Interfacial Micromorphoiogy and TensiieBond Strengtii of Dentin Bonding Systems

after NaOCi Treatment

Thomas PiochVSedin KobasIijaVBrunhild SchagenVHermann

Purpose: The objective of this study was to test the hypothesis that NaOCi treatment of acid-etched dentin

would not lower the tensile bond strength of adhesive resins, but would eliminate the hybrid layer.

Materials and Methods: One hundred twenty teeth and three different bonding agents were used for

SEM- and CLSM-visualization of the dentin-oomposite interface and for bond strength measurements.

After etching with phosphoric acid, 75 dentin samples were pretreated with 10% MaOCI. The other 75

samples were etched only with phosphoric acid and were kept as controls. Composite was bonded to the

pretreated surfaces with a bonding resin.

Results: NaOCI-treated samples: hybrid layers were not visible, but resin tags and resin penetrationthrough lateral branches of tubuies were prominent. Layers of unfilled resin were not apparent for GlumaCPS and Prime & Bond 2,1 , Hypochlorite treatment of acid-etched dentin resulted in reduced bondstrengths for specimens bonded with Syntac and Gluma CPS, but such treatment increased bond strengthfor Prime & Bond 2,1 bonded specimens.

Conclusion: The removal of the collagen layer with NaOCI oan enhance or decrease bond strengths, de-

pending on the bonding agent used,

J Aijhesive Dent 1999:2:135-142 Sijúmitted for puiDlication: 11.12.98: accepted for publication: 22.02.99

It is well known that resin bond strength to dentinoccurs through resin infiitration of dentin. The in-

filtration zone is calied the hybrid layer. The bond-ing mechanism is mainly based on micromeohanioalretention. The hybrid iayer, resin tags, and adhesivefiiiing of lateral branches of dentinai tubuies havebeen suggested as the essentiai mechanisms ofadhesion. The most important factor should be thehybridization between resin and demineralized col-lagen. However, severai groups have speculated

^ Lecturer, Department of Restorative Dentistry ¡Director: Prof. Or.Dr. HJ. Staehie), University ot Heiáeiberg, Germany

" Clinical Assistant, Stomatological Faculty of Sarajevo (Director:Prof. Dr. sei. Hamiú Tahmiscija), Bosnia and Herzegovina

" rechnicat Assistant, Department of Restorative Dentistry (Director:Prof. Dr. Dr. H.J. Staehlej, University of Heidelberg,, iSermany

" Physicist, Institute for Applied Structure- and Microanalysis (Direc-tor: Prof. Dr. H. Duschnerj, University of iVIainz, Germany

Reprint requests: Priv.-Doz Dr Thomas Pioch, University of Heidel-berg, Department of Restorative Dentistry, Im NeuenheimerFeld 400, f}-69120 Heidelberg, Germany Fan +49-6221-565074.e-maii:thornas_pioüh®meíl.uni-heiílelberg.de

that the demineraiized zone, namely a coiiagen net-work, may not contribute directly to bond strength.Between unaltered dentin and the superficiai colla-gen-rich fibrous network is a zone of partiallydemineraiized dentin. Gwinnett''^^ concluded thatoptimal bond strength between a restoration andacid-conditioned dentin is dependent upon diffu-sion of the resin components of the bonding systemthrough the outermost demineraiized, collagen-richzone into the partially demineralized zone below, inwhich it must polymerize. Thus, the totally deminer-alized zone may not contribute directly to the inter-facial strength. Any collapse of the collagen matrixas a resuit of overdrying might prevent monomersfrom penetrating into deeper areas and increasethe risk of adhesive faiiures. Therefore, relativelythick hybrid layers, which can be achieved by over-etching, may decrease bond strength.^^ Recent re-search has aiso focussed on the durabiiity of thebond^'i^ and the existence of "nanoleakage"i8 as aresuit of incomplete penetration of resin into thedemineralized dentin. Deterioration of adhesion

