ENLARGEMENT OF THE RABBIT MANDIBULAR CONDYLE AFTER EXPERIMENTAL INDUCTION OF ANTERIOR DISC DISPLACEMENT - A HISTOMORPHOMETRIC STUDY

Purpose: Clinical and autopsy studies have shown that patients with temporomandibular joint dysfunction are more likely to have enlargement and deformity of the condyle and subsequently occlusal disharmony. However, it is not known what causes this enlargement. This study was designed to test the hypothesis that surgical induction of anterior disc displacement (ADD) in the rabbit craniomandibular joint (CMJ) could lead to enlargement and deformity of the condyle. Materials and Methods: The right CMJ was exposed surgically, and the discal attachments were severed except for the posterior discal attachment (bilaminar zone). Then, the disc was repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. CMJ tissues then were removed after fixation at 24 hours (5 rabbits), 1 week (10 rabbits), 2 weeks (10 rabbits), or 6 weeks (10 rabbits), processed, and stained with hematoxylineosin. Histomorphometric assessment was used to evaluate changes in condylar volume, and thickness of the fibrous, reserve cell, and condylar cartilage layers. Results: The results showed a progressive enlargement of the condylar volume in all experimental joints compared with controls (P <.01). The enlargement was attributable to a significant increase in the cartilage thickness and surface area of the nonarticulating portion of the condyle in the 1-week group (P <.01). In the 2- and 6-week groups, there were significant, progressive increases in cartilage thickness and surface area of the articulating portion of the condyle (P <.01). In all animals, increased cartilage thickness was associated with a decrease in the thickness of the fibrous and the reserve cell layers (P <.01). Conclusion: It is concluded that surgical induction of ADD in the rabbit CMJ causes enlargement of the condyle, which is in part caused by hyperplasia of the condylar cartilage.