The objective of this project is to quantitatively evaluate in vivo the effect of antimicrobial photodynamic therapy in the treatment of experimentally induced periapical periodontitis. Will be used 70 premolars of dogs (140 roots) which, after induction of periapical lesions, will be divided into 8 groups: In groups I and V (20 roots each) after biomechanical preparation, the root canals are filled with pasta Calen ® for 15 days, followed by filling with AH Plus. In Groups II and VI (20 roots each): after biomechanical preparation, the root canals with fotossensitizador be prejudged based on phenothiazine concentration of 10 mg / ml for 1 minute, after that period, the root canals are irrigated with distilled water sterilized and irradiated with a diode laser with wavelength of 660nm and maximum power of 60mW/cm2, powered by battery 20 mW, via the fiber optic flexible tip diameter of 0.6 mm. The fotossensitizador be irradiated as recommended by the manufacturer for 1 minute in a continuous wave mode and filling with AH Plus. In groups III and VII (20 roots each) after biomechanical root canals will be filled in the same session with AH Plus and groups IV and VIII (10 roots each) after biomechanical channels remain empty. Then, the teeth of all groups will be restored with amalgam of silver, based on a glass ionomer. After the experimental period of 28 ± 3 days (Groups I, II, III and IV) and 90 ± 5 days (Groups V, VI, VII and VIII), the animals will be killed, their mandibles and jaws and teeth removed submitted histotechnical processing and later be deparaffinized and hydrated for immunohistochemical analysis. Longitudinal sections of 5 mm will be obtained and stained with hematoxylin and eosin, Masson's and Mallory Brown & Brenn. Microscopical analysis by quantitative method is recorded full description of the characteristics of apical and periapical tissues and conducted to quantify the number of inflammatory cells and the extents of the areas of periapical periodontitis, bone resorption, resorption apical (cementum and dentin) and edema in mm2. Immunohistochemical analysis will be performed to identify and locate the factors involved in osteoclastogenesis and the cuts will be subjected to immunohistochemistry by using primary antibodies to RANK, RANKL and OPG. The immunostainings will be evaluated throughout the length of the tooth root, periodontal ligament, alveolar bone and flesh and the results will be expressed in a quantitative way. Evaluations will be held on Imager.M1 Axio microscope (Zeiss) coupled to an AxioCam MRC5 camera (Zeiss). The values will be evaluated as to the type of distribution groups and compared by analysis of variance (ANOVA) or the nonparametric Kruskal-Wallis test, with significance level of 5%.
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