelain,Dentsply International, York, Pa) was applied to thecastings of group A on working dies thoroughlylubricated with the releasing agent supplied by themanufacturer (Spectrum shoulder porcelain sepa-rator), as recommended by Kessler et al.'" The VLCshoulder porcelain was applied to the shoulder ofthe working die to a height of 2 to 3 mm andcondensed using a porcelain instrument. Theshoulder porcelain was repeatedly blotted using atissue to eliminate any excess light-polymerizingresin. The shoulder porcelain was polymerizedusing a hand-held visible light unit for 20 secondsof exposure. The restoration was carefully lifted offthe working die and any porcelain remaining insidethe casting was removed. The internal gingival sur-face of the porcelain shoulder was then exposedto the visible light unit for 20 seconds. The shoulder

porcelain was reduced to a concave shape usinga white aluminum oxide stone, as recommendedby the manufacturer. The restorations wereallowed to dry for 9 minutes near the porcelainfurnace and were fired according to the manufac-turer's recommendations. A second application ofVLC shoulder porcelain was used to further perfectthe margin prior to the application of dentine andenamel porcelain. The VLC shoulder porcelain wasapplied to the shoulder of the restoration andseated back onto the working die using an ultra-sonic porcelain condenser. The shoulder porcelainwas repeatedly blotted using a tissue to eliminateany excess light-polymerizing resin. The shoulderporcelain was then polymerized as previouslydescribed and fired according to the manufactur-er's recommendations.

Vita shoulder porcelain (Vident, Baldwin Park,Calif) was applied to the castings of group B onworking dies thoroughly lubricated with a releasingagent (Modisol, Vident). The shoulder was con-structed to an incisogingival height of 2 to 3 mmand condensed using vibration. The copings wereallowed to dry in front of a 1,112°H oven for 5minutes. They were transferred to the opening ofthe furnace muffle and fired according to the man-ufacturer's recommendations. A second shoulderapplication was used to further perfect the marginprior to the application of dentine and enamel por-celains. Shoulder porcelain was applied to theshoulder of the restoration, which was then gentlyseated back onto the working die using some vibra-tion. The same firing sequence was followed. Therestorations, including those of the control groupC, were finished to complete contour with twoapplications of dentine and enamel porcelainsusing the adjacent dentoform teeth as a guide.They were then fired and autoglazed according toeach manufacturer's recommendations. The fin-ished restorations were adjusted to fit the masterdies using Micro-Red Equilibrating and IndicatingEmulsion (Culver Laboratories, San Diego, Calif).Vistjal verification under magnification was used toassess the fit and adjustments made using a high-speed handpiece and diamond bur.

The completed crowns were cemented to theirrespective master dies using zinc phosphatecement (Fleck's Cement, Mizzy Inc, Clifton Forge,Va) mixed to the manufacturer's specifications. Anew mix was used for each crown. The crownswere first seated with finger pressure and thenplaced under a 6-kg load for 5 minutes. Followingremoval from the load, they were left undisturbedfor an additional 10 minutes.

A scanning electron microscope (Model 1820,

4, Number 6, 1991 5 1 1 The Inlernationai |ojrnal of Pro.ith odor lies

Portulaln M.irnlns In Mclal Ceramic Rpstoratioris

Fig 6 Diagram of specimen positioned in scanning electronmicroscope for laDial evaluation.

Amray Inc, Bedford, Mass) was used to evaluatetbe marginal adaptation of tbe test specimens. Tbespecimens were luted to a circular aluminunn scan-ning electron microscopy mounting plate withcyanoacrylate using a silicone alignment apparatus.Tbe mounting plate was milled to give a flat surfaceperpendicular to the mounting surface. The spec-

imens in eacb group were assigned random numbers for sequencing measurement to rennove a yselection bias. Tbe specimens were sputte r̂ coatwitb approximately 500 nm of gold-palladium.

The specimens were placed on the stage ot tnescanning electron microscope and aligned by plac-ing the edge of tbe milled surface parallel to theelectron beam at 25X magnification (Fig 6). Thereference mark was then located and centered intbe monitor. Scanning electron photomicrographswere nnade of an approximate 1-mm mesiodistalwidtb of the midfacial and midlingual margins at aworking distance of 12 mm with a magnificationof 100X (Figs 7 to 12).

