Tooth movement and alveolar bone reaction after corticotomies have not been thoroughly examined. In this study, the effects of corticotomies on orthodontic tooth movement and alveolar bone reaction were investigated in dogs.Corticotomies were performed on the cortical bone of the mandibular left third premolar region in 12 male adult beagles. The third premolars on the left experimental side and on the right sham side were moved mesially with a continuous force of 0.5 N.Tooth movement velocities from 0 to 1 week and from 1 to 2 weeks after the corticotomies were significantly faster on the experimental side than on the sham side. Hyalinization of the periodontal ligament appeared only at 1 week after the corticotomies on the experimental sides, whereas it was observed from 1 to 4 weeks after the corticotomies on the sham sides. Tartrate-resistant-acid-phosphatase positive cells of the experimental side tended to work vigorously at an early time on the alveolar wall and in the bone marrow cavities.Orthodontic tooth movement increased for at least 2 weeks after the corticotomies. This might be brought about by rapid alveolar bone reaction in the bone marrow cavities, which leads to less hyalinization of the periodontal ligament on the alveolar wall.