Effect of double-application of all-in-one adhesives on dentin bonding

Objectives To evaluate the effect of double-application of all-in-one adhesives using the micro-shear bond test. Methods The occlusal surfaces of extracted human third molars were ground perpendicular to the long axis of each tooth to expose a flat dentin surface. Three commercially available and one experimental bonding system were used in this study: Adper Prompt L-Pop (APL, 3M ESPE), REACTMER BOND (RB, Shofu), XENO III (Xeno, Dentsply-Sankin) and newly developed OBF-2 (OB2, Tokuyama Dental). These adhesives were applied on the dentin surfaces by either the manufacturersʹ instructions or by an experimental method (single-application or double-application). Resin composite was then placed and light-cured for 40 s. After 24 h immersion in water, a micro-shear bond test was carried out and the fractured dentin surfaces were observed microscopically. The data were analyzed by one-way ANOVA and Tukeyʹs HSD tests (p<0.05). Results The mean bond strengths of APL, RB, Xeno and OB2 with single-application were 22.7, 28.3, 30.3 and 34.6 MPa, respectively. The mean bond strengths of APL, RB, Xeno and OB2 with double-application were 29.5, 27.2, 29.6 and 32.5 MPa, respectively. There were no statistically significant differences in micro-shear bond strengths between the single- and double-application methods for each adhesive system (p>0.05). The morphological observation of the fractured dentin surfaces revealed differences between the single- and double-application groups especially for APL and OB2. Conclusions Micro-shear bond strengths of all-in-one adhesives in this study showed no statistically significant differences between the single-application and the double-application method.