Tbe photomicrographs were reflexively digitizedby an experienced operator ijsing tbe HatnamatsuC2400 Newvicon tube video camera. The toothcavosurface margins and tbe restoration marginsacross the photomicrograph were traced (TRACEProgram, Image Analysis Facility, University ofIowa, Iowa City]. The TRACE data files were thenread by the DIANAL (Diameter Analysis) Program(Image Analysis Facility. University of Iowa, IowaCityj using 512 X 512 pixels within tbe 1-mm area.Eacb pixel bad 8 bits of intensity information or256 possible gray levels. Image processing andanalysis techniques were accomplished using theMicroVAX II minicomputer (Digital EquipmentCorp, Maynard, Mass) running Lips software(Gould Inc, Image and Grapbics Div, Fremont,Calif) and using tbe DVP Model 18500 Image Pro-cessing System (Gould Inc, Image and GraphicsDiv). Measurements obtained included tbe mean,maximum, and minimum marginal discrepancieswitbin tbe 1-mm area of tbe photomicrograph.

Results

The mean marginal discrepancies and standarddeviations are categorized in Table 2. An analysis"of variance (ANOVA), at a confidence level of .95(alpba = .05), was used to interpret tbe data

Table 2 Mean Marginal Discrepancies and Standard Deviations

GroupStandarddeviation

Minimumvalue

Maximumvalue

A

B

C

LabialLingualLabialLingual

LabialLingual

10101010

1010

eB.3440.34

66.1546.96

45.8649.83

33.0415.9620.28

8.61

13.7613.93

21.9523.31

42.5739.24

26.4433.10

148.3566.49

97.7464.76

69.1074.56

The inlernalionai Journal of Prosthodonlic 512 I 4, Numbe

Porcelain Margins m Melal Cecömic Resloralions

Fig 7 Representative scanning electron micrograpfi of metalcollar metal ceramic restoration (labial view).

Fig 8 Representative scanning electron micrograph ot metalcollar metal ceramic restoration (lingual view).

Fig 9 Representative scanning electron micrograpti of Vitastioulder porcelain metal ceramic restoration (labial view).

Fig 10 Representative scanning electron micrograph ot Vitastioulder porcelain metal ceramic restoration (Iinguai view).

Fig 11 Representative scanning electron micrograph cfSpectrum VLC stiouider porcelain metal ceramic restoration(labial view).

Fig 12 Representative scanning electron micrograph ofSpectrum VLC shouider porceiain metal ceramic restoration(lingual view).

4, Number 6, 1991 The International Journal of Prosthodontics

Table 3 Analysis of Variance. Dependent Variable: Labial Marginal DiscrepancySum ofsquares

Meansquare

BootMSE

Labialmean

ModelErrorCorrected totaiGroup

9030.9115228.4924259.40

9030.91

4515.45564-02

35.21

67.45 23.75

Table 4 Analysis of Variance. Dependent Variable: Lingual Marginal Discrepancy

Sum ofsquares

Meansquare

RootMSE

Lingualmean

MOOBIErrorCorrected total

22729

551.064739 215290.27

275.53175.53

Group

13.25

Table 5 Ryan-Einot-Gabriel-Welsch Multiple RangeTest: Labial Marginal Discrepancy

Table 6 Ryan-Einot-Gabriel-Welsch Multiple RangeTest: Lingual Marginal Discrepancy

Group N

A 10B 10C 10

Alptia = .05, df = 27,

Number of means

Critical range

Mean ¡um)

45.8668.1588.34

MSE = 564.018

2

21.79

REGWO grouping-

ABB

3

26.33

Group

ABC

N

101010

Alptia = .05, df =

Number of means

Criticai range

Mean (^m]

40.3448 9649.83

27, MSE = 175.526

2

12.16

REGWQ grouping-

AAA

3

14.69

•Maans with same REGWQ grouping are not stat:slically difierent. •Means wilh same REGWQ grouping are not statisticaliy different.

(Tables 3 and 4). The Ryan-Einot-Gabriel-WelschMultiple Range Test was used to determine signif-icant differences between tbe groups (Tables 5 and6).

Measurements made from digitized scanningelectron micrographs indicated that group C (therestorations fabricated with a labial metal collar)exhibited the least marginal discrepancy, with amean marginal opening of 45.86 ± 13.76 ^m. Thiswas followed by group B (the restorations with alabial shouider fabricated using Vita shoulder por-celain), with a mean marginal discrepancy of 68.7 5± 20.28 ^m, and group A (the restorations with alabial shoulder fabricated using Spectrum shoulderporcelain), witb a mean marginal discrepancy of88.34 ± 33.04 fim.

