Effects of Alpha-Tocopherol Antioxidant on the Bonding Properties of Resin Adhesive to Dentin Bleached with Sodium Perborate

Abstract

Previous reports have shown diminished capacity for bonding after bleaching teeth. Reversal of the bond strengths back to pre-bleached levels can be obtained with application of 10% alpha-tocopherol in a 2-hour time frame, or by delaying bonding for two weeks. This study evaluated the effectiveness of a 5-minute application of 20% alpha-tocopherol to reverse the deleterious effect of nonvital bleaching on dentin bonding. Thirty third molars were prepared to obtain a flat dentin surface and assigned to three groups: unbleached, bleached, and bleached followed by 5-minute treatment with 20% alpha-tocopherol. The dentin surfaces of the bleached groups were exposed to sodium perborate (2 g/mL) for seven days. The post-bleach treatment group was subsequently treated with 20% alpha tocopherol for 5 minutes, then all groups were restored with restorative composite. After 24 hour storage at 37oC and 100% humidity, restored tooth specimens were sectioned into 1 mm2 dentin-composite beams. Four to six beams from each tooth were subjected to microtensile bond strength testing. Following microtensile testing, 2 beams from representative specimens were further evaluated with Raman microspectroscopy for depth of penetration and degree of conversion of adhesive resin. Mean bond strength values (MPa) for each group: unbleached control=26.2, bleached control=20.3, post-bleach treatment group=18.5. A 1-factor ANOVA and Tukey post hoc test (α=0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term alpha-tocopherol treatments did not improve post-bleach bond strength. While Raman microspectroscopy revealed depth of penetration and degree of conversion for the post-bleach alpha-tocopherol group were similar to the bleached control, both values were markedly lower than the unbleached control group. Collectively, the results suggest that the application of 20% alpha-tocopherol as a post-bleach treatment in a clinically relevant time frame was not effective in counteracting the deleterious effect of bleaching on bond strength, and composite resin bonding procedures should be delayed following tooth bleaching.