influence ofthe restorative technique and new adhesives on the
TRANSCRIPT
operative Dentistry
Influence ofthe restorative technique and new adhesives on the dentinmarginal seal and adaptation of resin composite Class II restorations:An in vitro evaluation
D. Dietschi*/G. De Siebenthal**/L. Neveu-Rosenstand**/J. Holz***
The aim ofthe present in vitro study was to evaluate the marginal adaptation and seal of directand indirect (inlay) Class H resin composite restorations made with Z¡00/Scotchbond MP orHerculite/Optibond. Tlie quality of margins in dentin was assessed for restorations made withor without a hning of glass-ionomer cement or resin-modified glass-ionomer material. Therestored teeth were submitted to thermocycUng and then to replication for scanning electronmicroscopic obser\-ation and to a dye infiltration test, ¡n the present test conditions, theinlay technique proved its superiority over t¡ie direct re.storative method. The quality ofthedentinal margin of restorations made with Z ¡00/Scotchbond MP appeared also slightlybetter. Both the glass-ionomer cement and the resin-modified glass-ionomer material, whenapplied as a lining, increased leakage and downgraded marginal adaptation. The fullbonding with modern adhesives appeared to be the most efficient way to enhance the marginalquality of both direct and Indirect restorations. (Quintessence Int ¡995;26:717-727.)
Introduction
Resin composites were used as early as 1966 (Addent12, 3M Dental) for the restoration of posterior teeth.However, the clin]ca] performance ofthe early formu-lations was disappointing,'- justifying the effortsexerted to develop better-performing restorative sys-tems. The high incidence of posterior resin compositefailures was often related to improper preparation andrestoratiye techniques,^-^ in addition to insufficientphysicomechanical properties and wear resistance ofresin composites.'"'
Besides the continual material improvements, moresophisticated and multilayering insertion techniques
" Lecturer, Departmenl of Prevenlivc and Restorative Denlistry,University of Geneva, School of Dentistry, Geneva, Switzerland.
** Research and Teaching Assistant, Department of Preventive andRestorative Dentistry, University of Geneva, School of Dentistry,Geneva, Switzerland
*** Professor and Director, Department of Preventive and RestorativeDentistry, University of Geneva, School of Dentistry, Geneva,Switzerland,
Reprint requests; Dr D. Dietschi, Lecturer, Department of Preventiveand Restorative Dentistry, University of Geneva, School of Dentistry,19, rue Barthélémy-Menn, 1205 Geneva, Switzerland.
were developed for posterior teeth to overcome thedestructive influence of resin composite polyme-rization shrinkage and to achieve better marginaladaptation and sea!.•*•*""* DifFerent resin compositeinlay systems"'- were also developed with someadvantage regarding the margina] quality in the criticalpróxima] areas. Certain characteristics ofthe residualenamel and preparation design proved to significantlyinfluence the adaptation and seal ofthe restoration.'^Marginal quality of posterior adhesive restorations inenamel may therefore be optimized by selecting theappropriate restorative technique.
In Class V restorations, the use of better-perfomiingadhesives together with speciai restorative procedureshas been proposed to improve the quality of thedentinal margin and has proved to perform satisfac-torily, at least in vitro.'''"'^ However, only a few recentstudies have demonstrated that equivalent success canbe achieved in the adaptation and seal of dentinalmargins in Ciass II restorations."'"
The influence of base materials'*'^ and restorationconfigtiration-'̂ "^^ have also proved to be of primaryconcern for marginal quality.
Quintessence Internationai Volume 26, Number 10/1995 717
Operative Dentistry
Fig 1 Standardized cavity
The aim of this in vitro study was therefore toevaiuate the quality of dentina[ margins in Ciass IIadhesive restorations made with two modem resincomposites and adhesive systems. The influence ofionomer-based hnings, as weil as of the restorativetechnique, on marginal seal and adaptation was alsoevaluated.
