A QUANTITATIVE STUDY ON THE MYELINATED FIBER INNERVATION OF THE PERIODONTAL-LIGAMENT OF CAT CANINE TEETH

The periodontal ligament is richly innervated with mechanosensitive af ferent nerve fibers, and the location of the mechanoreceptive terminal s within the ligament is of functional significance. In this study, we have obtained quantitative information on mechanoreceptor distributio n in the lower canine teeth of the cat. Using light microscopy, we qua ntified the number of myelinated axons in the periodontal ligament at 1 mm, 3 mm, and 5 mm from the tooth root apex. Grouped axons and axons which were isolated in the cemental half of the ligament (and therefo re putative mechanoreceptors) were identified. The mean total number o f axons was 1290 (n = 20) at 1 mm from the apex, 1290 at 3 mm, and 814 at 5 mm. The distribution of axons around the tooth root circumferenc e was found to be non-uniform. Near the root apex, the highest numbers of grouped axons were located distally and mesially, and in the middl e region of the root, the highest numbers were found mesially. The hig hest numbers of isolated axons at the apical levels were located dista lly, and in the mid-root region, mesially. At all levels, the lingual region was the most sparsely innervated by both groups. There was a po sitive correlation between the number of grouped axons and the width o f the ligament in the same region, but this correlation was much weake r for isolated axons, suggesting that their distribution does not resu lt only from the volume of tissue. Variations in the number of axons a nd, to a lesser extent, the dimensions of the periodontal ligament wer e considerable. However, these variations were less between left and r ight teeth of the same animal than between teeth in different animals, reinforcing the use of the contralateral tooth as a control for exper iments in which these variables are quantified.