Prolonged exposure times of one-step self-etch adhesives on adhesive properties and durability of dentine bonds

Objectives: To evaluate the effect of prolonged exposure times on immediate and 6-month adhesive properties: degree of conversion (DC), nanoleakage (NL) and resin-dentine bond strength (mu TBS) of three one-step self-etch adhesive systems (Adper Easy One [EO], Clearfil S-3 Bond [CS3] and Go [GO]). Material and methods: The adhesives were applied on exposed dentine surfaces of 90 human molars according to manufacturers' instructions and light polymerized for 10, 20, and 40 s at 600 mW/cm(2). Bonded teeth were sectioned to obtain stick-shaped specimens (0.8 mm(2)) and tested under tensile stress (0.5 mm/min) immediately (IM) or after 6 months of water storage. Two bonded sticks from each tooth at each storage time interval were analysed by SEM for NL evaluation. The in situ DC was evaluated by micro-Raman spectroscopy. Data were analysed by appropriate ANOVA and Tukey's test (alpha = 0.05). Results: Prolonged exposure times significantly increased the DC (%) (10 s [67.4 +/- 17.3]; 20 s [85.9 +/- 8.9] and 40 s [85.2 +/- 9.0]) and decreased the NL (%) (10 s [24.8 +/- 13.2]; 20 s [13.3 +/- 7.5] and 40 s [13.5 +/- 9.3]) for all adhesives; however it did not increase the IM mu TBS for two (EO, GO) out of the three adhesives. Furthermore, this technique did not minimize dentine bond degradation. Conclusion: Although longer exposure times than those recommended could not prevent degradation of dentine bonds, they could increase DC within the hybrid layer and reduced NL for all adhesives tested. (C) 2012 Elsevier Ltd. All rights reserved.