Method and materials
Specimen preparation
Freshly extracted intact human molars with a completeapexiflcation were used for this study. To preventdehydration ofthe pulpal tissue, the root tip of eachtooth was cut immediately after extraction. The teethwere then stored in saline at 4°C until the experimentwas initiated.
Two standardized occlusoproximal cavities wereprepared on both proximal sides, extending I.O mmunder the cementoenamel junction (Fig 1). Slightlytapered preparations were made for both the directtechnique and the indirect technique; the cavity basewas 4.0 mm in width and 1.5 mm in depth. All marginswere flnished gingivally with a butt preparation.
Two resin composite materials with their respectivedentinal bonding agent were tested in this study-asmall-particle hybrid material (Herculite XRV [ HERC]
with Optibond, Kerr/Sybron) and a monomodalspheroidal material (ZIOO with Scotchbond Multi-purpose IMP], 3M Dental), Each of these resincomposites was used with two different restorativetechniques (a direct multilayer technique and an inlaytechnique). For each of the four resulting combi-nations, three different proximal conflgurations wereadditional[y evaluated: without basehning or with ahning ofthe pulpal axial wal[ with a traditional glass-ionomer cement (Ketac-Bond Applicap, ESPE) oraresin-modified glass-ionomer material CVitrebond,3M Dental).
For the Ketac-Bond lining only, dentinal walls wereactively conditioned for 30 seconds with a small brushdampended in 3% sodium hypochlorite solution. Bothcements were apphed in strict accordance with themanufacturer's instructions. Vitrebond was light curedfor 30 seconds (Elipar light curing unit, ESPE). Afterthe cement had set, excess was removed to obtain aregular thickness ofthe lining, providing gingivally a1,0-mm free border. The linings were neither inten-tionally etched nor primed, prior to or during the nextprocedures.
An eqtial number of cavities (n - 10) was restored ineach of the 12 experimental restoration groups,summarized in Table 1.
Restorative techniques
Direct multilayer technique
For groups 1 to 3 (Scotchbond Multipurpose Adhe-sive), enamel and dentin were etched together for 15seconds with a 10% maleic acid semigel. The cavity wasthen thoroughly rinsed witb water for 15 secondswithout pressure and gently air dried. The primingsolution was then applied on the dentin and gentlydried. Thereafter, all the cavity surfaces were coveredwith the liquid resin, which was light cured for 40seconds.
For groups 7 to 9 (Optibond Adhesive), enamelwas selectively etched with 37% phosphoric acid gelfor 30 seconds, whereas dentin was exposed to thephosphoric acid for only 15 seconds. Rinsing and airdrying ofthe cavities followed as already described. Allthe dentina! surfaces were first covered with theprimer, dried, and polymerized for 20 seconds. Thedual-cured adhesive was then applied to all of thecavity surfaces and light cured for 40 seconds.
The next steps were similar for all direct restorationgroups. A staittless steel matrix was adapted to theprepared tooth before the incremental insertion oftherestorative material. Several 1,0-mm resin composite
718 Quintessence International Volume 26. Number 10/1995
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Table 1 Distribution ofthe experimental variables among the different groups
Material Bonding agent Technique Lining
123
456
789
101112
ZIOOZIOOZIOO
ZIOOZIOOZIOO
Herculite XRVHerculite XRVHerculite XRV
Herculite XRVHerculite XRVHerculite XRV
Scotchbond multipurposeScotchbond multipurposeScotchbond multipurpose
Scotchbond multipurposeScotchbond multipurposeScotchbond multipurpose
OptibondOptibondOptibond
OptibondOptibondOptibond
DirectDirectDirect
InlayInlayInlay
DirectDirectDirect
InlayInlayInlay
NoneKetac-BondVitrebond
NoneKetac-BondVitrebond
NoneKetac-BondVitrebond
NoneKetac-BondVitrebond
layers were placed, starting at the bottom ofthe cavity,and each was polymerized 40 seconds from theocclusal direction. After removal of the matrix, allrestoration suriaces were covered with a glycerine gel(Airbiock Gel, DeTrey/DentspIy), which was poly-merized for 60 seconds from the gingival and occlusaldirections.
