Behavioural responses following tooth injury in rats.

Early changes in spontaneous behaviour (exploration, grooming, freezing, rearing, jaw motion, yawning) and body weight were measured at two and three days after pulp exposure injury and implantation of Fluorogold (FG) into molar teeth of rats. Rats with FG and injuries to three teeth gained weight less rapidly, explored less frequently and froze more often than sham-operated rats. Yawning was not observed in any rats prior to surgery and it was seen more frequently in tooth-injured rats than in sham-operated rats. These results suggest that careful observation of spontaneous behaviour after tooth injuries can be used to assess dental pain in rats and may provide behavioural markers to correlate with anatomical changes after injury. The dental nerve cell bodies that had accumulated transported FG were medium to large, and they only co-localized calcitonin gene-related peptide (CGRP) in a subset of the medium neurons. Chromatolytic or moribund FG-labelled neurons were also found.