Effects of a mandibular lateral shift on the condyle and mandibular bone in growing rats

Objective: To examine the effects of mandibular lateral shift on the growth and morphology of the condyle and mandibular bone in growing rats. Materials and Methods: A maxillary resin plate was designed to displace 4-week-old rat mandibles 2 mm to the left during closure. The plate was cemented, and the rats were killed after 2, 4, 8, or 12 weeks. Gross dimensions of the condylar head were measured. Radiographic films of the mandibles were exposed, and selected measurements were made. The newly formed bone in the condyle was evaluated with periodic acid and Schiff's reagent (PAS) staining. Results: The length of the condylar head was greater on the ipsilateral side compared with the contralateral side. The experimental rats developed an asymmetric mandible, shorter in horizontal dimension but longer in the vertical dimension on the ipsilateral side. The mandibular growth direction was also affected, with the mandible on the ipsilateral side growing in a more anterior and superior direction. The amount of newly formed bone was greater in the superior subchondral region but lower in the posterior subchondral region on the ipsilateral side compared with the contralateral side. Conclusions: Mechanical stimuli delivered by a functional shift produce a series of morphological and histological responses in the condyle and lead to condylar and mandibular asymmetry in rats.