Inlay technique
After completion ofthe preparation, the cavities wereinsulated by means ofa thin iayer of glycerine gel. Aftera transiucent matrix had been placed, tbe resin com-posite was inserted into the cavities in one incremetitand hght cured for 60 seconds from the gingival andocclusal directions.
The inlays were then removed from the tooth andtheir internal surface was polymerized for 60 addi-tional seconds. The inlays were reseated, and, in casesof excessive friction, their internal surface was slightlyreduced (mainly on pulpoaxial walls) until an optimaland free placement could be obtained. The inlays weresubjected to a photothermal treatment (at 110°C ) for 7minutes in a special oven (D,I 500 oven, Coltene).
The prepared teeth were conditioned following thesame procedures appiied to the direct restorations.After impregnation of the tissues with the primer, athin iayer ofthe hquid resin was subsequently appliedand left uncured. The inner surfaces ofthe inlays wereroughened with a coarse grain diamond and alsocovered with the resin, prior to the cementation.
Dual-cured resin composite cements, similar incomposition to the re sin-composite restorative mater-ial, were used (Luting Material Cement, 3M Dental,for groups 4 to 6 and Porcelite Dual Cure, Kerr/Sybron, for groups 10 to 12). The catalyst and basepastes of the cement were mixed in a 1:1 ratio andapplied on all internal surtaces ofthe cavity. The inlaywas then seated with a progressive force appliedocciusally; excess cement was continuously removedwith a probe. After the final inlay seating, a smailbrush, slightiy dampened in the liquid resin, was usedto level the margins. The resin-composite luting ma-terial was finally light cured for 60 seconds from thegingivai and occlusal directions after having beentotally covered by the glycerine gel.
Finishing and thcnnocycling
Finishing and polishing of proximal surfaces wereperformed similarly for both direct and indirectrestorative techniques using flexible disks (Pop-on,3M Dental).
The specimens were then stored for 24 hours insaline at 37°C before being subjected to 5,000 com-piete thermal cycles of I-minute water baths at 5°Cand 55°C,
Evaluation of marginai adaptation
Epoxy resin replicas of the restored teeth werefabricated from poly(vinylsiloxane) impressions. Thereplicas were gold plated for observation in the
Quintessence International Volume 26, Number 10/1995 719
operative Dentistry
Fig 2 Different sections and theirposition in the specimen.
Fig 3 Scaie used for evaluating the dye infiltratiori.
scanning electron microscope (SEM) (Phillips XL20). The adaptation between the restorative or lutingresin composite and dentai tissues of the axiai andgingival mai^ins was evaluated semiquantitively forthe following parameters, adapted from Ltiescher etal,' Lutz and Kuli/ and Roulet-"": continuity (C).polished overfilling (POF), overfilling (OF), underfil-ling (UF). marginal opening (MO), marginal restora-
tion fracture (MRF), marginal tooth fracture (MTF),and satisfactory adaptation (SA), equivalent to thesum of continuity, poiished overfilling, overfilling, andunderfilling.
The replicas were observed at a standard x 300magnification under a tilt of 15 degrees and anaccelerating voltage varyitig between 10 and 15 kVResults were expressed as percentages of the totalproximal limit length for every parameter.
Evaluation of marginal seal
Specimens were immersed in a 0.5% cresyl bluesolution for 24 hours after the roots were protectedwith a nail vamish up to 1.0 mm from the restorationlimhs. After completion of this procedure, the speci-mens were thoroughly rinsed and dried.
The teeth were embedded in a self-curing epoxyresin and sectioned in three parts with a slow-rotatingsaw (Isomet 11-1 ISO, Buebler) (Fig 2). The thicknessofthe centrai slice was 800 |im.
