# Three-Dimensional Change of Lip after Two-Jaw Surgery in Facial Asymmetry Using Facial Scanner
## 4 Discussion  
The purpose of the present study was to evaluate the 3D changes in lip asymmetry after two-jaw surgery in patients with facial asymmetry using FS and three-dimensional CT. We found that, in the transverse axes, most hard tissue landmarks, especially those related to the mandible (Mf-D, Mf-ND, and Me), and the soft tissue landmarks Ch-D and Li moved toward significantly improving asymmetry after surgery (Figure 4 and Table 3); that the anteroposterior movements of the landmarks related to the mandible (MfY-ND and MeY) and the \(\Delta\)U6Y-D correlated with the \(\Delta\)ChZ-D/ND; and in the vertical axis, the \(\Delta\)ChZ-ND showed significant correlations with the \(\Delta\)U3Z-ND and \(\Delta\)U6Z-ND (Tables 6 and 7). These results demonstrated that lip asymmetry can be improved by two-jaw surgery, and the null hypothesis was rejected. To evaluate the changes in the hard tissue after orthodontic surgery, several researchers have analyzed the changes in the landmarks on teeth or orthodontic brackets by superimposing CT images [6; 7; 8; 10; 13; 22]. Some of these studies used CT images taken six months after surgery to evaluate the changes in both hard and soft tissues [10; 13; 22]. In general, post-surgical orthodontic treatment begins 2-6 weeks after surgery; therefore, the changes in these landmarks could also be affected by orthodontic treatment. According to our protocol, the evaluation of post-operative hard tissue stabilization began 4 weeks after orthognathic surgery, and facial scanning was performed to evaluate soft tissue changes in consideration of individual differences in each patient. Several studies reported that facial morphology recovers to approximately 83-90% within 3 months following surgery [23; 24], although many studies suggest that the soft tissues stabilize 6 months after surgery [25]. The timing of the soft tissue evaluation remains controversial. In this study, we intended to evaluate the changes in the hard tissue landmarks by orthognathic surgery rather than the change caused by orthodontic treatment. For this reason, the amount of change in the hard tissue was evaluated using CT images at least one month (mean 2.0 \(\pm\) 0.9 months) after surgery, and the amount of change in the soft tissue was evaluated using FS images approximately three months (mean 3.1 \(\pm\) 0.9 months) after surgery. To reduce patient radiation exposure, it is recommended to avoid using CT on patients to obtain data that can be provided by alternate non-ionizing modalities [26]; therefore, this method using CT and FS can be utilized to evaluate hard and soft tissues before and after orthognathic surgery. Lip asymmetry in patients with facial asymmetry appears as a 3D distortion in the shape of the lips. However, the evaluation of changes in the lips after orthognathic surgery has mainly focused on the correction of the lip cart [6; 8; 22]. In this study, we analyzed the lip planes in the coronal, sagittal, and axial views to evaluate the 3D changes in the lips. Regarding changes in the coronal plane of the lip, as Ch-D moved toward the MSP, the difference in the distance from the MSP to the Ch-D and Ch-ND significantly decreased post-surgery, which is consistent with the findings of [PERSON] et al. [8]. As a result of these differential movements of Ch-D/ND, the lip width was reduced, which is consistent with