Study On Magnetic Resonance Imaging Of Lateral Pterygoid Muscle And Morphology Asymmetry Of Temporomandibular Joint In Patients With Skeletal Mandible Deviation

Mandible deviation patients can have an asymmetrical face which often results from unbalanced lateral and vertical growth of the craniofacial structures. The structural asymmetry of the craniofacial complex in adults is considered to be a functional adaptation to mandibular displacement. Some studies had suggested that mandibular displacement can change the modeling process of the temporomandibular joint (TMJ) and gradually results in permanent structural asymmetry in a growing person. In addition, mandibular asymmetry does not consist of only left-right size differences between the maxilla and mandible but also shows morphological difference in the TMJ, which has been confirmed by cephalometric analysis. Before planning treatment of patients with mandibular deviation, it is necessary to understand the difference in TMJ morphology between the deviated and non-deviated sides. Facial asymmetry caused by mandibular lateral displacement is a relatively common problem in patients with internal derangements of the TMJ. Details of the morphology of TMJ and their relationship to skeletal asymmetry have not been extensively reported.The purpose of our study was designed to investigate the characteristics of lateral pterygoid muscle (LPM) and TMJ morphology in patients with skeletal mandible deviation, and the relationship between LPM's and TMJ morphology and mandibular deviation which may provide some useful references for clinical treatment. The study group included 20 skeletal mandible deviation patients from 18 to 35 years of age. Ten age-matched normal occlusion people were also measured as control subjects. The MRI was performed in mouth closed position and in maximum mouth open position.Results:(1) In mouth closed position, the superior belly of the LPM's length, thickness and area on the non-deviated side showed higher than the deviated side and control subjects (P<0.05). The inferior belly of the LPM's length, area on the non-deviated side were also larger than the deviated side (P<0.05). But there was no significant difference on thickness. In maximum mouth open position, the superior belly and inferior belly of the LPM showed the same tendency. The length and area on the non-deviated side were larger than the deviated side (P<0.05). However, there was no significant difference on thickness. (2) In the deviation group, the TMJ on the deviated side showed a significantly steeper eminence than on the non-deviated side (p<0.05). (3) Disk displacement comparisons revealed no significant differences between two sides. The anterior joint space and the posterior joint space did not differ markedly.Conclusions:The LPM of skeletal mandible deviation patients exhibited significant morphological difference between the nondeviated and deviated side. This might be the result of asymmetry of condyle position and morphology, and also could be the result of long term occlusion instability. The patients also exhibit significant morphological differences between the deviated and non-deviated TMJs concerning the slope of the articular eminence, which correspond to facial asymmetry.