The penetration of cresyl blue dye was evaluatedunder a binocular microscope (STEMI SVl 1, Zeiss) atX 30 magnification. Observations ofthe dye penetra-tion (DP) were made on the three sections. Infiltrationscores represented the extent of dye penetration alongthe gingivopulpal adhesive interface as a percentage ofits total icngth, 100% representing intlltration to thetop ofthe pulpal wall (Fig 3). Results were expressedas a mean per specimen, calculated from the fourobservable surfaces. The presence or absence of dyeinside tbe dentin was also recorded.
720 Quintessence International Volume 26, Number IO/1995
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Table 2 Extent of dye peneiration along the proximaladhesive interface (% of length of interface}
Group
Z i 00-1ZiOO-I-VHERC-1ZIOO-D-VHERC-I-KZiOO-l-lCZiOO-DHERC-DHERC-1-VHERC-D-VHERC-D-KZIOO-D-K
Mean (± SD)
2.40 ( 2.22)9.02 (17.23)
24.25 (17.59)33,75 (19,53)34.75(20.24)36.83 (27.60)37.00(13.52}60.35 (26.30}63,22(13.28)67.15 (23.25)68,75 (36.04)75.96 (22,96)
1 = Inlay; V = Vitrebond: D = direct: K = Keiac-Bond.Groups connected by a vertical line are not statisticallydifferent from each other i,P< .05).
Statistical anaiysis
The influence of the three experimental variables(restorative material, restoration technique, and base-iining) and their possibie interactions were explored ina three-factor analysis of variance ( ANOVA). Statisti-cally significant differences in marginal adaptation ormarginal seal scores between the experimental groupswere investigated by a one-factor ANOVA and Scheffe'stest.
Results
Marginal seal
The mean scores and standard deviations ofthe cresylblue infiltration test are presented in Tabie 2, togetherwith the significant differences and percentage ofspecimens exhibiting dentinal dye penetration. Resultsofthe evaiuation of marginal seal are summarized inFigs 4a to 4f.
The three variables demonstrated a significantinfluence on gingival marginal seal of direct andindirect Class II resin composite in dentin. Thethree-factor ANOVA also revealed an interactionbetween materials and baseiining. The inlay restor-ations exhibited less marginal leakage than did directrestorations in tiie same configuration (DP for inlays:2.4?¿ to 57,92%: DP for direct restorations: 33.75% to
75.96%}. The association of ZIOO and ScotchbondMP exhibited generally less leakage than did HERCwith Optibond in similar configurations (DP forZIOO: 2.4% to 36.83%; DP for HERC: 24.25% to67.15%), except for the direct restoration with Ketac-Bond baselining (DP for ZIOO; 75.96%; DP forHERC: 68.75'Ü}. Except for ZIOO inlays with orwithout Vitrebond lining, specimens predominantlyexhibited dye penetration in dentin.
Marginal adaptation
The mean percentages of gingival and axial marginaiadaptation arc presented in Tables 3 to 5. Results ofthe evaluation of marginai adaptation are summarizedin Eigs 5a to 5f for gingival margins and in Figs 6aand 6b for axial margins.
The axial margins showed very few marginal defects(percentages of satisfactory adaptation varying from70% to 100%). Only direct HERC restorations with aVitrebond lining showed a higher percentage of axialmarginal opening ( 39,15% ) than the other groups (0%to 20.53%). Most axiai adaptation defects wereobserved under the cementoenamel junction.
Each variable proved to infiuence the marginaiadaptation of gingival margins. The three-factorANOVA also revealed significant interactions amongmaterials and baselinings, techniques and basclinings,materials and techniques, as well as among all threevariables together. Considering each specific experi-mental configuration, the gingival adaptation of inlays(SA: 56.47% to 95.37%} proved generally to be ofbetter quality than that of direct restorations (SA:24.48% to 95.37%). The presence of Vitrebond aslining negatively influenced the gingival adaptation ofHERC iniays (SA: 56.47%) as well as ofthe ZIOOdirect restoration (SA: 40.97%) when compared to thesame configurations without lining (SA for HERCinlay; 86. Í2%; SA for 2100 direct restoration: 95.37%)or with the Ketac-Bond baselining (SA for HERCinlays: 81.73%: SA for ZIOO direct restorations;90.24%). Direct HERC restorations demonstrated thelowest rate of satisfactory adaptation (24.48%).
