Critical Appraisal

OPTIONS FOR DENTIN/ENAMEL BONDING: PART IIIjerd_338 200..205

Author and Associate Editor

Edward J. Swift Jr., DMD, MS*

Four categories of resin-based dentin/enamel adhesives are currently available. These includethe three-step etch-&-rinse, “one-bottle” etch-&-rinse, two-step self-etch primer systems, and

“all-in-one” self-etch adhesives. In consecutive issues of the Journal, the Critical Appraisal seriesis presenting salient publications on research in each of the categories. The first two installmentsfocused on the etch-&-rinse systems. The series continues with this review of papers on thetwo-step self-etch primer systems.

U LT R A S T R U C T U R A L C O R R E L AT E S O F I N V I V O / I N V I T R O B O N D D E G R A D AT I O N I NS E L F - E T C H A D H E S I V E S

N. Donmez, S. Belli, D.H. Pashley, F.R. TayJournal of Dental Research (2005;84:355–9)

A B S T R A C T

Objective: The objectives of thisstudy were (1) to evaluate the invitro and in vivo bond durabilityof two self-etch adhesive systems,and (2) to characterize morpho-logical changes in resin-dentininterfaces aged in the oral environ-ment and under laboratory condi-tions for 1 year.

Materials and Methods: For the invivo portion of the study, patientswith one or more erupted, unre-stored third molars scheduled forextraction were selected. Class Ipreparations were made in 24teeth under rubber dam isolation.

The teeth were randomly dividedinto two groups for bonding witheither Clearfil SE Bond or ClearfilProtect Bond (both Kuraray,Tokyo, Japan). Both systemsinclude a mildly acidic self-etchprimer. These are similar materi-als, but Protect Bond containsan antibacterial monomer andincludes a fluoride-releasingbonding agent. The preparationswere restored using a thinflowable resin liner and twoincrements of a light-activatedhybrid composite.

The adhesive groups were dividedinto two sub-groups based on

extraction time—24 hours or 1year following restoration. Afterextraction at each time, fourteeth from each group were sec-tioned for microtensile bondstrength (mTBS) testing, which wasaccomplished using a universaltesting machine.

To compare bond degradationin vivo and in vitro, the samerestorative procedures were donein 25 extracted third molars.The restored teeth were storedin artificial saliva at 37°C, andwere retrieved and sectioned formTBS testing at 24 hours or1 year.

*Professor and Chair, Department of Operative Dentistry,University of North Carolina School of Dentistry, Chapel Hill, NC 27599-7450, USA

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Two specimens from each in vivoand in vitro group were processedfor examination with transmissionelectron microscopy (TEM).

Results: For Clearfil SE Bond,both aging conditions and timehad a significant effect on bondstrengths. Under in vivo condi-tions, the mean mTBS was21.3 MPa at 24 hours but only13.8 MPa at 1 year, a significantdecrease. In vitro, the respectivemeans were 33.9 MPa and21.4 MPa, and the decrease overtime was significant.

For Clearfil Protect Bond, onlyaging conditions—nottime—significantly affected bondstrengths. Bond strengths weregreater under in vitro than underin vivo conditions but did notdecrease with time in either case.In vivo, the 24-hour mean mTBSwas 17.9 MPa and the 1-yearmean was 18.6 MPa. In vitro, therespective means were 28.1 MPaand 28.3 MPa.

TEM showed that bothadhesives formed thin, partiallydemineralized hybrid layersunder both conditions.Nanoleakage could beobserved even at 24 hours.

Conclusions: Bond strengths ofboth self-etch adhesive systemsdecreased over time under in vitroand in vivo conditions. Bondstrengths were lower in vivothan in vitro, but the pattern ofdegradation was similar underboth conditions.

C O M M E N TA RY

This study is particularly interest-ing because it measured bondstrengths achieved not only inthe laboratory but also under clini-cal conditions. Not surprisingly,the results were better in thelaboratory. Numerous clinicalfactors, including but not limitedto dentin fluid movement andfunctional stresses, very likelyhave adverse effects onbonding efficacy.

Some studies have reported thatClearfil SE Bond mediates achemical bond to residualhydroxyapatite in the hybridlayer (see papers by Yoshida andcolleagues as well as Fukegawaand colleagues under “SuggestedReading”), which potentiallycould improve the durability ofresin-dentin bonds. That was notthe case for SE Bond in this par-ticular study, although a similarmaterial (Clearfil Protect Bond)did provide a bond that wasstable at 1 year.

