The Influence of a Simplified Application Teciinique for Ceramic Iniays on the iVIargin Quaiity

Stefan ClottenVUwe BlunckVJean-François

The adhesive iuting technique for ceramic inlays requires a sequence of muitiple steps that are cumber- some and time consuming. Furthermore, modifications of dentin bonding procedures may negativeiy infiu- ence the margin quality of ceramic inlays with cervicai dentin finishing iines.

Purpose: The objective of this study was to test the effect of a new, simplified procedure for dentin bond- ing on the margin quaiity of ceramic iniays.

Materials and Metiiods: Thirty-two MOD inlay cavities with cervical finishing lines in dentin were prepared into premolars. They were randomly divided into four groups (n = 8); In the balanced design, one parame- ter was the inlay material (Empress/Cerec) and the other the polymerization of the dentin bonding agent, before insertion ofthe inlay (P+) and after insertion of the inlay (P-). Aii inlays were inserted with Varioiink Ii in combination with an enamei and dentin conditioning universal bonding agent (Etch & Prime 3.0). Two parameters were used to determine the inlay quality: (1) the fit, measured by the difference of the inser- tion depth into the cavity between try-in and cementation, and (2) a quantitative margin anaiysis in the SEM at a magnification ot 200!(, performed for the cervical segment before and after thermocycling, using epoxy replicas.

Results: In all four groups the inlays were >5 |im deeper in the cavities than at the try-in session. This is expiained by the substance loss from the etching. The measured difference for Cerec iniays inserted in cavities, where the bonding agent was not polymerized prior to insertion, was significantly larger. Margin anaiysis of the cervicai segment revealed no statistical differences (P < 0.01) tor both criteha tested. The median vaiues for all groups were 100% for oiinical acceptable margin and 0% tor marginal opening. Conciusion; By using the universal bonding agent, high margin quaiities on dentin and enamel are ob- tained with ceramic iniays even with the simplified approach. J Adhesive Dent 1999:1:159-166. Submitted for putjlication: 07.07.98: accepted tor puOication: 17.08.9S

ore and more patients decline the use of amal- is limited to small- or medium-sized cavities that Mgam as a material for the restoration of poste- should be surrounded by enamel,^^ since their mar- rior teeth. As alternatives, composites or inlays are ginal behavior with cervical finishing lines ih dentin recommended.2.3,24-26 The use of direct composites is hot satisfactory.'''5'^'^°'22.27.29 Tooth-colored inlays, however, have demonstrated a superior margin be-

Frankfurter Str. 198 a, D-61118 Bad Vilbel, private practice. The mechanical retention provided by resin tags ' Associate Professor, Dept of Operative Dentistry, Preventive Den- and hybrid layer formation represents the major tistry, and Endodontics, School of Dental Medicine, Humboldt Uni- versity Berlin (Charité), . part ofthe overall bond strength ,3^ but there is little Professor and Chairman, Dept. of Operative Dentistry, Preventive indication for the formation of chemical bonds be- Dentistry, and Endodontics, School of Dental Medicine. Humboldt tween resins and dentih.32-34 Micromechanical re- University Berlin (Charité), Germany. tention is currently accepted as the principal attachment mechanism of adhesive resins to dentin.s."'.i''.i''ii8 jhis includes a cautious etching 1, D-13353 Berlin, Germany pretreatment of the dentin and a diffusion of hy- E-mail: jfroulet® aol. com

159 Vcl 1, Ho 2. 1999 Fig 1 Cavity preparation, (a) Occiusal view. (b) Proximal view.

drophilic monomers into the superficial iayers of MATERIALS AND METHODS the dentin, stabiiized by an ampiphiiic adhesive to create a resin-reinforced dentin iayer, the hybrid Thirty-twc human premolars stored in a 0.5% Chlo- iayer,I'' and the resin tags. These formations have ramin-D-hydarat solution were mounted into stain- to be light cured to withstand the forces during the less steel nuts with resin (Technovit 4004, Heraeus poiymerization shrinkage ofthe composite resinJ Kuizer, Wehrheim, Germany), Standard inlay cavi- Inserting highly precise inlays with the above- ties were cut using a high-speed handpiece mentioned technique is a probiem, however, be- (Kaltenbach & Voigt, an der Riß, Germany) cause the fiim thickness of the bonding resin will and Cerinlay diamond burs (Intensiv, Viganelio- not allow the inlay to be fully seated into the cav- Lugano, Switzerland) with abundant water cooling. jty 19,30 The film thickness of dentin bonding agents The cavity form is shown in Fig 1. The teeth were is in the range of 60 tc 350 pm if they are cured randomly distributed into four groups (Fig 2) and immediately after application onto the prepared ceramic iniays were produced, 16 with the Empress tooth,1^ Van Meerbeek et al^o measured the fiim glass-ceramic procedure, using a high-pressure thickness of Scotchbond adhesive and found val- casting machine (Ivoclar, Schaan, ), ues from 50 tc 500 pm. Peter et ai^i have reported and 16 with the Cerec II machine (Sirona Dental that at the transition of vertical to horizontal cavity Systems, Bensheim, Germany), which ailows a de- wails, the thickness of bonding resin may reach fined imprecision of the iniays by setting the ce- 200 |jm. Therefore, clinician's work is usually com- ment film width to a high value. promised by not light curing the bonding resin be- The teeth were mounted into the measuring gauge fore insertion ofthe iniay. However, it is not known (iViillitast, Perthen Mahr, , Ger- if such a procedure would hamper the margin qual- many) (Fig 3) with a iight-cured composite to assure ity of the restoration. their compiete fixation. The inlays were then tried in The purpose of this study was to measure the in- and the gauge was set to 0. After cementation with fluence of a modified and simplified insertion tech- two different adhesive techniques, the vertical di- nique for ceramic inlays on the fit and the margin mension change in microns was read on the dial of quality of the inlays. the measuring gauge. The following regimens for

