Mechanism of action and morphologic changes in the alveolar bone in response to selective alveolar decortication-facilitated tooth movement

Background and Purpose: The aim of this study was to test if corticotomy-induced osteoclastogenesis and bone remodeling underlie orthodontic tooth movement and how selective alveolar decortication enhances the rate of tooth movement. Materials and Methods: A total of 114 Sprague-Dawley rats were included in 3 treatment groups: selective alveolar decortication alone (SADc); tooth movement alone (TM); and "combined" therapy (SADc + TM). Surgery was performed around the buccal and palatal aspects of the left maxillary first molar tooth and included 5 decortication dots on each side. Tooth movement was performed on the first molar using a 25-g Sentalloy spring. Measurements were done at baseline (day 0: no treatment rendered) and on days 3, 7, 14, 21, 28 and 42. Microcomputed tomography, Faxitron analyses, and quantitative real-time polymerase chain reaction (q-PCR) of expressed mRNAs were used to assess changes. Results: The combined group showed increased tooth movement (P = 0.04) at 7 days compared with the tooth movement group with significantly decreased bone volume (62%; P = 0.016) and bone mineral content (63%; P = 0.015). RNA markers of osteoclastic cells and key osteoclastic regulators (M-CSF [macrophage colony-stimulating factor], RANKL [receptor activator of nuclear factor kappa-B ligand], OPG [osteoprotegerin], calcitonin receptor [CTR], TRACP-5b [tartrate-resistant acid phosphatase 5b], cathepsin K [Ctsk]) all showed expression indicating increased osteoclastogenesis in the combined group. RNA markers of osteoblastic cells (OPN [osteopontin], BSP [bone sialoprotein], OCN [osteocalcin]) also showed increased anabolic activity in response to the combination of alveolar decortication and tooth movement. Conclusions: The data suggest that the alveolar decortication enhances the rate of tooth movement during the initial tooth displacement phase; this results in a coupled mechanism of bone resorption and bone formation during the earlier stages of treatment, and this mechanism underlies the rapid orthodontic tooth movement. (Am J Orthod Dentofacial Orthop 2011; 139:S83-101)