Osteoblast differentiation during orthodontic tooth movement

Objectives To analyse the expression of osteoblast differentiation markers and osteoclast activity in the periodontal ligament (PDL) following 2, 4 and 7 days of orthodontic tooth movement (OTM) in an animal model. Setting and Sample Population Eighteen C57BL/6 wild‐type mice. Material and Methods For the OTM model, orthodontic force was applied to the maxillary right first molar using a closed‐coil NiTi spring activated between the molar and incisors. The left side served as the control. Following OTM, the dissected tissues were scanned for micro‐computed tomography (micro‐CT) analysis and processed for histology. Histological stains included tartrate‐resistant acid phosphatase (TRAP) staining for osteoclasts and immunohistochemistry for osteoblast markers alpha‐smooth muscle actin (α‐SMA), osteopontin (OP) and osteocalcin (OC). Results Micro‐CT analysis showed increasing OTM on days 2, 4 and 7 days as well as decrease in bone volume and per cent bone volume at 4 and 7 days. Statistically significant increases in osteoblast marker expression were seen in all groups when compared to the control. TRAP expression was highest at 4 and 7 days, α‐SMA was highest at 2 days and OP/OC was highest at 4 days. Conclusion During OTM, proliferation of pre‐osteoblasts peaks at 2 days while mineralization of the osteoid peaks at 4 days. The osteoclast response is delayed.