160 The Journal of Adhesive Dentistry 32 human premolars

16 Empress inlays 16 Empress inlays

Fit measuring with Millitast (difference "try in-cemented"}

Etch & Prime 3.0 Etch & Prime 3,0 Etch & Prime 3.0 Etch & Prime 3,0

Light curing 20s Light curing 20s

Varioiink II + Varioiink II Varioiink II + Varioiink II + inlay inlay iniay inlay

Light curing 60s Light curing 60s Light curing 60s Light curing 60s

Fit measuring with Millitast

24h water storage

1, replica

thermocyoiing

2. replica

quantitative margin analysis (SEM 200x)

Statistical evaluation

Experimental design.

the adhesive technique were used: in all groups was then carried out for 3 minutes at 100°C in the Etch & Prime 3,0 (Degussa, Hanau, Germany) was Dry Tec stove (Dentspiy DeTrey, , Ger- applied with a small brush for 30 seconds. It was many), then blown dry for 5 seconds and a second applica- The inlays were inserted with Varioiink il (Vi- tion was done as previousiy described. In groups 1 vadent Dental, Ellwangen, Germany) and, after and 3 the bonding resin was iight cured for 20 sec- careful removai of aii luting composite excess with onds with an Optiiux 400 light unit (Demetron Re- Kerr appiicators (Flexible Disposable Applicator, search, Danbury, CT, USA) after every application. Kerr Manufacturing, Romulus, Ml, USA) and appli- All inlays were etched for 90 sedondB with 10% hy- cation of a glycerin gei (Airbiock, Dentspiy DeTrey, drofluoric acid gel (Vita Ceramics etch. Vita Zahn- Konstanz, Germany), the composite was cured for fabrik. Bad Säckingen, Germany), rinsed, dried, and 60 seconds on the occiusai surface and 20 sec- silanated with a 2.5% MPS soiution (Rosiian, lOB onds on each side. Chemie, Berlin, Germany) for 5 minutes). Drying

Voll, No 2,1999 _ 161 Clotten et ai

After the second measurement with the measur- ing gauge, the margins were polished with alu- minum oxide-coated flexible discs (Sofiex, 3M, St Paul, MN, USA) and an abundance of water. The teeth were then immersed in water for 24 hours.^° Replicas were obtained by taking impressions with a poiyvinylsiloxane impression material (Siia- gum, Dental-Material Geseilschaft, , Ger- many), which were cast with an epoxy resin {Stycast 1266 Part A and B, Emerson & Cuming, Westerio, Beigium). Into the still soft resin, SEM holders were mounted on the repiicas and a quantitative margin analysis^B was performed in the SEi\i1 at a magnifi- cation of 200x using the criteria depicted in Figs 4 and 5. Oniy the tooth-iuting composite interface was evaiuated, but the finishing iines in enamei and in dentin were recorded separately. The data of the fit test were anaiyzed statisticaiiy with an ANOVA, and the data ofthe margin analysis with the Friedman and Wiicoxon test using the SPSS program (SPSS PO +, Version 2.0, SPSS GmbH, Munich, Germany).

RESULTS

The results of the fit test are given in Fig 6. Note that in all cases the inlays were more than 5 pm deeper in the cavities after the luting procedure. Fig 3 Eieotronic measuring gauge for the "fit" experiment. Figures 7 and 8 show the results of the margin The position of the inlay was recorded at try-in and after ce- anaiysis. Note that there was no statistical differ- mentation. ence between the different groups. In all cases, margin qualities with high amounts of "excellent margins" and iow values of "marginai openings" were found. A larger scatter of the data was ob- served with the enamel margins.

