Microhardness of human enamel submitted to different bleaching agents containing hydrogen peroxide (HP) with high or low concentrations, added or not with calcium and/or fluoride

Abstract

The aim of this work is to in vitro evaluate the microhardness of human enamel submitted to different bleaching agents containing hydrogen peroxide (HP) with high or low concentrations, added or not with calcium and/or fluoride for home-use or in-office bleaching techniques. Sixty enamel fragments will be obtained from 30 human third molars. They will be divided into six groups (n=10). High concentration HP agents will be used in four groups: Whiteness HP Maxx/ FGM (HP 35%), Whiteness HP Blue/ FGM (HP 35% + 2% of calcium gluconate), Pola Office +/ SDI (HP 37.5% + 5% of potassium nitrate) and Opalescence Boost/ Ultradent (HP 38% + 1.1% of fluoride and 3% of potassium nitrate); and two low concentration HP agents will also be use: Pola Day/ SDI (HP 9.5%) and White Class 10%/ FGM (HP 10% + potassium nitrate + calcium + fluoride). The enamel microhardness will be measured quantitatively in Knoop Hardness Number (KHN) before, during and after bleaching treatment in six different times. If there is homogeneity of variance and normal distribution of errors of mathematical model, the quantitative assessment of microhardness data will be made by analysis of variance. Response surface curves can be obtained for the representation of the microhardness value. Otherwise, nonparametric methods will be used. At the same time, a study will be conducted by the same research team that will quantify the amount of calcium and phosphorus in enamel submitted to the same bleaching agents and times by using the technique of x-ray fluorescence by total reflection. Analyzing both results, it will be evaluate the existing correlation between the data.