After the coronal access and root canal preparation with 2.5% sodium hypochlorite and ProTaper System, until the F2 instrument, the canals will be filled with AH Plus cement and gutta-percha by single cone technique. In sequence, after cleaning the pulp chamber with ethanol, the teeth will be divided into six experimental groups (n = 10). In G1 (control), the crowns will be immediately restored with composite resin. In the other groups, teeth are subjected to 3 sessions of intracoronal bleaching, at intervals of 7 days, using 15% hydrogen peroxide (H2O2) with nanoparticles of titanium dioxide, photoactivated with LED-laser. In each session, there will be two applications of photoactivation of the bleaching agent, both on the buccal surface and inside of the pulp chamber. The teeth of G2, after completion of bleaching, will be restored identically to the G1. In the other groups will be kept for 24 hours, an antioxidant with a specific vehicle within the pulp chamber: G3 - 10% sodium ascorbate in natrosol gel; G4 - 10% sodium ascorbate to 10% in aqueous solution; G5 - 10% alpha-tocopherol in alcohol or group 6 - 10% alpha-tocopherol in carbopol. After this period, the agents will be removed, cleaned and the crowns restored with composite resin, similar to the G1. Between sessions of the experiment, the specimens remain immersed in artificial saliva and the pulp chamber filled with gutta-percha and sealed with temporary restorative material. After conclusion of bleaching, a new immersion for 24 additional hours will be held and dental crowns submitted to fracture resistance test, using a device with one end rounded, adjusted to oclusal tooth face, in testing machine EMIC DL2000. The results will be submitted to ANOVA test, with significance level of 5%.
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