The association of ZIOO and Scotchbond MP alsoshowed a slight superiority to the HERC and Opti-bond combination in marginal adaptation (SA forZIOO; 40.97% to 95,37%; SA for HERC; 24.48% to86.12%}.
In gingiva! margins, the predominant defect record-ed was the marginal opening (2.96% to 74,98%).
Percentages of marginal tooth fracture and marginalrestoration fracture were present in axial enamei
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Figs 4a to 41 Evaluation ot marginal seal: results of the dye infiltration test.
NONE KETAC VITREBOND
Base-lining
Fig 4a Mean percentages ot dye intiltration scores alongthe adhesive interface for direct restorations
Fig 4c Section ot a Z1Ü0 direct restoration without alining. Leakage could not be totally prevented when thedirect technique was used. (Original magnitication x 40.)
Fig 4e Section of a HERC direct restoration with aKetac-Bond lining Extensive leakage is evident (Originalmagnification x 22.)
1DD
S SO
S1 '"5 40
I "
//
\^ y^
1
DZ100• HERC
NONE KETAC VITREBOND
Base-lining
Fig 4b Mean percentages of dye intiltration scores alongthe adhesive interface for inlays
Fig 4d Sectior ot a Z100 inlay witfiout a lining. No leakageis visible. (Original magnification x 50 ¡
Fig 4f Section of a HERC inlay with a Ketac-Bond liningSome leakage is present, but the dye penetration is lessthan Ihaf which occurred in the direct resloration, (Originalmagnitication x 22.)
722 Quintessence International Voiume 26, Number 10/1995
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Table 3 Gingival marginal adaptation {% ofsatisfactory adaptation)
Table 4 Gingival marginal adaptationmarginal opening)
of
Group
HERC-DHERC-D-VZIOO-D-VHERC-I-VHERC-D-KZIOO-I-KHERC-I-KHERC-IZIOO-D-KZIOO-DZIOO-IZIOO-I-V
Mean (+ SD) Group
24.48(26.07) ZIOO-132.26(30,85)40.97 (26.94)56.47(27.18)
ZlOO-I-V
69.99(23,36)80.11 (30.48)81,73 (18.59)
ZlOO-D
86.12 (13.81)90.24(13.85)95.37 ( 7.50)95.37 ( 7.50)95.37(10.24)
HERC-lZlOO-D-KHERC-D-KZlOO-I-KHERC-I-KZlOO-D-VHERC-I-VHERC-D-VHERC-D
Mean (± SD)
2.96 ( 4.80)2.96 ( 6.55)3.04 ( 6.93)6.14 ( 6,13)6.24 ( 8.85)6.87(15.72)9.52(15.04)
18.23(18.57)37,76(17.24)41,72(24.68)67,61 (30.85)74,98(25.61)
D = Direct; V = Vitrebond; 1 = inlay; K = Ketac-Bond,Groups connected by a vertical line are not statisticallydifferent from each other (.P< ,05),
I - Inlay; V = Viirebond; D - direct; K = Ketac-Bond,Groups connected by a vertical line are not statisticallydifferent from each other (P< .05),
margins only with insignificant scores and differences(MTF: 0% to 6.61%; MRF: 0% to 7,39%).
Discussion
For direct restorations, the widely used conventionalmultilayering technique with horizontal incrementswas applied, assuming that other existing but moresophisticated and complicated methods are not clin-ically appropriate where the interproximal preparationextends in dentin, reducing accessibility.
An SEM observation of restoration replicas and aclassic dye inflltration test were applied in thisexperiment. The combination of the two methodsmade possible the observation of both the superflcialdefects in marginal adaptation and the extent of defectsinside the adhesive interface, respectively With fewexceptions, the results yielded by the tests of marginaladaptation and seal proved to be in good accordance.
