Effects of Alpha-Tocopherol Antioxidant on the Bonding Properties of Resin Adhesive to Dentin Bleached with Sodium Perborate
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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.
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Introduction -- Materials and methods -- Results -- Discussion -- Conclusions
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M.S.