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Influence of chemical catalyst on bleaching efficiency of hydrogen peroxide


The aim of this study will be to evaluate the effect of different kinds and concentrations of chemical catalysts, in various pHs, on the bleaching efficiency of hydrogen peroxide. Besides that, to verify whether the catalysis allows the use of smaller peroxide concentrations without reduction of the efficiency. For that, inside a reactor with controlled temperature it will be mixed an association of chromogenic substances (red wine, tobacco and coffee), hydrogen peroxide in an amount enough to get a final concentration of 35%, substances for pH adjust (HCl or NaOH) and various concentrations of different chemical catalyst. It will be tested catalyst based on iron ions (13 complexes, 1 nitrate, 1 sulphate and 2 chlorite) and manganese (5 complexes, 1 nitrate, 1 sulphate and 1 chloride), each one in 10 different concentrations. The pH of the mixture for each concentration will be adjusted to 5.5, 7 and 9. Control groups without catalyst, for all three tested pH will also be evaluated. One sample will be prepared for each catalyst in each concentration and pH, and kept at 30oC during the whole process. After the mixture, the baseline color of the solutions, its pH and hydrogen peroxide concentration will be evaluated by a colorimetric spectrophotometer (CM-5, Konica Minolta), pHmeter and automatic tritator, respectively. During the reaction, sequential reading will be performed each 5 minute, during 30 minutes. The control group with the pH more efficient in producing the bleaching will be determined (35% Positive Control). After that, four combinations of the parameters kind of catalyst/concentration of the catalyst/pH, which produced the more intense bleaching effect than 35% Positive Control group, will be tested in relation the possibility of peroxide concentration reduction, keeping its bleaching efficacy. Whether any catalyzed solution with reduced peroxide concentration produces a bleaching similar or more intense than the control, it will be included at the last stage of the study, as well a non-catalyzed control with the reduced concentration selected (Reduced Positive Control). In this stage, 220 enamel/dentin samples will be obtained from bovine incisors and distributed in 11 groups (n=20), according to the bleaching solution to be employed: 35% Positive Control, Reduced Positive Control, 4 catalyzed 35% hydrogen peroxide solutions, 4 catalyzed solutions with reduced concentrations of hydrogen peroxide and a negative control group that will not receive dental bleaching. The color and microhardness of the samples will be evaluated before and after bleaching. The data of color change (Delta E) and the percentage of microhardness change will be statistically analyzed.Expected results: With these analyses is expected to determine what catalyst is the most effective in increasing the efficiency of the bleaching process, what pH is more adequate for its use, as well to understand the effects of this catalyst in the extinction of the available peroxide and on the maintenance of a pH considered safe for clinical use. The understating of the reaction kinetic will allow the development of more efficient and safe dental bleaching gels, maybe with reduced peroxide concentrations and less toxicity to the pulp. (AU)

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