The aim of this in vitro study was to evaluate the calcium and phosphorous content in human dental enamel before, during and after bleaching treatments with hydrogen peroxide (HP). Forty eight third human molars will be divided into six groups (n = 8) to receive the application of "bleaching agents containing high concentration of HP" - Whiteness HP Maxx/ FGM (35% HP); Whiteness Blue HP / FGM (35% HP + 2% calcium gluconate); Pola Office +/ SDI (37.5% HP + 5% potassium nitrate); Opalescence Boost/ Ultradent (38% HP + 1.1% fluoride and 3% potassium nitrate) - and "bleaching agents containing low concentration of HP" - Pola Day/ SDI (9.5% HP); White Class 10%/ FGM (10% HP + potassium nitrate + calcium + fluoride). These agents will be applied to dental enamel surfaces according to the manufacturer's instructions. To determine the amount of calcium and phosphorous in enamel, samples form enamel surface will be obtained by using the microbiopsy enamel technique at different times (before, during and after bleaching treatment). The calcium and phosphorus amount will be obtained in micrograms per milliliter (g/ ml) by using total reflection of X-rays methodology (TXRF). The data will be tabulated into spreadsheets in Microsoft Office Excel 2012 for the statistical analysis and ANOVA will be applied if there is homogeneity of variance followed by Tukey test. Otherwise, non-parametric tests will be used.
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