Influence Of Priming Time And Primer’s Concentrations On Bovine Enamel Bond Strengths

Objectives:This study investigated the effects of different priming time and primer’s concentrations on bovine enamel micro-tensile bond strengths (uTBS) using a novel prime-and-rinse approach, and analyzed the enamel μTBS produced by chemical bonding of a neutral primer (5%(w/w) of10-MDP-Na).Methods:The labial enamel surfaces of84non-carious bovine incisors were highly-polished. They were applied with experimental primers containing with different concentrations of10-MDP (10-methacryloxydecyl dihydrogen phosphate)(0.5,1,5,10,20%(w/w)) or neutral primers (5%(w/w) of10-MDP-Na, Kuarary, Co. Japan, or5%EDTA disodium salt (5%EDTA-2Na)) for5,30or60s, before they were thoroughly water-sprayed and totally dried. Half of them were applied with a conventional adhesive Durafill Bond (Heraeus, Germany), gently air-dried, and light-cured for20s according to the manufacturer’s instruction. Two2-mm increments of a composite resin (Bisco, USA) were placed, and light-cured for40s, respectively. After water storage at37℃for24h, the specimens were prepared into sticks of about1×1×8mm through the enamel-resin interface with a low-speed saw (Isomet1000, Buehler, USA). The micro-tensile bond strength (μTBS) tests were performed with a Micro Tensile Tester (Bisco, USA). Another half incisors were treated with the experimental primers as above-mentioned, but neither applied with adhesive, nor placed with composite. This enamel surfaces were then rinsed with acetone and distilled water, dehydrated in a series of ethanol solutions and gold-sputtered, before they were analyzed the pre-treated enamel surface morphology by SEM. The data were analyzed using factorial design ANOVA and post hoc Tukey’s LSD multiple comparisons.Results:There was a significant influence of primer’s concentrations and priming time on bovine enamel μTBS when10-MDP-containing primers used (p<0.001), revealing the optimal priming time (30s) and the best combination (application of the primer containing20%of10-MDP for30s). The enamel treated with the neutral primer (5%10-MDP-Na) did not significantly change the highly-polished enamel surface morphology but produced moderate enamel μTBS, suggesting that chemical bonding of10-MDP to the highly-polished enamel could yield detectable enamel bond strengths. The enamel treated with5%EDTA-2Na solution revealed a loose smear layer with irregular pittings, and nearly all specimens fractured before pre-testing. Mixed failure predominantly occurred in all groups except for0.5%of10-MDP for5. Cohesive failure within enamel and resin composite occasionally took place in some groups.Conclusion:Within the limitations of this in vitro study, it can be concluded that the priming time and different primer’s concentrations (10-MDP) would significantly influence the enamel bond strengths using a novel prime-and-rinse approach. The optimal priming time is30s, and the best combination is an application of a primer containing20%of10-MDP for30s. The prime-and-rinse approach might be an innovative supplement to contemporary dental adhesive approaches. This study, for the first time, demonstrated that chemical bonding of10-MDP-Na on the smooth enamel surface could produce moderate enamel bond strengths.