Bonding Efficacy and Fracture Pattern of Adhesives Submitted to Mechanical Aging with the Rub&Roll Device.

PURPOSE To evaluate the effect of water storage and cyclic loading on the microtensile bond strength (μTBS) and fracture pattern of adhesives to dentin. MATERIALS AND METHODS Midcoronal dentin surfaces (n = 36) were prepared and composite restorations were built up using two adhesives (self-etch and etch-and-rinse). The specimens were randomly divided into 3 groups according to the aging conditions (n = 6): 1. CONTROL storage in water for 24 h (CO); 2. water storage: storage in water for 6 months (WS); 3. mechanical loading: 750,000 mechanical cycles (ML) using the Rub&Roll loading device. Specimens were sections into beams and the μTBS was tested. Fracture patterns were analyzed using stereomicroscopy and fractographic analysis was performed using SEM. μTBS data (n = 53-72 specimens) were subjected to two-way ANOVA and Tukey's post-hoc test. The chi-squared test was used to compare the distribution of failure modes (p < 0.05). RESULTS Aging conditions and adhesives significantly affected μTBS (p < 0.01). The CO group showed no difference between materials and had highest μTBS. After WS, the self-etch adhesive showed higher μTBS than did the etchand- rinse adhesive. ML resulted in lower μTBS for both adhesives. Materials (p < 0.01) and aging (p < 0.01) significantly influenced the distribution of failure modes. SEM analysis showed that specimens submitted to WS or ML showed features of degradation and fatigue at the fractured interface, depending on the adhesive. CONCLUSION Mechanical loading had a negative effect on the bonding efficacy of both adhesives and influenced the fracture pattern, with specimens presenting a different fracture surface from that observed in water-stored specimens.