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

羟基磷灰石（HAP）是不可生物降解的，目前尚不清楚M.T.M.是否适用于骨移植。因此，我们观察了正畸牙齿移动过程中HAP骨的组织学变化。将HAP植入比吉犬第二前磨牙附近的人工骨缺损，作为对照，未植入任何材料。种植3个月后，用正畸力移动第二前磨牙。然后进行组织病理学观察。所得结果如下：种植部位的牙齿移动量比对照组小。压力区：在植入区和对照区均观察到破骨细胞对骨的吸收，此外，在HAP附近发生了根吸收。进一步的多核巨细胞紧密附着在HAP上，被骨和结缔组织包围。在保留期内，HAP周围的根与骨之间存在强直。在张力区：观察到来自HAP的额外骨。另一方面，在植入部位用骨填充骨缺损，并控制结缔组织。这些结果表明，HAP中的骨是由破骨细胞溶解的。临床上应避免压力区HAP种植，以免发生牙根吸收和强直。但对于张力区，它似乎是有效的，因为HAP植入产生更多的修复骨。

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.