Influence of a hydrophobic resin coating on the bonding efficacy of three universal adhesives

Objectives To evaluate the effect of an additional hydrophobic resin coating (HE) on the resin-dentine microtensile bond strengths (μTBS), nanoleakage (NL), and in situ degree of conversion (DC) of three universal adhesives used in the etch-and-rinse (ER) and the self-etch (SE) modes. Methods Sixty caries-free extracted third molars were divided into 12 groups according to the combination of the factors adhesive (All-Bond Universal [ABU]; G-Bond Plus [GBP] and Scotchbond Universal [SBU]), adhesive strategy (ER and SE), and the use of HE (Heliobond; yes or no). After restorations were constructed, specimens were stored in water (37 °C/24 h) and sectioned into resin-dentine beams (0.8 mm²) to be tested under tension (0.5 mm/min). Selected beams from each tooth were used for DC quantification and for NL evaluation. Data from each adhesive were analyzed with two-way ANOVA and Tukey's test (α = 0.05). Results ABU and GBP resulted in higher μTBS in the ER mode. The use of HE increased the μTBS of ABU and GBP only in the SE mode. Lower NL was observed for SBU and ABU in the ER mode + HE, and for GBP in the SE mode + HE. SBU and GBP showed higher DC when used in the ER mode, which was increased with HE application. The DC of ABU was similar in all conditions. Conclusions The conversion of 1-step SE to 2-step SE may increase the μTBS and DC of current universal adhesives. The reduction in the NL is more dependent on the adhesive composition than on the bonding strategy.