Bone grafts may be indicated in areas with bone deficiencies. Studies in animals have demonstrated that laser therapy can improve bone healing, although this mechanism of action is not completely elucidated. The purpose of this study will be to histomorphometrically analyze the influence of low-level laser therapy and a heterogenous bone graft on bone healing of critical size defects surgically created with a trephine of 10 mm in calvaria of 64 male rats (Rattus norvegicus albinus, Wistar). The animals will be assigned to one of 4 experimental groups according treatment: Group 1 - Control - defect filled with a blood clot only (C); Group 2 - defect treated with low-level laser therapy (GaAlAs laser with 660 nm) (LLLT); Group 3 - defect filled with heterogenous bone graft (Gen-mix) (EO); Group 4 - defect filled with heterogenous bone graft, Gen-mix, associated to low-level laser therapy (LLLT+EO). The defects treated with Laser will be irradiated in 8 peripheral points and in 1 central point (40 mW, 2 J/cm2/point). To each group, 8 animals will be submitted to euthanasia in the period of 30 and 60 days. The area removed will be fixed and submitted to a routine laboratory processing. Semi-serial sections 6 micrometers thick will be cut and stained with hematoxylin and eosin. The histologic analysis will be performed using light microscopy. Histometric evaluation will be performed and the data will be statistically analyzed.
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