Experimentally created nonbalanced occlusion effects on the thickness of the temporomandibular joint disc in rats

To test the hypothesis that experimentally created physiologically nonbalanced occlusion will not affect the thickness of the temporomandibular joint (TMJ) discs in rats. Twenty-four 8-week-old Sprague-Dawley rats were equally divided into a control group that was left untreated and an experimental group where a nonbalanced occlusion was created. Elastic rubber bands, 1 mm in diameter, were inserted and 1 week later were replaced by plastic material between the first and the second molars of the left maxillary and the right mandibular dentitions to move the first molars about 0.8 mm mesially. This created and maintained a physiologically nonbalanced occlusion. The animals were euthanized 8 weeks later, and the TMJ disc thickness was measured on histologically prepared slices using an electronic meter. Two-way univariate analysis of variance was used to compare the groups (alpha level = .05). The intermediate zone was thicker in the experimental group than in the control group (P = .003), but no differences were found between groups regarding the anterior and posterior bands. There were no significant sex-related effects on this observation. The hypothesis is rejected. The results indicate that the intermediate zone of rat TMJ disc has the ability to adapt to the alteration of the space between condyle and fossa caused by occlusion changes. Further studies on larger groups that are followed for longer times are needed.