Degenerative changes in rat condylar cartilage induced by non-matching occlusion created by scattered orthodontic teeth-moving.

The effect of occlusion on the temporomandibular joint (TMJ) is debated. By inserting rubber-bands that were replaced by self-curing resin one week later, the left maxillary and the right mandibular first-molars were moved and kept mesially in Sprague-Dawley (SD) rats in both experimental I (EXP-I) and II (EXP-II) groups, aiming to establish a non-matching cusp-to-fossa occlusal relation. Four weeks later, the left maxillary and the right mandibular third-molars were moved and kept distally in the EXP-II group. Degenerative changes, typically as a cell-free area, were observed in TMJs of the EXP groups. Binary logistical analysis indicated that the odds ratio of EXP group, EXP-II vs. EXP-I, on the incidence of a cell-free area, was 2.8 (p=.036). Time point, gender, and side did not have such effects (p>0.05). The results indicate that the persistence of more scattered non-matching cusp-to-fossa occlusion is more harmful to the condylar cartilage in terms of the incidence of degenerative changes.