By promising results obtained in studies using sodium trimetaphosphate (TMP) in an attempt to reduce mineral loss caused by dental caries, it has been created the possibility of the use of TMP associated with hydrogen peroxide (HP). Since the dental bleaching could cause mineral loss of enamel. Thus, the objective of this study will be to evaluate in vitro the addition of TMP in concentrations of 1% and 10% with 0.1% sodium fluoride (NaF) or not into 6% hydrogen peroxide on the enamel surface and in depth, using microhardness test and polarized light microscopy (PLM). Initially 180 bovine tooth enamel surface will be analyzed by microhardness test to a uniform selection of 90 discs of enamel/dentin with hardness closer to the median. Subsequently, the specimens will be randomly divided into nine groups (n = 10): G1: control (deionized water); G2: placebo (carbopol); G3: PH; G4: PH + NaF; G5: PH + 1%TMP; G6: PH + 1%TMP + NaF; G7: PH + 10%TMP; G8: PH + 10%TMP + NaF; G9: 6% White Class (FGM - Dental Products). The bleaching treatment will be performed daily during 14 days for 1.5 hours per session. Then, the discs will be sectioned in the middle, half of samples will be for analysis of superficial enamel microhardnessand the other half will be embedded in epoxy resin and polished for analysis of subsurface enamel microhardness. After specimens in-depth analysis, approximately 300¼m slices will be obtained and polished to 150¼m thickness for MLP analysis. The microhardness values and the results obtained by qualitative images by MLP will be subjected to statistical analysis at a 5% significance level.
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