Tensile bond strength of brackets after antioxidant treatment on bleached teeth.

Various studies have reported a significant reduction in tensile bond strength of brackets when bonding is carried out immediately after bleaching. The purpose of this investigation was to determine the effect of an antioxidant agent on the tensile bond strength values of metal brackets bonded with composite resin to human enamel after bleaching with carbamide peroxide (CP). A total of 80 extracted premolar teeth were randomly divided into three bleaching groups of 10 per cent CP and an unbleached control group. The specimens in group 1 were bonded immediately after bleaching; group 2 were stored in an artificial saliva solution for 7 days after bleaching; group 3 were treated with 10 per cent sodium ascorbate, immediately before bonding, whereas the unbleached specimens in group 4 had no treatment before bonding. Tensile bond strengths were established in MPa. To evaluate the amount of resin left on the enamel surfaces after debonding, the adhesive remnant index (ARI) scores were used. The tensile bond strength data were analyzed with the Kruskal-Wallis test and pairwise comparisons were made by the Mann-Whitney U test at a significance level of P < 0.05. The brackets bonded immediately after bleaching revealed significantly lower tensile bond strengths than those of unbleached enamel (P = 0.000). No statistically significant differences in tensile bond strength were noted when the delayed-bonding (P = 6.000) and antioxidant-treated (P = 0.2757) groups were compared with the control group. The antioxidant treatment immediately after bleaching was effective in reversing the tensile bond strength of brackets.

Effect of 10% sodium ascorbate on the shear bond strength of composite resin to bleached bovine enamel.

The purpose of this study was to comparatively investigate the effect of antioxidant treatment and delayed bonding after bleaching with three different concentrations of carbamide peroxide (CP) on the shear bond strength of composite resin to enamel. One hundred flat buccal enamel surfaces obtained from bovine incisors were divided into three bleaching groups of 10, 16 and 22% CP (n = 30) and a control group. Each bleaching group was then divided into three subgroups (n = 10). Group 1 consisted of specimens bonded immediately after bleaching. Group 2 specimens were treated with antioxidant agent, 10% sodium ascorbate, while Group 3 specimens were immersed in artificial saliva for 1 week after bleaching. Specimens in the control group were not bleached. After the specimens were bonded with Clearfil SE Bond and Clearfil AP-X, they were thermocycled and tested in shear until failure. Fracture analysis of the bonded enamel surface was performed using scanning electron microscope. The shear bond strength data was subjected to one-way analysis of variance followed by Duncan's multiple range test at a significance level of P < 0.05. Shear bond strength of composite resin to enamel that was bonded immediately after bleaching with 10, 16 and 22% CP was significantly lower than that of unbleached enamel (P < 0.05). For all three bleaching groups, when the antioxidant-treated and delayed bonding (1 week) subgroups were compared with the control group, no statistically significant differences in shear bond strength were noted (P < 0.05).