The effect of altered bone metabolism on orthodontic tooth movement.

The purpose of this study was to determine how bone remodeling changes induced by nutritional hyperparathyroidism affect tooth movement through alveolar bone. Twelve beagle dogs, approximately 1 year old, were randomly divided into two groups of six. The controls were fed a standard dog diet (calcium 0.54 percent, phosphorus 0.42 percent). The experimental diet was identical to that fed the controls except for a decrease in the calcium (0.12 percent) to phosphorus (1.20 percent) ratio. At the tenth week of diet administration, following extraction of the lower third premolars, the second and fourth premolars were moved toward each other with a reciprocal elastic force of 100 Gm. Twelve weeks later the animals were killed and the mandibles were prepared for laboratory evaluation, which included Paragon 1301 staining of undecalcified sections, scanning electron microscopy, and a bone ash analysis. Radioimmunoassays during the experiment showed that the test animals had significantly elevated levels of parathyroid hormone, indicating a probable state of hyperparathyroidism. The clinical data revealed more rapid tooth movement in the experimental animals. Laboratory data indicated that the hyperparathyroid animals had significantly decreased bone density, as well as bone remodeling changes consistent with high PTH levels. These findings suggest that, in addition to applied force, tooth movement is dependent upon the state of calcium metabolism in alveolar bone.