Marginal seatNone of the configurations was able to provide aperfect marginal seal on dentin. However, comparedwith other conflgurations, Z100 inlays with or withouta Vitrebond lining showed ver>' little leakage.
For both resin composites, the lowest inflltrationscore was obtained with the inlay technique without
Table 5 Axial marginal adaptation (% ofsatisfactory adaptation)
Group
HERC-D-VZIOO-D-VHERC-I-KZIOO-I-KZlOO-D-KHERC-I-VHERC-D-KHERC-IZlOO-I-VHERC-DZIOO-DZlOO-I
Mean (± SD)
55.96(27.47)69.90(17.57)76.81 (24.17)79.91 (20.20)86.26(13.17)86,87 ( 7,45)89,54(20,28)89,81 (15,40)90,04(10,12)90,10(10,03)
100,00 ( 0,00)100,00 ( 0,00)
D = Direct; V = Vitrebond; 1 = inlay; K = Ketac-Bond.Groups connected by a vertical line are not statisticallydifferent from each other (/•< ,05).
lining. This conflguration appeared the ideal one toachieve optimal seal on dentin, assuming that directbonding to dentin with new adhesives is more efficientthan indirect bonding through glass-ionomer or resin-modified giass-ionomer linings. In vitro data con-
Quintessec rnitinml iM'imgSfi Niimh-"- 10/1995 723
Operative Dentistry
Fig 5a to 5f Gingival marginal adaptation in denlin: resulls of the SEM observation.
100
o.
™ 60
g 20
/y-
\
• HERCDZlOO
NONE KETAC VITREBOND
Base-lining
Fig 5a Mean percentages of satistactory adaptation fordirect restorations.
MOME KËTAC VITREBOMD
Base-lining
Fig 5b Mean percentages of safisfactory adaptation forinlays.
Fig 5c ZIOO direct restorations without a lining The Fig5d ZIOO inlay with a Vitrebond lining. The restoralion ismargin is in continuity. (Original magnification x 300). in perfect continuify with dentin, (Original magnification
X 300),
Fig 5e HERC direcf restoration without a lining Ttiemarginal opening is clearly visible. (Original magnificationX 300),
Fig 5t HERC inlay The margins are in continuity (Originalmagnification x 300).
724 Quintessence Intemational Volume 26, Number 10/1995
Operative Dentistry
Fig 6a and 6b
1•a
3
ï
100
so
60
ic 1
D
Axial marginai adaptation
1 1 1 1 1( O-K I-K D-V I.V
Base-lining
in snamei' re
11J
• HËRCDZ1Q0
sul
7
Fig 6a Mean percentages of satisfactory adaptation fordirect restorations and inlays. Direct ¡D], iniay (i); direct witfiKetac-Bond lining (D-K). iniay with Ketac-Bond lining (i-K);direct with Vitrebond lining (D-V); inlay witii Vitrebond lining(I-V).
Fig 6b Z100 direct restoration. Adaptation of axiai mar-gins is setislactory, (Originai magnification x 300).
ceming dentinal adhesion of these different materialssupport this finding.-^"-' Apart from localized pulpalprotection or the restoration of undercuts to preservesound tissues, the need for basellnings under bondedinlays appears doubtM.
In addidon to the limit level (above or below thecementoenamel junction), the cavity dimensions, andrelated volume of resin composite to be cured must betaken into consideration for direct restorations unlikeinlays, where the cavity design has less influence onrestoration seal.'-' It has been shown that a glass-ionomer base can improve marginal quality of Class IIdirect resin composite restorations by reducing thevolume of resin composite and thereby polymerizationshrinkage in proximal areas.̂ * The present resultsfailed to confirm this finding.
