Effect of bleaching treatment and reduced application time of an antioxidant on bond strength to bleached enamel and subjacent dentin.

PURPOSE: To evaluate the influence of bleaching on bond strength to enamel and subjacent dentin, and to determine whether a reduced application time (1 min) of the antioxidizing agent can obviate the compromised bond strength after bleaching. MATERIALS AND METHODS: One hundred twelve bovine incisors were obtained, and the enamel and dentin surfaces were standardized to a thickness of 1 mm. The specimens were divided into two control groups (enamel and dentin without treatment) and 12 experimental groups (n = 10), based on the concentration of bleaching agents (carbamide peroxide 16% and hydrogen peroxide 35%), time interval between bleaching and restorative procedures (24 h; 24 h + sodium ascorbate (SA) 10%/1 min; 14 days), and substrate (enamel or dentin). All samples were submitted to the bleaching treatment on enamel. After the stipulated interval, a microshear test was performed. RESULTS: The bleaching treatment compromised the bond strength to the enamel when the restoration was performed 24 h after the end of bleaching. The bond strength to dentin was not affected by bleaching. CONCLUSIONS: The SA 10% application for 1 min obviates the detrimental effect of bleaching on bond strength. The bleaching performed on enamel does not affect the bond strength to the subjacent dentin.

Effect of the diffusion of bleaching agents through enamel on dentin bonding at different depths.

PURPOSE: To evaluate the influence of two concentrations of bleaching agents applied over enamel surfaces on the dentin bonding at different depths. METHODS: Twenty-four bovine incisors were sectioned, obtaining three fragments per tooth (4x4 mm). Each fragment presented a 0.7 mm enamel thickness; and the dentin thickness varied according to the experimental group: 0.5 mm, 1 mm or 1.5 mm. Fragments from each dentin-thickness were allocated into three groups (n=8): G1: Control (no bleaching); G2: 16% carbamide peroxide (6 hours/14 days); G3: 35% hydrogen peroxide (three 15-minute treatments). 24 hours after enamel bleaching, the adhesive system was applied and dentin surfaces were restored with resin composite cylinders (2 mm diameter and 1 mm height). The micro-shear testing was performed immediately after restorative procedures, at a speed of 0.5 mm/minute until failure. Bond strength values, in MPa, were statistically analyzed (split-plot ANOVA/Tukey alpha=0.05). RESULTS: Means obtained were: G1-0.5 mm: 13.5, G1-1 mm: 9.48, G1-1.5 mm: 9.01; G2-0.5 mm: 9.64, G2-1 mm: 9.44, G2-1.5 mm: 9.27; G3-0.5 mm: 11.68, G3-1 mm: 11.64, G3-1.5 mm: 7.63. Regardless of the dentin thickness, bleached groups presented bond strengths similar to that of control groups. Nevertheless, significant differences among dentin depths were detected (P=0.02); and the lowest bond strength was observed on the deepest dentin (1.5 mm). The diffusion of bleaching agents through enamel surfaces did not affect the bond strength to dentin, which is highly dependent on the morphology/depth of the substrate.