Effect of Sodium Ascorbate or Alpha-Tocopherol on the Resin-Dentin Interface and Bond Strength after Endodontic Treatment and Bleaching

The objective of this in vitro study was to assess the effects of two antioxidants (sodium ascorbate [SA] and alpha-tocopherol [AT]) on the adhesive interface and dentin bond strength immediately after bleaching with 38 % hydrogen peroxide (38HP) in endodontically-treated teeth. Two stages of experimentation were carried out. Bovine incisors were allocated into four groups (n = 10/group for each experiment): NB, non-bleached restored crowns; 38HP, bleached and immediately restored crowns; 38HP-SA, bleached crowns and SA use; and 38HP-AT, bleached crowns and AT use. Hybrid layer length in dentin (μm) and bond strength (MPa) were assessed with confocal microscopy laser and micro-shear bond strength (μSBS) test, respectively. Failure mode was determined by stereomicroscope. Data analysis was performed with analysis of variance (ANOVA) and Kruskal-Wallis, Dunn, Tukey, and Fisher-exact tests (a = 0.05). Higher values of hybrid layer length were observed similarly in the NB and 38HP-SA groups. The highest μSBS mean values were observed in the NB group (18 .51 ? 1.33), whereas the SBS values for 38HP-AT (1.68 ? 0.32) were similar to the 38HP group (1.61 ? 0.51) (p > 0.05) and significantly lower than the 38HP-SA group (5.78 ? 0.71). Adhesive failures were predominant in the 38HP and 38HP-AT groups. Cohesive and mixed failures were mostly observed in the NB and 38HP-SA groups, respectively. In conclusion, AT has no immediate effect on the hybrid layer formation and μSBS of dentin. Although SA promotes an increase in hybrid layer formation, it was not reflected in the μSBS values.