Effect of dentinal surface preparation on bond strength of self-etching adhesives

Purpose: This study examined the effects of cutting dentin with different burs at various speeds on the microtensile bond strength (μTBS) of two self-etching adhesive systems. Materials and Methods: Flat deep dentin surfaces from 50 extracted human third molars were divided into 5 groups (n = 10) according to bur type and speed of rotation: (I) high-speed diamond bur, (II) low-speed diamond bur, (III) high-speed tungsten carbide bur, (IV) low-speed tungsten carbide bur. Controls were abraded with 600-grit SiC paper. A two-step self-etching adhesive, Clearfil SE Bond (SE, Kuraray) and a one-step self-etching adhesive, Clearfil S³ Bond (S³, Kuraray) were applied to dentin surfaces and light cured. Composite buildups were performed using Filtek Z250 (3M ESPE). For μTBS evaluation, composite-dentin beams of 0.8 mm² were stressed to failure at a crosshead speed of 1 mm/min. The μTBS data were analyzed using two-way ANOVA and Tukey's multiple comparison tests. Representative fractured beams from each group were prepared for fractographic analysis under SEM. Results: Two-way ANOVA showed that the effects of dentin surface preparations, adhesive systems, and their interaction were statistically significant (p < 0.001). The μTBS was the highest when bonding SE to dentin surface prepared with 600-grit SiC abrasive paper (47.3 ± 7.4 MPa), followed by high-speed tungsten carbide burs (40.8 ± 6.1 MPa), and the lowest when bonding S³ to dentin surfaces prepared with a high-speed diamond bur (15.2 ± 6.2 MPa). SEM observation of the fractured surfaces revealed mixed and adhesive failures for SE groups, while in the S³ groups, adhesive failures predominated with numerous inclusion droplets. Conclusion: Higher bond strengths are achieved with SE bond when applied on dentin surfaces prepared with tungsten carbide burs. Proper bur and adhesive selection are essential to optimize dentin adhesion of self-etching adhesives.