S U G G E S T E D R E A D I N G

Armstrong SR, Vargas M, Fang Q, Laffoon J.Microtensile bond strength of a total-etch3-step, total-etch 2-step, self-etch 2-step,and a self-etch 1-step dentin bondingsystem through 15-month water storage.J Adhes Dent 2003;5:47–56.

Fukegawa D, Hayakawa S, Yoshida Y, et al.Chemical interaction of phosphoric acidester with hydroxyapatite. J Dent Res2006;85:941–4.

Yoshida Y, Nagakane K, Fukuda R, et al.Comparative study on adhesive perfor-mance of functional monomers. J DentRes 2004;83:854–8.

H Y D R O LY T I C S TA B I L I T Y O F S E L F - E T C H A D H E S I V E S B O N D E D T O D E N T I N

S. Inoue, K. Koshiro, Y. Yoshida, J. De Munck, K. Nagakane, K. Suzuki, H. Sano, B. Van MeerbeekJournal of Dental Research (2005;83:1160–4)

A B S T R A C T

Objective: The purpose of thisstudy was to evaluate the hydro-lytic stability of three self-etchadhesive systems containing differ-ent functional monomers.

Materials and Methods: Threetwo-step self-etch adhesive systemswere used in this study—ClearfilMegaBond (Kuraray; marketed asClearfil SE Bond outside Japan,and referred to by the latter

name in this review), Unifil Bond(GC, Tokyo, Japan), and ClearfilLiner Bond II (Kuraray). Theadhesive monomers in thesematerials are, respectively,10-MDP, 4-MET, and phenyl-P.

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Each is a two-step system usinga self-etch primer.

Occlusal enamel was sectionedfrom extracted human thirdmolars to expose mid-coronaldentin, which was polished to600-grit using silicon carbide abra-sive paper to produce standardizedsmear layers. The three adhesiveswere applied according to manu-facturers’ instructions, and Z100(3M ESPE, St. Paul, MN, USA)composite was applied and light-activated in increments. Using awater-cooled diamond saw, eachbonded specimen was sectionedinto small slabs of approximately1 mm cross-sectional area. Speci-mens were untouched (control)or were thermocycled 10,000,20,000, 30,000, 50,000, or100,000 times between 5°C and55°C, with a dwell time of 60seconds in each water bath. Threeteeth were used for each condition(combination of thermocycling andadhesive type).

Microtensile bond strength(mTBS) testing was performedusing a desktop materials tester(EZ-Test, Shimadzu, Kyoto,Japan). Additional specimensof each adhesive (either controlsor thermocycled 100,000 times)were fixed, dehydrated, andembedded in epoxy resin fortransmission electron microscopy(TEM) analysis of resin–dentin interfaces.

Results: For the control groups,mean mTBS values were37.9 MPa for Unifil Bond,40.8 MPa for Clearfil SE Bond,and 44.7 MPa for Liner Bond II.Bond strengths of all three adhe-sives were reduced by thermocy-cling, but the difference was notstatistically significant for SE Bond.Mean bond strengths declined to23.2 MPa for Liner Bond II after100,000 thermocycles and to22.5 MPa for Unifil Bond.However, the mean bond strengthof SE Bond declined only to35.3 MPa. All of the adhesivesproduced shallow hybrid layerscontaining residual hydroxyapatitecrystals, but this was particularlytrue for Clearfil SE Bond. Theinterfacial morphology of hybridlayers formed by SE Bond wassimilar regardless of whether thespecimens had not been ther-mocycled or had been ther-mocycled 100,000 times.

Conclusions: Long-term durabilityof resin–dentin bonds mightdepend on chemical bonding ofthe functional monomer.

C O M M E N TA RY

Penetration of resin-based adhe-sives into etched or conditioneddentin surfaces results in the for-mation of a hybrid layer, whichis called “hybrid” because it is amixture of resin and dentin. Somemild self-etch materials do notcompletely remove hydroxyapatite

crystals from the dentin surface,and evidence suggests that someadhesive monomers might bondchemically with the residualhydroxyapatite. As the presentstudy suggests, such chemicalbonding might improve thedurability of resin-dentin bonds.

S U G G E S T E D R E A D I N G

Casagrande L, de Hipólito V, de Góes MF,et al. Bond strength and failure patternsof adhesive restorations in primary teethaged in the oral environment. Am J Dent2006;19:279–82.

