The effects of aging on the eruptive behavior of the mandibular incisor in male rats

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.

Apoptosis in the connective tissues of the periodontal ligament and gingivae of rat incisor and molar teeth at various stages of development

Apoptosis in the periodontal connective tissues was studied using the TUNEL technique, supported by electron microscopy. For 16 rats (aged 3, 8, or 104 weeks), nuclear fragmentation was assessed using the TUNEL technique (for 4 of the animals aged 8 weeks, incisor eruption was experimentally increased by trimming of teeth to the gingival margin--unimpeded eruption). A further 8 rats (aged 8 and 104 weeks) were employed for electron microscopy. For the incisor, prior to aging, and regardless of eruptive behavior (i.e., for both impeded and unimpeded incisors), there was little evidence of apoptosis in the periodontal ligament or gingival connective tissues. For the molar, apoptosis was also not usually detected when the teeth were erupting or in the mature, erupted state. In the aged animals, however, there was a marked increase in apoptosis (as assessed by the TUNEL technique) within the periodontal ligament and gingivae of both the molars and incisors (where eruption rates also increased). Nevertheless, electron microscopy indicated that significant numbers of apoptotic cells were only in the incisor periodontium. These findings are not consistent with the view that the periodontal fibroblasts provide a component of the force(s) responsible for eruption.