DISCUSSION

The method of using a precision gauge to deter- mine the fit of inlays after cementation has already been used successfuiiy in another study.i^ We mod- ified it by firmiy mounting the teeth into the device with a iight-cured composite (Master Tray, Dr. Ihde Dental, Uetliburg, Switzerland) with the positive re- sult that the standard deviation was significantly decreased. The quantitative margin analysis in the Fig 4 Evaluation oriteria. SEM is a standard tool for the assessment of resto- rations and is widely used in similar studies. With the use of replicas, there is no danger of artifacts

162 The Journal of Adhesive Dentistry CIctten et ai igs 5a to 5f Examples for the evaluation criteria (SEM, magnification x200).

Fig 5a Excellent margin: Smooth transition of enamel-luting Fig 5b Minor discrepancies at the luting composite-enamel composite-inlay, interface.

[) = SMALL MARGINALOPEHING COIiPOSITEIIIILAr C= SLIGHTSUBMARGINAtlON INUYICOWPOSitEIDENTIN ZBE Fig 5(1 Smail marginal opening (luting composite-dentin inter- Frg 5c Slight submargination (inlay-luting composite-dentin face).

163 Vol 1, No 2, 1999 Ciotten et al

E ^ LARGE FMARCINAL OPENIMG COMPOSITEJENAMEL

Fig 5e Large marginai opening (luting composite-enamel in- Flg5f Overhang (luting composite-dentin interface). terface).

due to the needed dessioation for the work in the SEM. The adhesive system Etch & Prime 3.0 was cho- sen for two reasons: First, it has a very low viscos- ity. Therefore, we expected a low film thickness, even if it was polymerized before insertion of the in- lays. Second, being a universal bonding system it provides further simplification of the inlay insertion procedure, in that enamel etching and subsequent rinsing can be omitted. The luting composite excess was removed with Kerr applicators. Using magnifying glasses (5x mag- nification, Zeiss, Germany) operator errors seen as submargination (criterion C) and overhangs (crite- rion F) could be minimized to a negligible level. Therefore, they were not reported in the results table. Cerec Cerec Empress Err>press bonding boruJing Bonamg bondirg The technique used in this In vitro experiment rvotcufed cursd no] cured curad was taken from the regular clinical procedures used Fig 6 Differences ofthe position ofthe iniays in the cavity be- to cement inlays with adhesives. Therefore, poly- tween the try-in measurement and after cementation. The merization was performed on the occlusal and box piots show the median, the 25"^ percentiie, and the 75th proximal surfaces. Doing this, one oan expect to percentile. The t bars indicate the 5'^ and the 95'*' per- ce hti I es. create identical pathways of polymerization shrink- age as in the real clinical situation. Cerec inlays were used because the machine gives the option of deliberate imprecision, enabling

164 TheJournal of Adhesive Dentistry Clottet

exceiient margin axcellent •narglti

marginal openitig

Fig 7 Quantitative margin analysis of the enamel fihishing Fig 8 Quantitative margin analysis of the dentin finishini lires (box plots) (P> 0.05). lines (ÖOX plots) (P> 0.05).

us to compare our data with former studies in of composite are polymerized and thus low polymer- which Cerec iniays were successfully inserted into ization shrinkage effects are expected. With the fin- cavities with cervicai finishing lines in dentin.^e The ishing iines in enamel, we observed some larger Empress system was selected because, in our expe- scatter of the data in some groups, but none that rience, glass-ceramic inlays show the best precision were statistically significant. This fact may iead to fit. 15 the suspicion that Etch & Prime 3,0 is siightiy less After cementation, the inlays were approximately effective on enamei, which could be explained by 10 pm deeper in the cavity than at the try-in ses- the fact that enamel is more difficult than dentin to sion. This can be explained by the substance ioss etch with Etch & Prime 3,0, This shallow etching created in the ceramic by etching. Since there were pattern may be a result of either deficient penetra- no differences between the polymerized and the tion of the self-etching primer into the enamel mi- unpolymerized layers of the bonding agent, it can croporosities^'^ or precipitation of calcium on the be concluded that Etch & Prime 3.0 is able to pro- enamel surface, masks the etch pattern and inter- duce ultrathin iayers. We have no explanation as to feres with resin penetration.^ Whether the acidic why the Cerec iniays that were cemented into cavi- components of this adhesive system are as effect- ties without a separate light curing were signifi- ive as the acid-etch technique for creating a reten- cantly deeper in the cavities than all the other tive etching pattern in enamel should be inlays. We would have expected the same to be true investigated in a future study. for the Empress inlays treated the same way as weli. The good margin quality, characterized by high CONCLUSION amounts of "excellent margin" and virtually the ab- sence of "marginal openings" observed with all Within the limits of this in vitro study it can be con- groups for the dentin finishing lines shows that the cluded that Etch & Prime 3.0 is an effective bond- Etch & Prime 3,0 bonding system is effective on ing agent for dentin and enamel in conjuncticn with dentin in combination with inlays, where thin layers ceramic inlays. Furthermore, the timing of the light

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165 TheJournai of Adhesive Dentistry