The effect of cyclophosphamide on the eruption of impeded and resected incisors in rats.

It is known that a single dose of cyclophosphamide (40 mg.kg-1 intraperitoneal) slows the eruption of unimpeded incisors but has no effect on impeded incisors. In this study incisors that were impeded when cyclophosphamide was given were subsequently made unimpeded. When they were unimpeded they erupted more slowly than the controls. Therefore the changes cyclophosphamide produces which slow eruption are formed in impeded incisors but have an effect only in unimpeded incisors. It has been reported that cyclophosphamide slows the eruption of resected incisors when it is given before the resection. In a second experiment cyclophosphamide was given after the resection and had no effect on eruption rates. It is suggested from these and earlier findings that cyclophosphamide slows eruption by imposing a maximum on the rate at which it can occur and that it does so through the changes it produces in the periodontal ligament. The periodontal changes make it harder for the tooth to move rather than altering the forces moving the tooth. This explanation of how cyclophosphamide slow eruption produces an alternative interpretation of some, but not all, of the findings that have been cited as evidence that there are two mechanisms of tooth eruption.