Tooth eruption and bone resorption: experimental investigation of the ia (osteopetrotic) rat as a model for studying their relationships.

The osteopetrotic (ia) rat was examined as an experimental model for studying the dependence of tooth eruption on bone resorption. In ia rats eruption of incisors and first molars was rare and eruption of second and third molars was reduced and delayed. Autoradiographic studies of 3H-proline incorporation showed that delayed eruption was not due to reduced tooth formation. Microscopic study revealed distortion and failure of posterior growth of the apical ends of incisors, unresorbed bone blocking the eruption pathway for molars, and ankylosis of incisors and first molars to alveolar bone. A reduction in bone resorption, known to be the primary cause of the disease in ia rats, is presumed to be the cause of the delayed or unerupted dentition. The effectiveness of attempts to increase bone resorption in ia rats at an early age by injection of vitamin A and/or parathyroid extract or by parabiotic union with a normal littermate was determined by measuring their effect on the relative size of the tibial marrow cavity. Only parabiosis had a beneficial effect on bone resorption but surgical union could not be performed in animals young enough to affect eruption of incisors and first molars in ia parabionts. These results suggest that parabiotic union of neonatal rats should allow resorption to begin early enough to test the presumed dependence of tooth eruption on bone resorption.