Metallic oxides as chemical catalytic agents of experimental bleaching gels: chemical, biologic and esthetic evaluation

Abstract

Bleaching therapies based on hydrogen peroxide (H2O2) gels have proven clinical efficacy; however, post-bleaching sensitivity is the main adverse effect related with these techniques. It has been shown that the intensity of this adverse effect is related with the amount of residual H2O2 capable to reach the pulp tissue. It has been shown that by adding substances capable of catalyzing H2O2 degradation into free radicals increase bleaching efficacy and reduce the trans-enamel and trans-dentinal diffusion of residual H2O2. Thus, the objective of the present study is to manipulate experimental low-concentrated H2O2 bleaching gels (10% and 20% H2O2) associated with manganese oxide (MnO) and ferromanganese oxide (MnFeO) as catalytic agents. The bleaching gels will be manipulated from a 35% H2O2 stock solution, and the thickener will be formulated with polyacrylic acid compound, which will be associated or not with 1mg/ml MnO or MnFeO. Free radical and hydroxyl ions release will be evaluated. For cytotoxicity assays, 3.5 mm thick enamel/dentin discs will be submitted to an intrinsic staining protocol. These discs will be adapted into artificial pulp chambers, and this set will be placed in 24-well culture plates. The bleaching gel will be applied onto enamel surface for 45 minutes. The trans-enamel and trans-dentin components (extract) will be applied during 1 hour to previously cultured pulp cells. Cell viability (MTT) and oxidative stress (H2DCFDA) will be evaluated. Enamel color change will be measured by means of a UV-vis reflection spectrophotometer (CIE L * a * b *). Numerical data will be submitted to specific statistical analysis. (AU)