Effects of orthodontic force on enamel formation in normal and hypocalcemic rats.

Maxillary incisors of young rats fed a diet deficient in calcium and vitamin D for 4 weeks developed hypoplastic enamel surfaces. In the enamel of maxillary incisors of deficiently fed rats as well as in normal rats, an orthodontic force (50 gm) acting on their incisors for 3-7 days induced foldings in the enamel, globular projections from the surface and marked hypoplastic defects. However, the orthodontic force produced clusters of free-lying enamel matrix only in the nutritionally deficient rats. In view of these observations, it might be concluded that disturbances in enamel formation which cause hypoplasias can be caused both by mechanical trauma and hypocalcemia. Furthermore, it seems that hypocalcemia increases the susceptibility to mechanical trauma of ameloblasts in their secretory stage. Whether the changes in enamel formation noted in the hypocalcemic rats is a direct effect of lowered serum calcium or due to the increase in parathyroid hormone is not known at present.