It has been shown that chemical catalysts added to bleaching agents exert influence on the degradation of hydrogen peroxide (H2O2), what may increase the tooth bleaching efficiency of the product and reduce the diffusion of H2O2 through the dental structure. Therefore, the objective of the present study is to assess the aesthetic outcome, degradation kinetics as well as the transenamel and transdentin toxicity of bleaching gels with 10% and 35% H2O2 chemically activated with different metal oxides. For this purpose, enamel-dentin discs will be bleached with both gels associated with an experimental thickener formulated from the polyacrylic acid and containing or not the chemical activators manganese oxide (MnO) and ferrous manganese oxide (MnFeO). As positive control, a gel with 35% H2O2 will be applied on enamel for 45 minutes. In the negative control, no treatment will be performed. In order to determine the best concentration of these activators (2 mg/mL, 4 mg/mL or 6 mg/mL), the discs will be stained and then bleached with both experimental gels containing different concentrations of MnO and MnFeO (UV-reflecting spectrophotometer, CIE L * a *B* system). The best concentrations will be determined based on the tooth bleaching effectiveness. Then, the degradation rate of the residual H2O2 as well as the production of hydroxyl radicals (HO*) will be determined. To assess the trans-amelodentin cytotoxicity of the experimental bleaching agents, the enamel-dentin discs will be adapted to artificial pulp chambers and the odontoblast-like MDPC-23 cells seeded on their dentin surfaces. Thus, the cell viability (MTT assay) and cell morphology (SEM) will be evaluated. The quantification of the total H2O2 able to diffuse through the discs will also be determined (leuco-crystal violet/peroxidase assay). The numerical data obtained in this laboratorial will be submitted to specific statistical analysis.
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