Prime-and-rinse Approach For Improving The Enamel Micro-tensile Bond Strengths Of Self-etch Adhesives

Objectives:The study investigated the effects of prime-and-rinse approach using 15%MDP(10-methacryloyloxydecyl dihydrogen phosphate)-containing primer on the enamel micro-tensile bond strengths(MTBS)of(ultra-)mild self-etch adhesives,enamel surfaces and enamel-resin interfaces.Materials and Methods:Sixty-nine human third molars were polished with 320-grit SiC paper under water running to create a uniform smear layer.Sixty teeth were randomly assigned to three groups according to different enamel pre-treatments(application approaches):1.Control group(self-etch approach):The enamel surfaces were not further treated serving as control;2.(Selective)enamel etching approach:The enamel surfaces were etched with 37%phosphoric acid for 15 s,water-sprayed for 30 s and gently dried;3.Prime-and-rinse approach:The enamel surfaces were primed with 15%of MDP primer,water-sprayed for 30 s and gently dried.Four mild one-step self-etch adhesives and the respective composite resins from the same manufacturers(Adper Easy One + Filtek Z350(3M ESPE);Clearfil S3 Bond + Clearfil Majesty(Kuraray-Noritake Co.);G Bond(GB)+ Gradia Direct(GC Gradia Direct Japan);iBond(IB)+ Charisma(Charisma Heraeus Kulzer))were applied onto the enamel surfaces.The specimens were stored in the distilled water in 37? for 24 h.Then forty-eight specimens(4 teeth per subgroup)were selected and prepared for micro-tensile bond strength(MTBS)test.After the MTBS tests,the modes of failure were determined by stereomicroscopy(OLYMPUS,SZ61,Japan)at a magnification of 50-fold and two de-bonded specimen from each subgroup were randomly selected for SEM observation.Another 12 specimens(1 teeth per subgroup)were prepared for transmission electron microscopy(TEM)observations.The other 9 teeth were prepared as the above-mentioned without adhesives and composite resin placement and to be used for SEM observation.Statistical analysis was performed with the SPSS 22.0 software(IBM SPSS Statistics ver.22.0,IBM Corp.New York,USA).Statistical analysis was performed using the Kruskal-Wallis test followed by post-hoc pairwise comparisons with Bonferroni correction to analyze all the MTBS data.Chi-square(X2)test was used to compare the failure modes of the different enamel pre-treatment approaches of the four adhesives.Results:In the control group(self-etch approach),there was no significant difference of the enamel MTBS among the four adhesives(P>0.05).Compared with the control,enamel etching approach and prime-and-rinse approach could significantly increase the enamel MTBS(P<0.01),regardless of the adhesives evaluated.However,there were no significant differences of enamel MTBS between(selective)enamel etching approach and prime-and-rinse approach(P>0.05).Most of the failure modes were the mixed failure in this study(P<0.001)except for adhesive Cleafil S3 Bond using prime-and-rinse approach.There were no significant differences of the failure modes between(selective)enamel etching approach and prime-and-rinse approach(P>0.05).Overall,self-etch approach produced more adhesive failures than(selective)enamel etching approach and prime-and-rinse approach(P<0.01).The SEM findings showed that the acid-etched enamel surface revealed a distinct etching pattern with exposure of enamel prism rods.The enamel smear layer was nearly completely removed in the exposure of the enamel HAp crystallites,and some irregular patches of insoluble MDP-Ca salts scatteredly remained on the enamel surface.The TEM findings revealed that enamel smear layer still could be detected at the enamel-adhesive interface in control group,while could not found in the(selective)enamel etching approach and prime-and-rinse approach.Conclusions:The prime-and-rinse approach using MDP-containing primer prior to the application of mild self-etch adhesives could significantly increase the enamel MTBS,which equaled to those of(selective)enamel etching approach.Hence,the innovative prime-and-rinse approach might be used as an supplement to contemporary dental bonding strategies.