Facing the importance and prevalence of dental erosion in children, mainly due to gastroesophageal reflux and lack of studies in the literature on the effects of the CO2 laser in the control of erosion, the objective of this study will be to determine the influence of different outputs of the CO2 laser associated with a source of fluoride in vitro in the control of erosion in primary teeth enamel. Seventy-five primary teeth will be used for the procurement of 150 fragments of enamel (3x3 mm). These will be covered with nail enamel, and the lower portion will be set a thong. Below, will be individually embedded in polyester resin, with the surface of enamel side up. For training injury of erosion, the specimens will be submitted to a challenge acid initial cycles of 2 by 1 minute, made the same day, with hydrochloric acid solution (pH 1.2) that simulates the gastric juice. The specimens will be randomly divided into 2 groups according to the superficial treatment to be made: I. 2% acidulated phosphate fluoride gel (APF) and II. placebo gel (control). Then, the specimens from each group will be divided in 5 subgroups, according to the parameters used in the laser irradiation with CO2: A. 1 W, B. 2 W, C. 3 W, D. 4 W, E. Absence of irradiation (control). The CO2 laser irradiation will be held in a non-contact, defocused at a distance of 4 mm of enamel. After the completion of the treatments, will be simulated erosive new challenges in hydrochloric acid solution (pH 1.2) for 5 days, and made 2 cycles of 1 minute per day. Subsequently, the method of histochemical staining, the specimens will be individually immersed in solutions of copper sulphate to 10% and rubeanic acid. After staining, will be obtained three sections and an examination of the permeability will be held on optical microscope, using the software, scanning and image Axion Vision 3.1. Will be held in each cut, five evaluations of the penetration of copper ions in relation to the total thickness of the enamel, totaling fifteen readings per specimen. For statistical analysis, will be considered the average of these measurements.
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