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 (µTBS) 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 (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.

Ultrastructural evaluation of enamel after dental bleaching associated with fluoride.

This study evaluated the effects on human enamel after two bleaching procedures: with a fluoridated bleaching agent and with topical fluoride application postbleaching. It used 43 enamel blocks (3 mm(2) ) that were ground flat (600-2,000 grit) and polished with polishing paste (one and one-fourth). Specimens were randomly divided into three groups according to the bleaching procedure: (1) control group, (2) hydrogen peroxide 35% (HPF) and topical application of fluoride 1.23%, and (3) HP 38% (OP) with fluoride in its composition. Bleaching agents were used according to the manufacturer's instructions. Three methodologies were used: nanoindentation, to observe surface hardness and elastic modulus; atomic force microscopy, to observe surface roughness (R(a) - R(z)); and scanning electron microscopy, to observe the enamel surface effects. Group OP had a decrease in the elastic modulus after bleaching, which was recovered at 14 days. An increased roughness (R(a); 32%) was observed on group HPF and had an increased erosion on enamel surface (67%). It was concluded that topical application of fluoride, after using the nonfluoridated whitening agent, increased the roughness values and erosion of enamel.