Osorio R, Pisani-Proenca J, Erhardt MC, et al.Resistance of ten contemporary adhesivesto resin-dentine bond degradation. J Dent2008;36:163–9.

Yoshida Y, Nagakane K, Fukuda R, et al.Comparative study on adhesive perfor-mance of functional monomers. J DentRes 2004;83:454–8.

C R I T I C A L A P P R A I S A L

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F I V E - Y E A R C L I N I C A L E F F E C T I V E N E S S O F A T W O - S T E P S E L F - E T C H I N G A D H E S I V E

M. Peumans, J. De Munck, K. Van Landuyt, P. Lambrechts, B. Van MeerbeekJournal of Adhesive Dentistry (2007;9:7–10)

A B S T R A C T

Objective: This study was designedto evaluate the clinical perfor-mance of Clearfil SE Bond in resto-ration of Class V lesions.

Materials and Methods: Twenty-nine patients received two or fourrestorations of non-carious cervicallesions; the total number of resto-rations was 100. Clearfil SE Bond,which is a mildly acidic self-etchprimer system, was used accordingto manufacturer’s directions forhalf of the restorations. For theothers, enamel was selectivelyetched using 40% phosphoric acidbefore the adhesive system wasapplied. The same composite resinmaterial was used for all restora-tions. Tooth preparation involvedroughening of the dentin surfaceswith a coarse diamond and place-ment of a 1–2 mm bevel onenamel margins.

The restorations were evaluatedafter 6 months, and 1, 2, 3, and5 years of clinical service. Therecall rate was 84% at 5 years.Two evaluators rated eachrestoration using a standard setof criteria for retention, marginalintegrity, marginal discoloration,recurrent caries, post-operativesensitivity, and preservation oftooth vitality.

Results: At 5 years, only one resto-ration had been lost from thegroup of restorations placed usingmanufacturer’s directions, andnone were lost from the selectiveetching group. In both groups,marginal integrity deteriorated overtime. However, the deteriorationwas worse for the no-etch group,in which significantly more enamelmargin defects were detected.Marginal discoloration was morefrequent in the no-etch group. Norecurrent caries, post-operativesensitivity, or loss of vitalitywas observed.

Conclusions: Marginal defectsin the no-etch group were clini-cally acceptable and did notrequire any repair, indicatingthat the bonding effectivenessof Clearfil SE Bond remainedrelatively good despite thematerial’s superficial interactionwith enamel. Selective enameletching improved marginaladaptation but did not affectthe overall clinical performanceof Class V restorations.

C O M M E N TA RY

Although laboratory testing canbe very useful for studying variousaspects of adhesive performanceand screening new materialsduring product development,

the best evidence for efficacy ofresin-based adhesives is found incontrolled clinical trials. Thisparticular study was a relativelylong-term (5 years) clinical trialof the most popular self-etchprimer system, Clearfil SE Bond.It was a typical clinical trialinvolving restoration of non-carious cervical lesions.

Clearfil SE Bond is known to beonly mildly acidic, so one of theprimary objectives of the study wasto determine the durability of itsenamel bond and whether selectiveacid-etching might improve dura-bility. The authors concluded thatthe overall performance of theClass V restorations was similarin both groups. However, marginalintegrity was better, and marginaldiscoloration was less frequentwhen enamel margins wereetched before the adhesivesystem was applied.

Selective etching of enamel,therefore, is an acceptable tech-nique for self-etch primer systemswhen the operator is concernedabout enamel marginal integrity.Contact of the acid etchant withdentin should be avoided asmuch as possible because itcan reduce adhesion of self-etchprimers to dentin.

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S U G G E S T E D R E A D I N G

Pashley DH, Tay FR. Aggressiveness of con-temporary self-etching adhesives. Part II:etching effects on unground enamel.Dent Mater 2001;17:430–44.

Peumans M, Kanumilli P, De Munck J, et al.Clinical effectiveness of contemporary

adhesives: a systematic review of currentclinical trials. Dent Mater 2005;21:864–81.

Soares CJ, Castro CG, Santos Filho PC, daMota AS. Effect of previous treatments onbond strength of two self-etching adhesivesystems to dental substrate. J Adhes Dent2007;9:291–6.

Van Landuyt KL, Kanumilli P, De Munck J,et al. Bond strength of a mild self-etchadhesive with and without prior acid-etching. J Dent 2006;34:77–85.

