An experimental study on histopathological changes of alveolar bone around hydroxyapatite during orthodontic tooth movement.

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It the been unclear whether M.T.M. is acceptable in the cases treated with bone graft using hydroxyapatite(HAP), which is not bio-degradable. So we examined histological changes of bone among HAP during orthodontic tooth movement. HAP was implanted into artificial bone defects adjacent to second premolars in beagie dogs, and as control no materials was implanted into them. Three months after implantation, the second premolars were moved with orthodontic force. Then they were observed histopathologically. The results obtained were as follows.Amount of movements of the teeth in implanted sites were smaller than control. At pressure zone : Resorptions of bone by osteoclasts were observed both in implanted and control sites, in addition, root resorptions occured adjacently to HAP. Further mutinucleated giant cells closely attached to HAP surrounded by bone and connective tissue. In retention period there was ankylosis between roots and bone around HAP. At tension zone : additional bone from HAP was observed. Bone defects were filled with bone in implanted sites, on the other hand, with connective tissue in control.These results suggested that bone among HAP was resolved by osteoclasts. Clinically, HAP implantation for pressure zone should be avoided because of the occurence of root resorption and ankylosis. But for tension zone it seems to be effective because HAP implantation produces more repaired bone.