[The effect of experimental traumatic occlusion on the mandibular condyle in rats]

The purpose of the present study was to investigate histologically and histometrically the effect of experimental unilateral traumatic occlusion (right side) on the mandibular condyle in rats. 1. Histological findings of the periodontal tissues. i. Group A (Control Group) Periodontal tissues of the right mandibular first molar: Throughout the entire experimental period, a normal structure was observed. ii. Group B (1 mm Group) Periodontal tissues of the right mandibular first molar: At 1 and 2 weeks, resorption of the dentin and cementun, irregular arrangement of the periodontal fibers, resorption of the alveolar bone, and widening of the periodontal space were observed. At 3 and 4 weeks, these changes were gradually repaired. At 8 weeks, the changes were almost repaired except the change of the alveolar bone. Periodontal tissues of the left mandibular first molar: Throughout the entire experimental period, no changes were found. iii. Group C (2 mm Group) Periodontal tissues of the right mandibular first molar: At 1 and 2 weeks, resorption of the dentin and cementum, irregular arrangement of the periodontal fibers, necrosis of the periodontal ligament, resorption of the alveolar bone, and widening of the periodontal space were observed. These changes were more marked than those of the same molar in Group B. From 3 to 8 weeks, the changes were similar to those of the same molar in Group B. Periodontal tissues of the left mandibular first molar: Throughout the entire experimental period, no changes were found. 2. Histological and histometrical findings of the mandibular condyles. i. Group B (1 mm Group) Right mandibular condyle: The layers of differentiation and hypertrophy showed a marked decrease in thickness and cellularity at 4 and 8 weeks. The layer of cartilage decreased significantly in thickness at 4 and 8 weeks (p less than 0.01). The cancellous bone showed a marked widening of bone marrow spaces at 4 and 8 weeks. It also decreased significantly in volumetric density at 4 and 8 weeks (p less than 0.01 or p less than 0.05). Left mandibular condyle: The layers of differentiation and hypertrophy showed a marked decrease in thickness and cellularity at 4 and 8 weeks. The layer of cartilage decreased significantly in thickness at 4 and 8 weeks (p less than 0.01). ii. Group C (2 mm Group) Right mandibular condyle: The layer of articular surface showed a marked decrease in cellularity at 1, 2, 3 and 8 weeks. It also decreased significantly in thickness at 1, 2, 3 and 8 weeks (p less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)