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Influence of thickener kind and hydrogen peroxide gel viscosity on effectiveness and safety of the bleaching treatment


Objective: The aim of this study will be to understand how the choice of a thickening agent and the viscosity of a 35% hydrogen peroxide gel can influence the chemical reactions occurring inside the gel layer; the way it interact with the tooth structure and produce its primary and secondary effects over the mineralized structure; as well the penetration of the active ingredient though enamel and dentin, responsible by the irritative effect over the pulpal tissue. More specifically the effect of the variables on pH, peroxide decomposition, formation of free radicals and capture of calcium and phosphorus by the bleaching gel, besides its effects over the tooth color and microhardness and the amount of peroxide diffusion through the tooth structure during the treatment time will be analyzed.Materials and Methods: 270 bovine incisors will be selected and enamel/dentin discs obtained from the labial surface, with 6mm of diameter and 2mm of thickness (1mm of enamel and 1mm of dentin). Experimental bleaching gels will be prepared using five different thickening agents (PAP - polyacrylic acid polymer; EC- acrylic copolymer emulsion - Salcare, PAS - sulfonic acid polymer - Aristoflex, SAM - Magnesium aluminum silicate - Bentonita, SP - Fumed silica - Aerosil), which will be added in enough quantity to produce gels with low (L - 30.000 cP), medium (M - 100.000 cP) e high (H - 250.000 cP) viscosities. The samples will be divided into the following experimental groups/subgroups (n=15): PAP/L, PAP/M, PAP/H; EC/L, EC/M, EC/H; PAS/L, PAS/M, PAS/H; SAM/L, SAM/M, SAM/H; SP/L, SP/M, SP/H. In addition, three control groups will be prepared: NTPC (Non Thickener Positive Control) - a hydrogen peroxide solution will used; CPC (Commercial Positive Control) - A commercially available bleaching gel will be used (Whiteness HP, FGM). NC (Negative Control) - the treatment will be performed with purified water. The samples will be placed on artificial pulpal chambers and the bleaching gels applied for 45 minutes. The color change will be evaluated using a colorimetric spectrophotometer (CM-5, Konica Minolta). The enamel surface microhardness change will be measured using a Knoop microhardness tester (FM-700, Future Tech). The change on peroxide content in the bleaching gel will be evaluated using titration with potassium permanganate and a potentiometric titrator (HI902C1-02, Hanna). The amount of free radicals in the bleaching gel will be measured using the Aminophenyl Fluorescein indicator and a multimode microplate reader (SYNERGY HTX, Biotek) in the fluorescence mode. The concentration of calcium and phosphorus in the bleaching gel will be analyzed using a multimode reader (SYNERGY HTX, Biotek) in the absorbance mode. The pH changes of the bleaching gel will be measured using a micro electrode (HI1083B, Hanna). The penetration of hydrogen peroxide into the artificial pulpal chamber will be evaluated using the phenol / aminoantipyrine method and a multimode reader (SYNERGY HTX, Biotek) in the absorbance mode. The data will be statistically analyzed with a significance level of 5%. (AU)

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