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

Abstract:

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 (μTBS) of three one-step self-etch adhesive systems (Adper Easy One [EO], Clearfil S3 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/cm2. Bonded teeth were sectioned to obtain stick-shaped specimens (0.8 mm2) 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 (α = 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 μTBS 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. © 2012 Elsevier Ltd All rights reserved.