CHANGES IN MANDIBULAR ROTATION AFTER MUSCULAR RESECTION - EXPERIMENTAL-STUDY IN RATS

The purpose of this study was to evaluate the effect of bilateral musc ular resection on the rotational pattern of the rat mandible. The spec ific aim of the study was to seek possible changes in ''articular grow th'' in the posterior (ramus and condyle of the mandible), and in the anterior part of the face (upper viscerocranium, and maxillary and man dibular dentoalveolar processes), The masseter, temporal, and suprahyo id muscles were bilaterally resected in three experimental groups of 2 1-day-old female Wistar rats, Another group of rats served as control. The results were evaluated at 42 (prepubertal) and 60 days after birt h (pubertal rats). The craniofacial growth pattern, ramus dimension, c ondylar growth direction, histologic evaluation of condylar cartilage, and dentoalveolar processes height changes were studied. Two mandibul ar rotational patterns were found: one inferior after masseter muscles resection (MR), and the other superior after temporal muscles resecti on (TR), A less intense superior rotational pattern, after suprahyoid muscles resection (SR), was found also, Morphologic changes were more intense in older rats. On the contrary, more intense condylar histolog ic changes were found in younger rats, Changes in ''articular growth'' primarily take place at maxillary and mandibular dentoalveolar proces ses. Condylar growth amount could be modified to a limited extent. Mor e important were the changes in condylar growth direction. An upward r otational pattern of the upper viscerocranium was detected when the in ferior mandibular rotation pattern was produced.