Experimental Pharmacologic Studies on the Alveolar Bone Resorption and its Recovery Mechanism.

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1. Histological changes of alveolar bone in the area of molar tooth were investigated in the rats fed a low calcium diet (0.05% Ca, 0.35% P). Bone resorption was found to be progressively appeared in the cancellus bone around the tooth after feeding a low calcium diet, however, the alveolar bone proper remained suggesting that the function of alveolar bone to support the functional activity of tooth in occlusion was still maintained.2. To investigate the recovery process from the bone resorption of alveolar bone, rats were given a low calcium diet for 9 days and were subsequently replaced by a control diet (0.5% Ca, 0.35% P) for 11 days. The bone volume increased significantly after feeding the control diet, but it was not enough to recover the bone resorption induced by the low calcium diet. It was suggested that once bone resorption is occurred, a longer period is needed to recover the loss of bone volume compared with the period to induce bone resorption by the low Ca diet.3. To elucidate the function of the cytoskeletal system in osteoclasts during bone resorption, osteoclasts were isolated from the tibia of rats and were cultured under the treatment of a microtubule inhibitor, colchicine. Osteoclasts were contracted when microtubules were destroyed by colchicine. They were separated into several cell portions and each cell portion was moving toward a different direction. These results indicated that microtubules are important to maintain the cell shape of osteoclasts as a cytoskelton and that they control the movement of each cell portion in order to keep the cellular activities of a multinucleated osteoclast being as one cell.