The objectives of this in vitro study will be to determine the actual time of decomposition of hydrogen peroxide (HP) and its penetration into the pulp chamber when applied to intact enamel and existing restorations. In Phase I, bovine incisors (60) will be submitted to low concentrations of carbamide peroxide (CP -10%, 15%, 20%) and PH (6%) and high concentrations of PH (35%), with or without light activation (LED, LED; LED/diode laser; halogen), and the decomposition of PH, according to the recommended application time will be determined by pH titration with potassium permanganate. Additionally, the pH of bleaching agents and the color change of dental elements will be measured, to validate the safety and efficacy of the decomposition time, respectively. To determine the penetration of PH in the pulp chamber (phase II) restorations will be made on the labial surface of bovine incisors (240), according to the restorative material (Filtek P90 and adhesive Silorane + Filtek 350 XT + adhesive Adper Easy One) or the surface will remain intact (control). The teeth will be subjected to 5000 thermal cycles. Acetate buffer will be inserted into the pulp chamber before whitening, according to the optimal time of decomposition obtained in phase I. The buffer solution will be added to the collected leucocristais horsedish violet and peroxidase enzyme to determine the optical density of the solutions by spectrophotometry. After bleaching, the area of union enamel-resin will be observed in confocal microscopy to assess the effects of bleaching and the penetration of peroxides in the bonding site. The results obtained within all analyses will be submitted to exploratory data analysis to determine the appropriate statistical test.
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