The ANOVA indicated significant differencesbetween the labial margins (P < .05). The Ryan-Einot-Cabriel-Welsch Multiple Range Test dem-

onstrated that the mean labial marginal discrep-ancies of group C were significantly less than thoseof groups A and B. The mean labial marginal dis-crepancies of group A and Croup B were not sta-tistically different.

No significant differences were found betweenthe lingual marginal discrepancies (P < .05) of therestorations of the three groups.

Discussion

The mean marginal measurements of the all por-celain margins obtained in this study are within therange of marginal discrepancies previouslyreported.'.^.^i.^^ The marginal discrepanciesreported in this study, however, are greater thanthose reported in the adaptation studies of VVan-serski et al^ and Omar." This may be the result ofthe restorations of this investigation being niea-

The Internationa 5 1 4 Volume 4, Number f.

elam Margini in Melal Ceri

sured following cementation. Eames et aP-" hasreported that castings are usually elevated an addi-tional 20 um or more after cementation.

Hunt et al^" also attempted to investigate theeffect of cementation. The results of their studyalso showed an increase in marginal opening fol-lowing cementation, but the mean marginal dis-crepancies were less than those observed in thepresent study. Only a limited number of specimenswere measured in that study and no statisticalanalysis was performed.

Belser et al,' in an in vivo study, observed thechange in marginal discrepancy before and afterluting with zinc phosphate cement. Their resultsshowed an increase in marginal discrepancy thatwas not significant. The marginal discrepanciesmeasured for the all-porcelain margins weresnnaller than those observed in this investigation.This may be the result of using the platinum foiltechnique for fabrication of the labial porcelainmargin, which has been shown to produce smallermarginal discrepancies than the direct lift tech-nique used in this study.^

Another factor that may have influenced theresults of this investigation is the technique sen-sitivity of the fabrication of the all-porcelain margin,Wanserski et al' and Omar* used two correctionapplications of shoulder porcelain to fabricate theall-porcelain margins. In the present study, thetechnique manuals provided by each manufacturerwere followed as closely as possible to maintainclinical applicability. The Spectrum VLC systemtechnique manual does not specifically recom-mend any correction applications to further perfectthe nnargin. During a pilot study, it was found thatone application did not give visually acceptablemarginal adaptation. The Vita shoulder porcelaintechnique manual recommends correction appli-cations, including one application after the resto-ration is finished to complete contour. In anattempt to make the two systems more compara-ble, one correction application was used for eachsystem. An additional correction application fol-lowing finishing of the restoration to complete con-tour was not attempted because the viscosity ofthe Spectrunn VLC porcelain system made handlingthe material difficult. If an additional application ofthe Vita shoulder porcelain had been used, themean marginal discrepancies of the Vita group mayhave approached those of the conventional metalcollar group while creating a larger difference fromtbe marginal discrepancies of the Spectrum VLCshoulder group.

The mean marginal discrepancies measured inthis investigation are well within the reported clin-

ically acceptable range for a gingival margin. Chris-tensen's linear regression formula showed that thelargest acceptable opening of tbe occlusal marginof a gold inlay was 39 ßvn, while that of the gingivalmargin was 119 ; /m." McLean and von Fraunho-fer,-" in an in vivo study, also showed that a mar-ginal opening of less than 120 (im was clinicallyacceptable. The largest mean marginal discrepancymeasured in the present investigation was that ofthe Spectrum VLC shoulder porcelain group, withan opening of 88.43 ± 33.04 >im.

The use of lighl-pulymerized resin as the shoul-der porcelain binder did not improve the ease offabrication of the all-porcelain labial margin. Oncethe material was applied to the restoration andpolymerized, the restoration was difficult toremove from the stone die without damaging thedie. The polymerized margin appeared to be welladapted, but considerable shrinkage appeared tooccur during firing.

An opaque layer with a matte finish was foundto be critical for obtaining a bond between theopaque porcelain and the shoulder porcelain.Without this matte finish, the shoulder porcelainhad a tendency to chip off the restoration at themetal/porcelain ¡unction in the interproximalareas. It was also critical to allow time for the light-polymerized resin to evaporate from the porcelainprior to placing the restoration into the porcelainfurnace.

The midfacial measurement location wasselected as a result of previous adaptation studieswhich have shown that the midfacial location ofthe all-porcelain margin exhibits the greatestchange in marginal adaptation during fabrication.^The midlingual measurement location was selectedto demonstrate the ultimate fit of the metal coping.An area approximately 1 mm in size was selectedfor measurement, rather than a single point, toobtain a range of measurements over the area.

