Despite of the decline of the dental caries in Brazil and around the world, this disease is still common mainly in polarized groups affecting children. Thus, this high caries risk group needs great dental attention and also novel treatment techniques which give priority to minimal intervention. Studies about the photodynamic therapy have already demonstrated the susceptibility of cariogenic bacteria to death when used associated with photossensitisers and activated with a light source. Therefore, the aim of this study will be to compare, in vivo, the antimicrobial effect of two photodynamic therapies, associate with dyes, in the deciduous carious dentin. This study will be conducted in patients between 3 and 9 years old, with presence of deep caries lesion in any deciduous molar, without any pain sintomatology compatible with reversible pulpites. The children will be divided in three groups (n = 15). Control (C), PDTLED (photodynamic therapy - LED) and PDTFL (photodynamic therapy - laser). The selected patients will be submitted to initial clinical examination and standardized bitewing radiographs will be taken in each side before the treatment, immediately after, 6 and 12 months after the end of the treatments. They will also be clinically followed up as regards to pain sintomatology throughout the same periods. The number of viable microorganisms, total level of bacteria and the proportion levels of S. mutans, Lactobacilos casei, Fusobacterium nucleatum, Atopobium e Bifidobacterium will be established by quantitative PCR. The number of rRNA gene copies of each bacterial specie/group will be normalized by variance analysis and Tukey test. For the radiographs, a quantitative analysis of the intra-examinator reproducibility assessment will be performed (Cohen´s kappa). The subtraction data reproducibility will be analyzed using an intra-class correlation coefficient. The mean control areas of the dentin and of radioluscence of each followed period will be compared by the multiple variance analysis and Tukey test of multiple comparisons. The variation between the radioluscent areas, accordingly to the period, will be compared using the Friedman rank for repeated measures analysis. The significance level for all statistical analysis will be fixed in 5%.
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