Changes in mandibular rotation after muscular resection. Experimental study in rats.

The purpose of this study was to evaluate the effect of bilateral muscular resection on the rotational pattern of the rat mandible. The specific aim of the study was to seek possible changes in "articular growth" in the posterior (ramus and condyle of the mandible), and in the anterior part of the face (upper viscerocranium, and maxillary and mandibular dentoalveolar processes). The masseter, temporal, and suprahyoid muscles were bilaterally resected in three experimental groups of 21-day-old female Wistar rats. Another group of rats served as control. The results were evaluated at 42 (prepubertal) and 60 days after birth (pubertal rats). The craniofacial growth pattern, ramus dimension, condylar growth direction, histologic evaluation of condylar cartilage, and dentoalveolar processes height changes were studied. Two mandibular rotational patterns were found: one inferior after masseter muscles resection (MR), and the other superior after temporal muscles resection (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 histologic changes were found in younger rats. Changes in "articular growth" primarily take place at maxillary and mandibular dentoalveolar processes. Condylar growth amount could be modified to a limited extent. More important were the changes in condylar growth direction. An upward rotational pattern of the upper viscerocranium was detected when the inferior mandibular rotation pattern was produced.