This apparently conflicting observation may haveresulted from the minimal volume ofthe cement on thepulpal wall, the cement having been applied as a liningrather than as a base. Actually, the amount of cementthat can be applied in the interproximal areas isrestricted for anatomic reasons. It may therefore beassumed that the relative benefit of reduction involume of resin composite and increase in "freesurface,"-^ presumably obtained with traditional glass-ionomer cements, was counteracted by the reducedsurface available for dentinal bonding at the criticaldentin gingival margin. Here again, the efficiency ofmodem adhesives makes the use of baseiinings contro-versial. Moreover, the recognized benefit of fluoriderelease by glass-ionomer baselincrs-"'^' may also be
discussed now that bonding agents and resin composi-tes containing and releasing fluoride are being develop-
Marginal adaptationA new criterion, satisfactory adaptation, was createdfor evaluating the percentage of margins with a"clinically" acceptable quality. It consists of adding theexisting percentages of poiished overfilling, overfilling,and underfillhig, to the percentage of condnuity. It wasassumed that the latter defects are unavoidable innormal or simulated clinical conditions^"* and presum-ably do not expose the restored tooth to a high risk offurther caries.
Results of the SFM evaluation showed overall thesame diiferences and tendencies as the dye infiltrationtests. Only for direct restorations of HFRC withKetac-Bond, ZIOO with Vitrebond, and ZIOO withKetac-Bond were marginal seal and adaptation scoresnot in good correiation. The least satisfactory marginaladaptation was observed in direct restorations withVitrebond for Z-100 restorations and in direct restora-tions without lining for HERC.
The poor performance of direct ZIOO restorationswith Vitrebond was relatively surprising. Tiie Vitre-bond lining did not generally demonstrate a positiveinfluence on marginal quality for direct restorations orfor HERC inlays. It can be hypothesized that thepotential adbesion of the resin composite to theresinous lining might have restrained the compensa-tory flow at this restorative interface, encouraging
Number 10/1995 725
operative Dentistry
stress accumulation on the gingival dentinal margin.Until dentinai adhesion of these materials has beenconsiderably improved, the application of resinousbaseliners will remain an uncertain procedure.
In the present experimental conditions, ScotchbondMultipurpose demonstrated satisfactory performancewhen used in combination with the 3M resin compos-ite luting cement. Its formulation has been improved,however, because the degree of polymerization ob-tained by the indirect chemical activation through thecomponents of the luting resin composite was ques-tioned. A chemical initiator and catalyst for dentinalimpregnation were included in the new ScotchbondMP Pius adhesive system.
Some inconsistencies in results of evaluations ofmarginai seai and adaptation are often encountered,because scanning eiectron microscopy and dye infil-tration methods have different sensibility thresholds."The occurrence of gaps too small to be observed in theindirect SEM observation, as weil as the possibleexternai localization of some bonding failures, arepresumptive interpretations of such apparent contra-dictions. It is, however, still difficult to ascertain whichofthe two methods is the best predictor ofthe clinicalperformance of tiie restorative systems under evalua-tion. It would seem sensible to consider as potentiallyappropriate for clinical use only those restorativetechniques and materials that performed satisfactorilyin botii evaluation metiiods.
Summary
Marginal seal and adaptation of Class II resin compos-ite direct restorations and inlays was assessed in vitro,using two restorative systems (Scotchbond MP withZIOO and Optibond with Herculite),
Under the present experimental conditions, theresin composite iniay technique proved superior todirect restorations. The association of ZIOO andScotchbond MP presented fewer marginai defects andless leakage tiian did Herculite and Optibond, espe-cially in direct restorations.
Marginai seal and adaptation of inlays did notbenefit from the application of a lining of glass-ionomer cement or resin-modified glass-ionomer ma-terial. Eor direct restorations, the performance of tliosewith ñili bonding appeared equivalent or slightlysuperior to that of restorations with lining. However,traditional glass-ionomer cement seems more appro-priate than resin-modificd glass-ionomer material forbase-lining, because it probably provides a free surfacenecessary for polymerization shrinkage compensation.
Full bonding with new-generation adhesives ap-pears a promising way to enhance restoration quality indentin of both direct and indirect resin composite
restorations.
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David Korson
Aesthetic Designfor Ceramic Restorations
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