Vol 1. No 2,1999 135

and resultant decreases in bond strength in thelong term have been reported. Nakabayashi et alsuggested that this deterioration is due to degrada-tion of accessible coiiagen peptides in the layer ofdemineraiized dentin between unaitered dentin andthe hybrid layer.12 jhis unsupported layer of colla-gen is the result of an inability of the adhesive resinto fiow to the base of the demineraiized area.22Several researchers have pointed out that removaiof the collagen network at the interfaciai region byusing sodium hypochiorite might not influence bondstrength.8.9 other authors reported that such treat-ment improved the interfacial strength,^o-^" Thisleads to the question about the necessity of a hy-brid layer for resin-dentin bond strength. There areother effects of NaOCi on the dentin-puip compiexwhich should be considered in this context. Blunci^et ai2 reported that there was no decrease of mar-ginai adaptation after a pretreatment of cavity wallswith 10% NaOCi for 60 s. Using silver nitrate as apenetration agent, Kobaslija did not find any evi-dence of nanoieakage after removing the coiiagenfrom acid-etched dent inal surfaces with 10%sodium hypochiorite.11 Shear tests indicated thatthe cohesive strength of dentin is not reduced afterimmersion in 5% NaOC!.^^ From a crystallographicviewpoint, crystals in the NaOCI-treated dentin aresimiiar to enamei crystais.^^ iHowever, an explana-tion ofthe mechanism of resin-dentin bonding with-out hybridization of demineraiized coiiagen isunclear. Therefore, this study focussed on the inter-faciai morphology using scanning electron mi-croscopy (SEM) and confocai laser scanningmicroscopy (CLSM). The purpose of this study wasto test the hypothesis that NaOCI treatment of acid-etched dentin wouid not lower the tensile bondstrength of resin, even though it wouid eliminate aconventionai hybrid layer, it was hoped that SEiVIand CLSM examination of the interface of the resin-dentin bonds would reveai the mechanism of bondstrength in the absence of a hybrid iayer.

MATERIALS AND IVIETHODS

One hundred twenty human moiars, free of caries,restorations, cracks, and obvious defects werestored in 50% ethanol at 8° C for a maximum of 1month following extraction in order to avoid micro-bial contamination. This storage medium was cho-sen because it produces iittle change in dentinpermeability,^

Prior to the experiments, the teeth were piacedin water for 24 hours at 20" C. The roots of ail teethwere piaced in a self-poiymerizing resin (Paladjrtransparent, Kuizer, Wehrheiin, Germany). Ninetyteeth were prepared for bond strength tests by re-moving the occlusal enamel and exposing freshdentin using a microtome saw (Leica 1600, Ben-sheim, Germany) under continuous water coding.For the micromorphological investigation, dentindisks with a thickess of 2 mm were prepared fromthe other 30 teeth. The dentin of all specimens wasexposed at a ievel approximateiy haif-way betweenthe pulp chamber and the enamel, perpendicuiar tothe tooth axis. The exposed dentin surfaces wereprepared with 500-grit wet silicon carbide abrasivepaper for 15 seconds. Three commercially availabledentin bonding agents were used aiong with theirrecommended composite materiais, according tothe manufacturers' instructions (Table 1). For CLSivlinvestigaticn, the primers were mixed with the fluo-rescent dye Rhodamin B isothiocyanate (E. iVlerck,Darmstadt, Germany; approximate concentration0.1%; maximum absorption = 540 nm; maximumemission = 625 nm). The light output of the visibielight-curing unit was monitored to be greater than400 mW/cm^.

For bonding with the Syntac system (Ivociar-Vi-vadent, Schaan, Liechtenstein), the dentin surfacesof 30 teeth were etched for 15 s {Email PreparatorGS) and another group of 10 disks for 30 s. The sur-faces were rinsed with water spray for 15 s. In addi-tion, 15 of these acid-etched teeth and 5 diskswere treated with a 10% sodium hypochiorite solu-tion for 60 s using a cotton pellet and rinsed withwater for 60 s, ieaving a moist dentin surface. Theprimer was applied using a brush and ieft undis-turbed for 15 s. The primed surface was dried witha gentle air stream. The adhesive was appiied witha brush, and after 10 s, it was air dried. The unfiliedresin Heiiobond {component of the Syntac system)was applied with a brush. Excess iiquid was blownoff with air. The bonding agent was iightcured for10 s.

