Changes in mandible and masseter muscle following method of orthognathic surgery in skeletal Class III patients with facial asymmetry

Abstract

The aim of this study was to evaluate changes of gonial angle area in skeletal Class III patients with facial asymmetry following two kinds of orthognathic surgery, intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO). Using computed tomography (CT), one study was conducted on 20 skeletal Class III patients with facial asymmetry who had undergone SSRO orthognathic surgery at K University Hospital. Measurements from the reconstructed three-dimensional (3D) CT images were compared from T0 (before surgery) and T1 (1 year after surgery). Another longitudinal study was conducted on 17 skeletal Class III patients with facial asymmetry who had undergone IVRO orthognathic surgery at Y University Hospital. Measurements from the reconstructed 3D CT images were compared from T0 (before surgery), T1 (1 year after surgery), and T2 (4 years after surgery). The mandibular total volume, intergonial width, mandibular gonial angle area volume, the maximum cross-sectional area (MCSA) and angle of the masseter muscle were measured from the reconstructed 3D CT images. Using 3D CT images, we evaluated this data on the deviated side and non-deviated sides. We also compared this data between SSRO group and IVRO group. The correlation between the degree of facial asymmetry and postoperative changes of mandibular gonial angle area volume and the maximum cross-sectional area of the masseter muscle were assessed and analyzed with the following results.

1. When comparing the mandibular change, during T0-T1, a significant decrease was noted in mandibular total volume, intergonial width and mandibular gonial angle area volume of non-deviated side (P<0.01, P<0.05, P<0.01), and no significant difference was noted in mandibular gonial angle area volume of deviated side (P>0.05) in SSRO group. In IVRO group during T0-T1, a significant decrease was noted in mandibular total volume and mandibular gonial angle area volume on both the deviated and non-deviated sides (P<0.01), and no significant difference was noted in intergonial width (P>0.05). Only mandibular total volume change was noted to be greater in IVRO group (10.6%) than SSRO group (3.3%) (P<0.01). No significant differences were noted between SSRO group and IVRO group in mandibular gonial angle area volume and intergonial width (P>0.05).

2. When comparing the masseter muscle change, during T0-T1, a significant increase was noted in maximum cross-sectional area of the masseter muscle on deviated side in SSRO group (P<0.01), and no significant difference was noted on non-deviated side (P>0.05). In IVRO group during T0-T1, no significant difference was noted in maximum cross sectional area of the masseter muscle (P>0.05). No significant difference was noted between SSRO group and IVRO group in maximum cross-sectional area of the masseter muscle (P>0.05). During T0-T1, a significant decrease was noted in masseter muscle angle on non-deviated side in both SSRO group and IVRO group (P<0.05, P<0.01).

3. At T1-T2, mandibular gonial angle area volume on both the deviated and non-deviated sides was noted to be smaller as the amount of menton deviation was greater in IVRO group (P<0.01, P<0.05). There was no correlation between the amount of menton deviation and postoperative changes in maximum cross-sectional area and angle of the masseter muscle (P>0.05).

As a result of this study, there was no significant difference of the change in mandibular gonial angle area volume and maximum cross-sectional area of the masseter muscle except that the mandibular total volume change of IVRO group was larger than that of SSRO group in comparison of the change between SSRO group and IVRO group during T0-T1. It is considered that further studies including expansion of study subjects and longitudinal study of SSRO group whether comparative study results of the two surgical methods depending on the degree of facial asymmetry can affect the choice of surgical method will be necessary in the future.