Purpose: The purpose of the present study was to evaluate the relationship between masticatory muscle volume and mandibular skeletal measurements in patients with and without facial asymmetry. This was done in order to determine whether asymmetric mandibular prognathism is related to masticatory muscle asymmetry.
Patients and methods: The study was conducted with 40 adult patients with mandibular prognathism composed of 2 groups, the asymmetry group (n = 20) and the nonasymmetry group (n = 20). Using 3-dimensional reformatted computed tomography (CT) images, the volume of masticatory muscle (masseter, temporal, medial, and lateral pterygoid muscles) and various skeletal measurements (hemimandibular volume, ramal height, body length, mandibular length, gonial angle) were evaluated and compared. The right-left difference was expressed by an asymmetry index {(right-left)/left, %}.
Results: The results showed that in the asymmetry group, the longer mandibular side (contralateral side of chin deviation) exhibited longer ramal and body length, a wider gonial angle, and more hemimandibular volume with less medial pterygoid volume, whereas the nonasymmetry group did not show a statistical bilateral difference between the skeletal and muscular measurements. The correlation analysis showed that patients with facial asymmetry did not have similar patterns of muscle-bone relation as compared with the symmetrical subjects.
Conclusion: In patients with mandibular prognathism, the bilateral difference in muscle volume would reflect the difference in the spatial anatomy of a skeletal structure and could not predict mandibular skeletal asymmetry.