For Gluma CPS (Bayer Dental, Leverkusen,Germany), 30 dentin surfaces and 10 disks wereetched for 30 s (Conditioner CPS), washed withwater spray, and dried with air. Fifteen of theseteeth and 5 disks were treated with a 10% sodiumhypochiorite solution for 60 s using a cotton pelletand rinsed with water for 60 s, leaving a moistdentin surface. The primer was applied with abrush and left undisturbed for 30 s. The surface

136 The Journai of Adhesive Dentistry

Picch étal

Table 1 Restorative materiais used in this study

Syntac

Gluma CPS

Primer

TEGDMA, 4% maieicacid, water, acetone

HEMA, 5%glutaraldebyde, water

Prime & Bond 2,1 PENTA, TEGDMA,acetone

Unfilled resin

PEGDMA, 5%glutaraldehyde, water

Poiyfunctionalmetbacrylic esters

Composite

Tetric

Pekafil

Spectrum TPH

was dried thoroughly with an air stream. The adhe-sive (sealer) was applied in a thin layer with a brushand was spread by a gentle air stream.

For Prime & Bond 2.1 (Dentspiy De Trey, Kon-stanz, Germany], dentin surfaces of 30 teeth wereetched for 15 s (De Trey Conditioner 36) and 10disks were etched for 30 s. The surfaces wererinsed with water spray for 15 s. Fifteen of theseteeth and 5 disks were treated with a 10% sodiumhypochlorite solution for 60 s using a cotton pelletand rinsed with water for 60 s, leaving a moist den-tin surface. The adhesive was applied to the dentinsurface with a brush and left undisturbed for 30 s.Excess solvent was removed with compressed air,and the adhesive was light-cured for 10 s. Onemore layer of adhesive was applied, the solvent wasremoved immediately, and again the adhesive waslight-cured for 10 s.

The prepared disks (n = 30) were embedded inmethacryiate resin (Paladur transparent, KuUer,Wehrheim, Germany) and vertically sectioned intohalves, approximately parallel to the tooth axis,using a water-cooled microtome saw. One half ofeach disk was used for examination under SEM andthe ether half for CLSM.

SEM Investigation

The sectioned surface of each sample was groundwith silicon carbide abrasive paper of 1200 grit,using running water as a lubricant, and rinsed indistilled water. The samples were then etched with5% phosphoric acid for 1 min to remove the smearlayer and bring the interface into relief by partialdissolution ofthe dentin. The specimens were dehy-drated through ascending grades of ethanols, air

dried and sputter-coated with a layer of gold (30nm}. The SEM used was the Amray lS lO (Bedford,MA, USA),

CLSM investigation

Prior to CLSM inspection, the specimens werestored in water for 24 h at 20° C and kept humidthroughout the whole experiment. The measure-ments were carried out with a Leica Diaplan GLSM(Leica, Heidelberg, Germany) equipped with oil im-mersion objectives (lOOx; NA = 1.3) and an Ar/Kr-mixed gas laser source (adjustable up to 40 mW),In the fluorescent mode, the laser was operatedwith a 510 nm short pass filter (maximum excita-tion at 488 nm]. The fluorescence from the speci-mens was discr iminated from reflected andscattered light by a 530 nm long pass filter, Histo-tomograpic images (parallel to the surfaces) wererecorded within the specimens, 10 pm beneath thesurface.

Tensile Bond Strength Measurements

After applying the adhesive systems to the dentinsurfaces, two layers of the recommended compos-ite resin (1 mm each) were applied within the cavityof a metal funnel (circular cross-section of 12.6mm^; 10 mm high). Each layer was light-cured for20 s. Then, the samples were stored in water at20° C for 24 h. Tensile bond strengths of the adhe-sive systems were tested with a testing machine(Zwick 1120, Ulm, Germany} at a crosshead speedof 5 mm/minute.

