Altered mandibular function and prevention of skeletal asymmetries after unilateral condylectomy in rats

Unilateral condylar injury is known to be a frequent cause of mandibular asymmetry. Whether this is due to the trauma itself or to the disturbed function that follows the injury is a very important question with ramifications for clinical complications related to facial asymmetries. The aim of this study was to test the hypothesis that mandibular function in a protruded position can compensate for the absence of one condyle and prevent potential growth asymmetries. Forty-eight 4-week-old rats were divided into two experimental and two control groups consisting of 12 animals each, as follows: (A) unilateral condylectomy was performed on the right side and the mandible was left to function normally; (B) after unilateral condylectomy on the right side, the mandible was forced to function in a protruded position; (C) a sham operation was performed in the condylar area of the right side but no appliance was used; and (D) 12 animals were used as controls without any operation or appliance. Mandibular protraction was achieved by means of a specific appliance, acting via rubber bands, pulling the mandible in a straight, forward direction with a force of 25 g for 12 hours per day. The experimental period was 30 days. Dorsoventral radiographs were taken and vital dyes were administered at three time intervals, i.e. on days 1, 15 and 30, for all animals. Cephalometric analysis included 14 measurements. Findings resulting from statistical analysis and comparisons of measurements obtained in the four groups can be summarized as follows: (i) when comparing group A with groups C and D, less growth was found in the right mandibular sides in group A; (ii) when comparing group B and groups C and D, less growth was found in the right mandibular sides in group B; (iii) when comparing groups A and B, more growth was found in the right mandibular sides in group B; (iv) when comparing the right and left mandibular sides in group A, less growth was found in the right side; and (v) when comparing the right and left mandibular sides in group B, no significant growth differences were found. These findings support the hypothesis that altered mandibular function in a protruded position can compensate for the effects of unilateral condylectomy and prevent the appearance of skeletal mandibular asymmetries in growing rats.