The imaging techniques used have not been pre-viously reported. The use of the scanning electronmicroscope for the evaluation of marginal discrep-ancy has been reported.'•=" These studies usedepoxy resin replicas produced from elastomericimpression materials. In the present study, place-ment and alignment reproducibility of the speci-mens was evaluated by placing one specimen intothe cbamber of the microscope and aligning it fourseparate times. The resulting micrographs weredigitized and traced as previously described. Thestandard error of measurement calculated was 0.83itm (P < .OS), while the standard deviationbetween the four micrographs was 1.65 ¡im. Thisindicated that the reproducibility of placement and

- 4, Number 6, 1991 5 1 5 The International lournai of Proslfiodonlics

alignment of the specimens, as well as the abilityof the investigator to consistently trace the margins,was reliable.

Coticlusions

Under the conditions of this study, the followingconrlusions can be made:1. The mean marginal discrepancies of the all-

porcelain [abial margin metal ceramic resto-rations fabricated using Vita shoulder porce-lain and Spectrum VLC shoulder porcelainwere not significantly different.

2. The mean marginal discrepancies of the all-porcelain labial margin metal ceramic resto-rations fabricated using either Vita shoulderporcelain or Spectrum VLC shoulder porcelainwere significantly larger than those of con-ventional metal margin metal ceramic resto-rations.

3. There was no statistical difference betweenthe mean marginal discrepancies of the lingualmargin for the three groups.

4. The mean marginal discrepancies of the metalceramic restorations measured were withinthe range generally acknowledged to be clin-ically acceptable.

Acknowledgments

The authors express sincere appreciation to Dr lames ivl.S.Clancy for editorial assistance; to Mr |ohn l.affoon for his S£Mtechnical support; to Mr Boyd Knosp and Mr Steve Beck fortheir Image Analysis support; to Mrs lane lakobsen and DrWilliam lohnston for their statistical support; and to DentsplyInternational, Vident Corp, and lelenko Dental Health Prod-ucts for the generous use of their materials.

References

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2. Cooney IP, Richter WA, MacEntee Ml: Evaluation ofceramic margins for metal-ceramic restorations. / ProsthetDeni 1985:54:1-5.

3. Wanserski DJ, Sobczak KP, Monaro |G, McCrvney GP: Ananalysis of margin adaptation of ail-porcelain facial marginceramometal crowns, / Prosthet Dent 19B6;56:289-292.

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Faucher RR, Nicholls|l: Distortion related to margin designin porcelam-fused-to-metal restorations. / Frosthet Dent1980;42:149-155.Hamaguchi hi, Cacciatore A, Tueller VM: Marginal dis-tortion of the porcelain-bonded-to-metal completecrown: An SEM study.; Prasf/iei Denn9B2;47:146-l 53.Richter-Snapp K, Aquilino SA, Svare CW, Tumer KA:Change in marginal fit as related to margin design, alloytype, and porcelain proxirnity in porcelain-fused-to-metalrestorations. / Prosthet Deni 1987;6Ü:435-439.Shillingburg HT, Hobo S, Fisher DW: Preparation designand marginal distortion in porcelain-fused-to-metal res-torations. / Prosthet Dent 1973;29:276-2e4.Kessler |C, Brooks TD, Keenan MP: The direct lift-off tech-nique for constructing porcelain margins. Quint Dent/ec/jno/l988;l0:145-l50.

Schneider DM, Levi MS, Mori DF: Porcelain shoulderadaptation using direct refractory dies / Prosthet Dent1976;36:583-587.StratingH, PameijerCH, Gildenhuys RR: Evaluation of themarginal integrity of ceramometal restorations. Part 1. /Prosthet Dent 1981;46.59-65.Eames WB, O'Neil S|, Monteiro J, Miller C, Roan |D |r,Cohen KS: Techniques to improve the seating ol' castings.I Am DeiiM5soc1978;96:432-437,Hunt JL, Cruickshanks-Boyd DW, Davis EH: The marginalcharacteristics of collarless bonded porcelain crowns.Quint Dent Technoi ^97S;2(9)•.2^-2b.Christensen GJ: Marginal fit of gold inlay castings. /Prosthet Dent I966;16:297-305.McLean |W, von Fraunhofer |A: The estimation of cementhim thickness by an in vivo technique. Br Dent Il 97 l ;13 l : ]07 - in .

1 of Pjosihodontii 516 Volume 4, Number 6, 199]