Immediate and 6-month bond strengths of different adhesives in the oral environment

Purpose: To evaluate the microtensile bond strength (μTBS) of three adhesives to dentin after 1 week and 6 months in an oral environment. Materials and Methods: Class I cavities were prepared in the third molars of 30 patients and randomized into 3 groups according to the following adhesives: Scotchbond Multi-Purpose (SM), Clearfil Protect Bond (CF), and Scotchbond Universal (UN). These molars were then subdivided into two groups according to the exposure time in the oral environment: one week (1W) and 6 months (6M). After the exposure time, the teeth were extracted, cut into beams, and submitted to the μTBS test. The data were analyzed using the Shapiro-Wilk test and two-way ANOVA followed by Tukey's post-hoc test with a significance level of 5%, and fracture modes were analyzed. Results: The bond strengths in MPa (mean ± SD) were SM-1W: 39.5 ± 7.9; SM-6M: 29.7 ± 1.8; CF-1W: 30.5 ± 1.4; CF-6M: 28.6 ± 4.1; UN-1W: 30.6 ± 3.2; and UN-6M: 26.7 ± 2.0. The SM-1W group exhibited significantly increased μTBS compared with the other groups. After 6 months in the oral environment, a significant reduction of μTBS was only observed for the SM group, whereas similar bond strengths were observed for the other groups. SM-1W exhibited a predominance of mixed fractures, whereas the other groups showed a predominance of adhesive fractures. Conclusions: The adhesives which were applied in the self-etching mode maintained bond strength after six months in the oral environment. A reduction of μTBS was only observed for the three-step etch-and-rinse adhesive.