Long-term bleaching treatment without professional supervision with over-the-counter products, especially those used continuously and repeatedly (over-bleaching), can provide irreversible changes in the organic and inorganic components of the dentin matrix, affecting its mechanical behavior. Thus, the aim of the present study will be to characterize the organic and inorganic chemical structures of the dentin matrix and to evaluate its dynamic mechanical behavior when subjected to a long-term treatment (over-bleaching) with an over-the-counter bleaching agent. The following bleaching treatments will be evaluated: control (no treatment), at-home bleaching technique in professionally prescribed tray with 10% carbamide peroxide (Opalescence PF 10% / Ultradent Products) and over-the-counter preloaded strips with 9.5% hydrogen peroxide (Crest 3D White Luxe Glamorous White Whitestrips). The bleaching treatments will be performed on human dentin demineralized beams with 37% phosphoric acid for 5 hours, according to the manufacturers instructions, for 14 days. After 14 days of storage, the bleaching treatments will be re-applied according to the protocol previously described for 14 days, simulating a clinical situation in which the patient uses the bleaching agent without the dentist's supervision for a time not recommended by the manufacturer (over-bleaching). Dynamic mechanical tests will be performed at different times (baseline, after 7 and 14 days of treatment, after a 14-day interval, after another 7 and 14 days of use (over-bleaching time). The load will be applied with a 1Hz frequency, 0.01 N of pre-applied force and gradual displacement with amplitude of 1 to 100 ¼m, under immersion in distilled water at room temperature, obtaining the values of the elastic component of the dentin matrix. The mineral (relative presence of minerals and crystallinity) and organic (normalization, crosslinking, nature and secondary collagen structure) components of dentin will be evaluated by Raman spectroscopy at the same times previously described. For the data obtained in the dynamic mechanical analysis, the values of E ', E ", E * and tan ´ will be statistically analyzed to evaluate the variance homogeneity and normal distribution, possible using two-way ANOVA (± = 0.05) and Tukey test for comparisons between the groups. For the characterization of chemical interactions by Raman spectroscopy, the biochemical content of each group will be analyzed using the average of the spectra.
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