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 te mporomandibular joint dysfunction are more likely to have enlargement and deformity of the condyle and subsequently occlusal disharmony. How ever, it is not known what causes this enlargement. This study was des igned to test the hypothesis that surgical induction of anterior disc displacement (ADD) in the rabbit craniomandibular joint (CMJ) could le ad 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 zygomati c 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 r abbits), 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 show ed a progressive enlargement of the condylar volume in all experimenta l joints compared with controls (P <.01). The enlargement was attribut able 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, progre ssive increases in cartilage thickness and surface area of the articul ating portion of the condyle (P <.01). In all animals, increased carti lage thickness was associated with a decrease in the thickness of the fibrous and the reserve cell layers (P <.01). Conclusion: It is conclu ded that surgical induction of ADD in the rabbit CMJ causes enlargemen t of the condyle, which is in part caused by hyperplasia of the condyl ar cartilage.