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.