Abstract:

Abstract:Objective To elucidate the relationship between mandibular lateral displacement and mandible asymmetry by observing the morphological changes of condylar head and mandible during mandibular lateral displacement in growing rats. Methods Forty-eight male Wistar rats at the age of four weeks were divided at random into experimental and control groups, with 24 rats in each group. A super-hard resin plate was cemented to upper incisors to displace rat mandibles 2 mm to the left during closure (Ipsilateral side). A metal crown was fitted to lower incisors. The rats were killed 2, 4, 8 or 12 weeks after appliance attachment. The mandible was dissected out and halved. The length and width of condylar head were measured with a caliper. Radiographic films of the mandibles were exposed, and selected measurements were made.
Results The length of condylar cartilage on the ipsilateral side was significantly larger than contralateral side in experimental group(P<0.05), while there was no significant difference between two sides for the width of condylar cartilage. The experimental rats developed an asymmetric mandible, significantly shorter in horizontal dimension but longer in the vertical dimension on the ipsilateral side(P<0.05). The growth direction of mandible was also affected in experimental group with a more forward and upward growth on ipsilateral side. Conclusion The different shape of condylar cartilage and growth direction of mandible induced by mandibular lateral displacement on bilateral sides can be ascribed to the asymmetry of mandibular bone on two sides.

Key words: condylar cartilage, mandible; , lateral displacement, morphology