In the face of the benefits of selective caries removal using Er:YAG laser and attempting to stabilize the dentin collagen structure to improve the mechanical integrity of caries-affected dentin, it is relevant to evaluate in vitro the effect of the selective removal of caries lesion using Er:YAG laser and the dentin biomodification with an experimental compound of phosphorylated chitosan nanoparticle (NanoPC). It will be evaluated the: dentin microbiology, chemical composition of the dentin, micro hardness of the dentin subsurface, micro-shear bond strength and the morphology of the adhesive interface after 24 h and 18 months of hydrolytic degradation. The sample will be composed of 224 human third molars submitted a microbiological method to produce dentine caries lesions. Selective removal of the caries lesion will be performed using the Er:YAG laser (250mJ/4Hz) or but at low-speed handpiece (conventional method). The teeth will be divided according to the dentin biomodification: without biomodification (control) or NanoPC for 1 min. Specimens will be submitted to microbiological evaluation by counting of colony forming units of Streptococcus mutans (n=10), microhardness analysis of dentin subsurface at different depths (30, 60, 90 and 120 ¼m from the surface) (n=10) and analysis of the absorption peaks of the phosphate groups, carbonate, organic matrix bands and water (n=10) by FTIR. All analyzes will be performed after induction of the caries lesion, after the selective removal of the caries lesion and after the dentin biomodification. For bond strength analysis, the specimens will receive adhesive system (Single Bond Universal-3M) and composite resin (Z250-3M), and will be submitted hydrolytic aging for 24 h or 18 months. Afterwards, specimens will be submitted to micro-shear bond strength analysis (n=10) and morphological analysis of adhesive interface by MEV (n=3). The selection of statistical tests will be based on the characteristics of the data set for each variable. The statistical inferences will be made considering the significance level of 5%.
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