Vol 1, No 2,1999 137

Pioch et ai

Fig 1 Top view of a specimen treated with NaOCI for 1 minuteafter acid conditioning. No organic elements can be obsen/edin this picture.

Fig 2 SEM image of a cross-section of the interface betweenSyntac and dentin substrate treated with phosphoric acid. Vis-ibie layers are composite, unfilled resin, hybrid iayer (arroivjand dentin.

Fig 3 SEM image of a cross-section of the interface betweenGluma CPS and dentin substrate treated with phosphoric acidand NaOCI. There is no evidence of a hybrid layer, and no gapformation.

Fig 4 SEM image of a cross-section of the interface betweenPrime & Bond 2.1 and dentin substrate treated with phos-phoric acid and hJaOCi. There is no evidence ot a hybrid layer,and no gap formation.

Statistics

Differences in bond strengths between control andNaOCI treatment groups within each bonding agentwere tested using the Mann-Whitney U-test at the5% level.

RESULTS

SEM and CLSM InvestlgaUons

Eigure 1 shows a top view of a specimeh treatedwith 10% NaOCI for 1 minute after acid condition-ing. Mo collagen fibers can be observed. Under SEM

observation, the hybrid layer was seen as an acid-resistant zone located at the dentin-resin junction.After the use of Syntac, Figure 2 shows the hybridlayer (indicated by ah arrow) as an acid-resistantzone. All the control specimens (not treated withNaOCI] from the three bonding agents tested showedsuch a hybrid layer. Images from the other bondingsystems used are similar to Fig 2. In contrast tcthis, SEM images from all specimens pretreatedwith NaOCI give no evidence of such a hybrid layer(Figures 3 and 4). Under CLSM observation, thefluorescent dye can be seen to be distributed withihthe intertubular dentin of the control groups (Fig-ures 5a, 6a, 7a) as a result of the resin which haspenetrated the demineralized zone. Resin tags can

138 The Journal of Adhesive Dentistry

Fig 5a CL5M image of a cross-seotion of the interface be-tween Prime & Bond 2.1 and dentin substrate treated vjjthphosphoric acid. A hybrid layer is visible. Note fhe relativelysmall diameter ofthe resin tags.

Fig 5b CLSM image of a cross-section of the ihtetface be-tween Prime & Bohd 2.1 and dentin substrate treated vfithphosphoric acid and MaOCI. A hybrid layer is not visible. Notethe larger diameter ofthe tesin tags.

Fig 6a CLSM image of a oross-section of the interface be-tween Syntac and dentin substrate treated with phosphoricacid. A hybrid layer is visible.

Fig Gb CLSM image of a cross-section of the interface be-tween Syntac and dentih substrate treated with phosphoricacid and NaOCI, A hybrid layer is not visible.

Fig 7a CLSM image of a cross-section of the interface be-tween Gluma CPS and dentin substrate treated with phos-phoric acid. A hybrid layer is visible.

Fig 7b CLSM image of a cross-section of the interface be-tv^een Gluma CPS and dentin substrate treated with phos-phoric acid and NaOCI. A hybrid layer is not visible. Note thepresence of filler particles in the resin tags.

Vol l , No 2,1999 139

Table 2 Tensile bond strength for each procedure

Syntac

After H3PCJ 3,89 ± 3,47 MPaAfter H3PO4 and NaOCI 1,78 ± 1.43 MPaStatistics (U test) p - 0,037

n — 15 in each Group

Gluma CPS

6,57 ± 3,53 MPa2.57 * 2.91 MPap = 0,035

Prime&Bond 2,1

4,06 ±2,22 MPa7,35 ±4.57 MPap = 0,053

also be visualized because of the dye mixed withthe resin. In contrast to this, CLSiVi images from allspecimens after pretreatment with NaOCI do notshow such a hybrid layer ¡Figures 5b, 6b, 7b), Nei-ther an acid-resistant zone nor an intertubuiar pen-etration can be interpreted from these images,instead, there were larger resin tags. Resin compos-ite (including fiiler particies) penetrated into theopenings of the tubules. More anastomoses can beobserved when compared to the specimens wheredentin was treated with phosphoric aoid aione. Lay-ers of unfiiied resin were not apparent for GlumaCPS and Prime & Bond 2 .1 , The iayer of collagenfibers hybridized with resin, which was seen in con-troi specimens, is not apparent after the treatmentwith 10% NaOCI for 60 s.

