Aim: To evaluate the effect of two antioxidant formulations (sodium ascorbate and α-tocopherol) on fracture resistance of endodontically treated teeth.

Materials and methods: Sixty human premolars were endodontically treated and divided into six groups (n = 10): G1 (negative control)-unbleached and restored with composite resin; G2 (positive control)-bleached in three sessions, using hydrogen peroxide (15 H₂O₂) plus titanium dioxide (TiO₂) nanoparticles, photoactivated by LED laser system and restored with composite resin; G3-bleaching similar to G2, after the use of 10% sodium ascorbate gel for 24 hours and restored with composite resin; G4-similar to G3, but with the use of 10% sodium ascorbate solution and restored with composite resin; G5 and G6-similar to G3, but with the use of 10% α-tocopherol in alcohol or carbopol, respectively, and was also restored. A mechanical fracture resistance test was performed and the Kruskal-Wallis test was used to evaluate the results (α = 0.05).

Results: No statistical difference was observed in fracture resistance between groups (p > 0.05). Regarding the antioxidant and pharmaceutical formulation applied, no statistical difference was detected in any comparison (p > 0.05). The frequency of fractures considered favorable was higher in G1 and G3 compared to the other groups.

Conclusion: The endodontically treated teeth bleached with 15 H₂O₂ plus TiO₂ nanoparticles and photoactivated with the LED laser did not decrease the fracture resistance and the use of sodium ascorbate or α-tocopherol did not increase the crown fracture resistance.

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