The present study aims to evaluate the color change, cytotoxicity and trans-enamel and trans dentinal penetration of hydrogen peroxide in bovine enamel/dentin disks submitted to the process of tooth whitening with a 35% hydrogen peroxide bleaching gel (Whiteness HP Maxx - FGM Dental Products). The specimens will be divided into 8 groups (n = 12) according to the factors studied (light sources and acid etching): I- bleaching gel not exposed to any light source; II- gel exposed to halogen light (Ultralux-Dabi Atlante, Ribeirão Preto, SP, Brazil), III- gel exposed to LED (DB 686 - Dabi Atlante, Brazil), IV- gel exposed to LED / LASER source (Whitening Lase II, DMC Equipment Ltda, São Carlos, SP, Brazil). Specimens of groups V, VI, VII and VIII will be pre-conditioned with 37% phosphoric acid (Dental GelConditioner - Dentisply, Brazil) and submitted to the same treatments described for groups I, II, III and IV, respectively. To quantify the penetration of hydrogen peroxide, specimens will be placed in an artificial pulp chamber (APC) containing acetate buffer solution, which will be collected for evaluation of optical density in a spectrophotometer. The analysis of color changes will be held on the same equipment. Readings will be done before the bleaching procedure, six days after each session and 14 days after completing the treatment. For cytotoxicity analysis, the specimens will be placed in APCs and the extracts (bleaching product + culture medium) will be applied on MDPC-23 odontoblasts, in cell culture for 1 hour. Cell viability will be assessed by the MTT assay. Data will be checked for homogeneity and homoscedasticity for determining the most appropriate statistical tests. The significance level will be set at 5%.Keywords: Dental Bleaching; light source; acid-etching enamel; trans-enamel penetration; trans-dentinal penetration; Cytotoxicity.
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