Bond Strengtii Measurements

Tensile bond strengths for dentin are summarizedin Table 2 according to the treatment procedure.For Syntac and Gluma, the values of the NaOCigroup are lower in comparison to their controigroups. For Prime & Bond 2 , 1 , the vaiues afterNaOCI treatment increased, in the case of Syntacand Gluma, the differences are statisticaiiy signifi-cant at a 5%levei (Mann-Whitney U-test).

DISCUSSION

The chemical integrity between hydrophiiic dentinand hydrophobic resin is not compatible. In order toachieve hybridization between dentin and resin,water-compatible monomers are used which areabie to polymerize with resin composite and pene-trate the moist, demineraiized dentin. On the other

hand, solvents like acetone and alcohol penetratethe dentin surface and help reduce its hydrophiiiccharacter. Therefore, the control specimens fromthe three different bonding agents tested (not pre-treated with sodium hypochiorite) showed a weil-de-veloped hybrid layer. This is well known from theiiterature.3ri3,i5,i6,23,26 ji^g use of sodium hypo-chlorite removes the totaiiy demineraiized coiiagennetwork, aiters the dehtin surface, and mightchange the hydrophiiic properties. From this pointof view, the sodium-hypochlorite-treated dentinmight be more compatible with hydrophobic resinsthan acid-etched dentin. On the other hand, the in-filtration zone of demineralized dentin and resinmonomers has been cited as the most effective ad-hesion component.25 However, this hybrid layer isno ionger apparent after treatment with NaOCi.Under these conditions, the resin bonding mecha-nism must be mainiy based on the infiltration ofresin into the partiaiiy demineralized dentin, andinto the dentinai tubules and their branches, A sur-face interaction zone of resin which penetrated intothe partially demineraiized and deproteinized iayermight provide resin retention. This bonding mecha-nism was suggested by Gwinnett,^ but it cannot bederived from the literature or our SEM or CLSM im-ages. Because of the iimited resolution of theCLSM, which is an improvement over conventionailight microscopy by oniy ca, 200 nm laterally,^^'26,27the detection of porosities within partially deminer-alized dentih cannot be expected. Neither is theSEM technique used in this study able to identifysuch a hypothetical layer, in spite of this, the SEMand CLSM results demonstrated that such a hy-bridization between resin and the partially deminer-alized and deproteinized zone was, if present at ail,thinner than 0,2 um, if hybridization between resinand partiaiiy demineralized and deproteinized

140 The Journal of Adhesive Dentistry

dentin can be obtained by other methods, the ex-pression "hybrid layer" needs to be redefined.

