To investigate the mechanism of alveolar bone remodeling in response to orthodontic force application, we examined the distribution of osteoclasts and pre-osteoclastic cells using quantitative immunohistochemistry of vacuolar type H(+)-ATPase. For orthodontic force to be produced by the Waldo method, an orthodontic elastic band was inserted between the upper first and second molars of rats. The observed areas of periodontal tissues around second molars were the distal surfaces of mesial roots, as the pressure side, and the mesial surfaces of distal roots, as the tension side. Specific expression of vacuolar-type H(+)-ATPase at the ultrastructural level was detected in mononuclear and multinucleated pre-osteoclastic cells, as well as osteoclasts with ruffled borders on bone surfaces. At 6 hrs after orthodontic force application, many osteoclasts and pre-osteoclastic cells with H(+)-ATPase expression were first observed in vascular canals of the alveolar bone crest near the pressure side of the periodontal ligament, but the number of osteoclasts was not increased in the periodontal ligament. On day 1 after tooth movement, osteoclasts were increased in number in the periodontal ligament and in adjacent alveolar bones on the pressure side, but were seldom observed in corresponding areas on the tension side. The number of osteoclasts increased until day 7, but had decreased by day 14. These results suggest that, in bone remodeling during experimental tooth movement, (1) osteoclasts and pre-osteoclastic cells can be identified by H(+)-ATPase immunohistochemistry, (2) osteoclasts and pre-osteoclastic cells are rapidly induced after force application, (3) osteoclast induction first occurs in vascular canals of the alveolar bone crest on the pressure side, and then, (4) the number of osteoclasts increases in the periodontal ligament on the pressure side.
Alveolar Bone Loss Alveolar Process