The effect of age on morphology and eruption of the lower incisors in mature rats

OBJECTIVE: This study investigated the effect of age on tooth and periodontium morphology and on tooth eruption in the lower incisors of 28 female rats, initial age 10 weeks. DESIGN: Morphometric data of the incisors in three young mature rats (weight 199+/-2.4 g) were compared to that of three 18-week-old (weight 260+/-5 g) animals. The rate of eruption was monitored during 12 months in 11 rats with all teeth in occlusion and in 11 rats with one lower incisor kept constantly out of occlusion. RESULTS:: The incisors continued to enlarge after the animals reached maturity with the size of the teeth increasing both longitudinally and circumferentially. Tooth volume increased by 21%, while that of the periodontal ligament was enlarged by only 12%. The rate of impeded eruption declined steadily from a mean value of 542+/-49 microm/day during the first experimental month to a mean value of 443+/-25 microm/day during the concluding month (p<0.05). The eruption rate of the teeth exceeded that of attrition rate by 2.4%. The unimpeded eruption proceeded steadily throughout the experimental year, at a mean rate of 811+/-12. CONCLUSIONS: Apparently in mature rats age has no effect on the genetic potential as expressed by the unimpeded eruption. In the impeded teeth age does affect the phenotypic expression of the eruptive function governed by occlusal forces as well as by the form and size ratio of the tooth and its PDL.