Tensile bond strength measurements indicatethat a reduction of bond strength is not generaiiy aconsequence of a pretreatment by NaOCi. Bondstrength results from the literature are not uniform.it was reported that after acid etching, bondstrengths improved after a NaOCi treatment,S-20.24bond strength was lower,̂ and that such a treat-ment does not play a statistically significant role.̂ 'SInai et al^ and Gwinnett^ found an increase ofshear bond strength using acetone-containingprimers and a decrease in the case of primerswhich do not have acetone as a solvent. Due totheir relatively high volatiiity, solvents such as ace-tone and, to a lesser degree, ethanoi, may displacesurface moisture and serve to better carry theprimer monomers into the micro- or nanoporositiesofthe exposed collagen network.lO Bond strengthis due, in part, to the diameter, number, andstrength ofthe resin tags.25 Looking at Figs 3 to 7b,it can be conciuded that these tags have very largediameters after treatment with NaOCi, permittingfiller particies to reinforce and strengthen them. Itshould be borne in mind that commercialiy-avail-able bonding systems are not optimized for adhe-sion to NaOCI-treated dentin surfaces. Curmorphological results confirm those mentioned inthe literature,S'9 which state that after NaOCI treat-ment, resin tags are weii established and moretubuiar anastomoses are observed when comparedto the control specimens, where dentin was treatedwith phosphoric acid alone. In shear tests, thesetags are cut by the shearing force. In the case oftensile tests, tags are either pulled out of thedentin tubules or broken. Thus, it must be takeninto consideration that both the type of bondstrength test and tubule orientation might infiuencethe resuits.is In addition, because there are widevariations in testing procedures, bond strength vai-ues cannot be compared between different re-search groups. Our reiativeiy low tensile bondstrengths are based on a large bonding area of12.6 mm .̂ The influence of polymerization shrink-age and the ability of the system to compensate formechanical polymerization stressai in our test aremore effective as compared to smaller bondingareas, Debonded surfaces have been investigatedby SEM, as described eisewhere.^i The anaiysis offailure modes showed that about 80% were adhe-sive failures. However, the tensile bond strengthvalues presented in this study are qualitatively simi-

lar to those of Inai et al.9 In this study, the NaOCIconcentration was higher than would be used ciini-caiiy. Although some advantages of an additionalNaOCI treatment after acid etching can be statednow, the parameters of treatment and the formula-tion of primer materials should be optimized priorto its clinical use.

ACKNOWLEDGMENTS

Thib investigalion was îupporled by the Geraian Research Founda-tion (Deutsche Forschungsgemeinschafl) Research Grant STA394/2-1.

REFERENCES

1. Alhadainy HA, Abdalia Ai. 2-year clinjcai evaiuslion of dentinbonding systems. Am J Dent 1996;9:77-79.

2. Biunck U, Speyer F, fioulet JF. Effect of hypbchlorite treatmentof conditioned dentin on the marginal adaptation of compos-ite resin restorations [aOstract 46]. J Dent Res 1997;76.

3. D'Souza PD, Duschner H, Staehie HJ, Pioch T. Dentin bondingsystems: a comparative study of SEM and CLSM used to visu-aiize the resin-dentin interface. Acta Med Dent iHelv 1999:4:20-26.

4. Ferrari M, Wannocci F, Vichi A, Davidson CL. Effect ot twoetching times on the sealing ability of Ciearfii Liner Bond 2 inclass V restorations. Am J Dent 1997;10:66-70

5. Franhenberger R. Obersciiacintsiei< h, Sindei J, Kramer N.Petschelt A. Push-out dentin bond strength of modern adhe-sives after NaOCI.pretreatment [abstract 1469]. J Dent Res1998 J 7.

6. Goodis HE, Marshaii GW, White JM. The effects of storageafter extraction of the teeth on human dentine permeabilityin vitro. Archs Oral Bioi 1991:36:561-566.

7. Gwinnett AJ. Dentin bond strength after air drying and rewet-ting. Am J Dent 1994:7:144-148.

8. Gwinnett AJ. Aitered tissue contribution to interfaciai bondstrength with aoid oonditiohed dehtin. Am J Dent 1994:7:243-246.

9. Inai N, Kanemura N, Tagami J. Watanabe LG, Marshall SJ,Marshail GW, Adhesion between coiiagen depieted dentinand dentin adhesives. Am J Dent 1998:11:123-127.

10. Kanoa J. Effect of resin primer soivents and surface wetnesson resin composite bond strength to dentih. Am J Dent1992:5:213-215.

11. Kobaslija S. Evaiuation of dentine adhesive's micromeohani-cai bond to dentai structures conditioned with NaOCI (disser-tation). University of Sarajevo, 1999.

12. Nakabayashi N, Ashizawa M, Nakamura M. Identification of aresin-dentin hybrid layer in vitai human oentin created invivo: durabie bonding to vital dentin. Quintessence int1992:23:135-141.