F O U R - Y E A R WAT E R D E G R A D AT I O N O F A T O TA L - E T C H A N D T W O S E L F - E T C H I N G A D H E S I V E SB O N D E D T O D E N T I N

A.I. Abdalla, A.J. FeilzerJournal of Dentistry (2008;36:611–7)

A B S T R A C T

Objective: The purpose of thisstudy was to evaluate the effect ofdirect and indirect water storageon the microtensile dentin bondstrength (mTBS) of one etch-&-rinse and two self-etch adhesives.

Materials and Methods: The mate-rials used in this study were theone-bottle etch-&-rinse systemAdmira Bond (Voco, Cuxhaven,Germany), the self-etch primersystem Clearfil SE Bond, and theall-in-one self-etch adhesive HybridBond (Sun Medical, Shiga, Japan).Standardized Class I cavity prepa-rations were made in the occlusalsurfaces of 54 extracted humanmandibular molars. The prepara-tions extended approximately1 mm into dentin and had allmargins in enamel. The enamelmargins were beveled.

The prepared teeth were dividedinto groups of 18, and the prepara-tions were restored with composite

resin following application of theadhesives according to manufactur-ers’ directions. The restored teethin each group were divided intothree sub-groups based on time ofstorage in water. The storage timeswere 24 hours and 4 years. For the24-hour group and one of the4-year groups, the specimens weresectioned for mTBS after storage inwater. In the other 4-year group,specimens were sectioned beforestorage in water. Thus, in this lastgroup, resin–dentin interfaces wereexposed directly to water. Thebond strength test was done usinga universal testing machine.

Results: At 24 hours, the meanmTBS were 39 MPa for AdmiraBond, 41 MPa for Clearfil SEBond, and 37 MPa for HybridBond. After 4 years without directexposure of the resin–dentin inter-faces to water, mean bondstrengths had declined verylittle—the worst being a reductionof 5 MPa for Hybrid Bond.

However, after four years of directexposure to water, the bondstrengths of all three adhesiveswere significantly lower—22 MPafor Admira Bond, 21 MPa forClearfil SE Bond, and 12 MPa forHybrid Bond.

Conclusions: Exposure to watercauses deterioration of resin bondsto dentin. In restorations withmargins in enamel, etching theenamel could protect the bondfrom this effect. However, whenrestoration margins extend intodentin or cementum, bonds arelikely to degrade over time.

C O M M E N TA RY

Laboratory studies on resin–dentinbond longevity tend to reach thesame conclusion as this one—thatis, when resin–dentin bonds aredirectly exposed to water, theydeteriorate over time. In contrast,when the resin–dentin interface isprotected by a bonded resin–enamel interface, degradation ismuch slower. This is an important

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consideration for Class II posteriorcomposites, where the gingivalenamel is frequently lacking inquantity or quality.

The authors state in their conclu-sions that etching enamel marginscan protect resin–dentin bonds,presumably implying that phospho-ric acid-etching is required.However, their own results indicatethat the enamel bond is important

regardless of how it is achieved.Two of the three adhesives testedin this study did not use a separateacid-etching step and yet hadstable dentin bonds when theenamel was present during storage.

Clearfil SE Bond did not performas well in this study as it did in thestudy by Inoue and colleaguesreviewed earlier. Another notewor-thy, and perhaps unsurprising,

finding is that the simplest adhe-sive was the one most affected byexposure to water.

S U G G E S T E D R E A D I N G

DeMunck J, Van Landuyt K, Peumans M,et al. A critical review of the durability ofadhesion to tooth tissue: methods andresults. J Dent Res 2005;84:118–32.

De Munck J, Shirai K, Yoshida Y, et al. Effectof water storage on the bonding effective-ness of 6 adhesives to Class I cavitydentin. Oper Dent 2006;30:456–65.

T H E B O T T O M L I N E

• Much of the research on self-etch primer systems has focused on one commercial product, Kuraray’sClearfil SE Bond.

• Mildly acidic self-etch primers such as Clearfil SE Bond form partially demineralized hybrid layerscontaining residual hydroxyapatite crystals. Because of this, there is potential for chemical interactionbetween adhesive monomers and hydroxyapatite that could improve the durability ofresin–dentin bonds.

• Clinical trials have reported good results for self-etch primer systems.• At least anecdotally, post-operative sensitivity occurs less frequently with self-etch primer systems than

with etch-&-rinse systems.• The bond of mildly-acidic self-etch primers to enamel can be improved by selective etching of the

enamel before primer application. Contact of the etchant with dentin should be avoided as muchas possible.

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