Hypothermic insult to the periodontium: a model for the study of aseptic tooth resorption

The aim of the current investigation was to define an animal model for the study of hard tissue resorption by examining the responses of the periodont al ligament (PDL) to both single and multiple episodes of hypothermic injur y to the crowns of rat teeth. A group of 12 male rats weighing 200-250 g we re anesthetized, and pellets of dry ice (CO2) were applied once to the crow ns of the right first maxillary molars for continuous periods of 10 or 20 m in. Animals were sacrificed at 2, 7, 14 and 28 days and tissues were proces sed for routine histological examination. A second group of eight animals a nd a third group of 12 animals were subjected to three applications of dry ice over a period of I week and sacrificed at 2 and 14 days respectively af ter the final application. In addition to thermal insult, the periodontium of teeth from a fourth group of six rats was subjected to mechanical trauma . Examination of the sections from the group undergoing a single freezing e pisode revealed that, by 1 week, shallow resorption lacunae had appeared on the root surface. These became more extensive after 14 days. At the same t ime hyaline degeneration was evident in the PDL. Within this group, teeth s ubjected to the longer 20-min application times generally showed more exten sive injuries. By 28 days, evidence of repair was observed with reparative cementum beginning to line the resorption lacunae in the root dentin. Secti ons from animals subjected to multiple episodes of thermal trauma and those subjected to additional mechanical insult showed more extensive external r oot resorption than those from single-injury animals. It was concluded that low temperature stimuli applied to the cro crowns of rat molars were capab le of eliciting a sterile degenerative response in the PDL which, in turn, resulted in external root resorption. Furthermore, the degree of this tissu e injury was commensurate with the duration and number of exposures to the trauma. The results also indicated that progression of the resorptive proce ss required periodic exposure to the injury, in the absence of which repair to the damaged root occurred.