13. Perdigao J, Swift EJ, Denehy GE, Wefel JS, Donly KJ. In vitrobond strengths and SEM evaiuation of dentin bonding sys-tems to different dentin substrates. J Dent Res 1994:73:44-55.

Voi 1, No 2, 1 9 9 9 141

Pioch et al

14, Piocb T, Staehle HJ, Expérimentai investigation of the shearstrengths of teeth in the region of the dentinoenamei junc-tion. Quintessence Int 1996;27:711-714,

15, Pioch T, Stotz S, Staebie HJ, Duschner H, Apclications of con-fcoal laset scanning microsGCpy tc dental bending, Adv DentRes 1997;11:453-461,

16, Pioch T, Stotz S, Buff E, Duschner H, Staehle HJ, influence ofdifferent etcbing times on hybrid layer formation and tensilebond strength. Am J Dent 1998:11:202-206,

17, Sakae T, Mishima H, Kozawa Y, Changes in bovine dentinmineral with sodium bypccblorite treatment, J Dent Res1988:67:1229-1234,

18, Sano H, Takatsu T, Ciucchi B, Herner JA, Mattews WG, Pash-ley DH, Nanoleakage: Leakage within tbe hybrid iayer, OperDent 1995:20:18-25,

19, Schüpbach P, Krejci I, Lutz F, Dentin bonding:effect of tubuleorientaticn on hybrid-layer formation, Eur J Orai Sci 1997;105:344-352.

20, Takana J, Nakai H, Application of root canal cleaning agentshaving dissoiving abiiities of coiiagen to the surface treat-ment for enhanced bonding cf resin tc dentin. Dent Mat J1993:12:196-208,

21, Une S, Finger WJ, Function of the Iiybrid zone as a stress-ab-sorbing layer in resin-dentin bonding. Quintessence int1995:26:733-738,

22, Van Meerbeek B, Inolioshi S, Braem M, Lambrechts P, Van-tierle G, Mcrpbclogical aspects of the resin-dentin interdiffu-sion zone with different dentin adhesive systems, J Dent Res1992;71:1530-1540.

23, Vargas MA, Sobb DS, Armstrong SR, Resin-dentin shear bondstrength and interfacial ultrastructure with and without a hy-Orid layer, Oper Dent 1997;22:159-166,

24, Wakabayashi Y, Kondou Y, Suzuki K, Yatani H, Yamashita A,Effect of dissoiution of collagen on adbesicn to dentin, intJProsthodont 1994:7:302-306,

25, Waistiaw PR, McComb D, Clinical ccnsideraticns fcr optimaidentinal bonding. Quintessence Int 1996:27:619-625,

26, Watson TF, Boyde A, The use of fiuorescent markers forstudying tbe distributicn cf a dentine bending agent betweena ccmpcsite restoration and tootb. Clin Mater 1987;2:33-43,

27, Watson TF, Fact and artefact in confocal microscopy, AdvDent Res 1997:11:433-441,

Cerinlay Setby Prof. J, F. Roulet and Dr. S. Herder, University of Berlin

The means to ideal inlaycavity preparations

Due to the slight tupering uncithe small diameter, minimaltuoth substance is removed andundercuts are avoided. TheCerinlay Set is ideal for prenio-lurs jud molars. All ceramicinla} preparation demands canbe easily met.

Ceramic inlay preparationsshonid he simple, distinct andhave roimded interior edges.Preparation with the 80 |im gritdiamonds is efficient and thecavity form is correct for cera-mic inlays.

The finishing diamonds(25 pm), vvhiih have the sameshape, are used to carefullysmoothen the enamel margins.

PLEASE CONTACT

OUR MARKETING DEPARTMENThíXp:l/www. in tensiv.chE-maU:intensiv.sa®biuewin.ch

Intensiv SA

Via al Molino 107, RO.ßox 741CH-6916 Grancia

142 The Journal of Adhesive Dentistry