The form of facial asymmetry was traditionally analyzed using PA cephaloradiographs [22,23,24,25]. In such reports, the frequency of facial asymmetry among patients with facial deformities showed a 21–67% distribution. Severt and Proffit  reviewed the medical records of 1460 patients with maxillofacial deformities and reported that 34% of them showed facial asymmetry, with a high prevalence of facial asymmetry (40%) in patients with class III malocclusion. Tani et al.  analyzed the PA cephaloradiographs of 239 patients with maxillofacial deformities and reported that 28% of them also had facial asymmetry.
During the treatment of patients with facial asymmetry, preoperative orthodontic treatment is first provided to remove the dental compensation of the maxillary and mandibular dentition. The midline of the anterior teeth is aligned with the midline of the jaws, and the inclinations of the anterior teeth and the occlusal plane are matched. This increases the predictability of postoperative teeth movement and simplifies the surgical planning . Also, by matching the left and right posterior torques and increasing the overjet of the non-involved canines, asymmetry worsening is prevented by occlusal interference during surgery . Then, through orthognathic surgery, the midline of the jaw and that of the anterior are aligned. Complete decompensation may not be achieved, however, due to the function of occlusion, the direction of natural compensation, and the strength of the muscles. This can result in difficulties in orthognathic surgery and postoperative orthodontic treatment.
Treating patients with facial asymmetry poses more difficulties than treating those without. If the vertical difference between the first molars of the left and right maxilla with respect to the FH plane is not accurately assessed in preoperative orthodontic treatment, or if the height difference between the left and right mandibular occlusal planes with respect to the mandibular plane is not accurately assessed and only mandibular surgery is performed, the asymmetry cannot be completely corrected . If the cross-decompensation of dentition in preoperative orthodontic treatment is incomplete, postoperative skeletal asymmetry will remain even after achieving satisfactory occlusion through surgery. Also, an asymmetric maxillary arch may appear in the posterior maxilla despite carefully performed preoperative orthodontic treatment; as a result, asymmetry may remain in the mandibular angle and ramus mandibulae due to an inappropriately positioned mandible .
Several studies have been reported on the overall trend of relapse after facial asymmetry surgery. In 1997, Severt and Proffit  reported a 40% regression rate after orthognathic surgery. In 2002, Lai et al.  reported that menton lateral relapse occurred in up to 24% of the cases. It was reported that the cause of this was the difference between the amount of mandibular retraction in the left and right sides and the displacement of the mandibular condyle. In 2009, however, Ko et al.  reported symmetric results and skeletal stability of the chin after orthognathic surgery.
Many studies on the surgery-first approach have been reported of late. Compared with the traditionally used method, the surgery-first approach has many advantages, such as increased patient cooperation, efficient decompensation, and decreased treatment duration . In 2011, Liou et al.  presented a guideline for model surgery and orthodontic treatment during the implementation of the surgery-first approach . In 2011, Hwang et al.  reported that horizontal and vertical skeletal stability can be achieved after orthognathic surgery through the surgery-first approach in patients with class III skeletal malocclusion. Thus, most of the published papers are on the class III skeletal malocclusion [15,16,17,18, 31, 33, 34], and there is no paper as yet on asymmetry.
In this study, statistically significant changes were observed in U1-SRP, R body height, and L body height during the T1–T2 period when orthognathic surgery through the surgery-first approach was performed, and statistically significant changes were observed in R body height and L body height during the T1–T2 period when the traditional method was used. These results suggest that orthognathic surgery through the surgery-first approach provides a degree of skeletal stability comparable to that provided by the traditional method and that both the treatment and control groups in this study retained skeletal stability postoperatively for 6 months. In this study, the mean duration of the treatment period for orthognathic surgery through the surgery-first approach was 15.9 months whereas the mean treatment period for the cases without the surgery-first approach was 32.9 months. Thus, the surgery-first approach cases showed a shorter treatment period than the traditional method cases. In 2011, Hwang et al. reported that in class III malocclusion patients, horizontal and vertical bone stability was obtained after orthognathic surgery through the surgery-first approach .
In the case of patients with asymmetry, surgery is performed by setting the anterior midline to predict the change in the dental axis of the anterior and posterior maxilla and mandible owing to the postoperative compensation, and orthodontic treatment is provided after surgery. In those cases where orthognathic surgery was performed using the surgery-first approach, statistically significant differences were observed in U1-SRP during the T1–T2 period. Such results may be due to the crowding of the anterior teeth, the dental spacing, and the deviation of the dental axis from the basal bone. When performing preoperative orthodontic treatment, the orthodontist will decompensate the teeth to the basal bone. For these reasons, it is important to set up the occlusion and the setting of the maxillary incisors in the preoperative planning through the surgery-first approach. The posterior teeth axis is also one of the factors that make it difficult to set the occlusion in the surgery-first approach.
The subjects of this study were limited to patients who did not have severe preoperative lateral posterior dental compensation and those who did not have posterior cross-bite. Also, a stent was worn for up to 10 weeks to resolve the unstable occlusion in the posterior after surgery, and when necessary, the surgical stent was fixed at the anterior maxilla after cutting out the posterior section of the first premolars, to address the transverse disharmony in the posterior maxilla and mandible using the cross elastics of the posterior. As mentioned earlier, clinical difficulties were observed in postoperative orthodontic treatment, but it is believed that these were not statistically significant.