The effect of cortisone on the eruption rate of root-resected incisors in the rat.

It is generally thought that the periodontal ligament plays a key--perhaps even exclusive--role in tooth eruption. The present study was designed to test the hypothesis that the fundus also may contribute to the process. To this end the effect of cortisone on the eruption rate of root-resected mandibular incisors was examined in male albino rats. Half of the animals received daily injections of cortisone; the other half were given normal saline. Impeded and unimpeded eruption rates were measured at 3-day intervals and tested for between- and among-means differences by repeated-measures analysis of variance (ANOVA). In contrast to the acceleration commonly seen in intact incisors, cortisone produced no change in the eruption rate of root-resected incisors. It was concluded therefore that the accelerative effect of cortisone is mediated by the fundus, rather than the periodontal ligament. Further, it is hypothesized that early eruption is controlled by cellular proliferation within the fundus; however, once the tooth enters the oral cavity and becomes functional, the periodontal ligament matures and becomes the dominant factor in subsequent eruption.