Tooth eruption depends on bone resorption: experimental evidence from osteopetrotic (ia) rats

Resorption of alveolar bone around erupting teeth is known to be independent of tooth eruption. However, the failure of tooth eruption and reduction in bone resorption in the osteopetrotic rat mutation, incisors absent (ia), suggest that tooth eruption depends upon bone resorption. This hypothesis was tested by determining the effects of neonatal restoration of bone resorption in ia rats on eruption of first molars. Newborn ia rats were treated with irradiation and spleen cells and tooth eruption and bone resorption were examined 30 days later. In 24 treated ia rats at least two molars erupted in every rat and all four molars erupted in 14. In 24 untreated ia littermates, no molars erupted in 21, one molar erupted in two and two molars erupted in one rat. All molars erupted in 38 untreated normal littermates. Alveolar bone overlying unerupted first molars in untreated ia rats was not present in treated mutant littermates. Neonatally treated ia rats had osteoclasts with ruffled borders and no skeletal sclerosis by 30 days. Within 48 hours after treatment two types of osteoclasts could be found in treated rats. One type resembled those found in untreated ia littermates and the other those found in normal rats. These data suggest that failure of tooth eruption in ia rats is directly related to the reduction in bone resorption and that alveolar bone resorption is required for tooth eruption.