## 4 Discussion  
There have been many studies on stability after orthognathic surgery [7, 8]. However, there are no studies to identify the characteristics of patients who underwent orthognathic surgery after preoperative orthodontic surgery with clear aligners. There have been few reports of patients who underwent orthognathic surgery with preoperative correction with clear aligners. For example, when searching for \"\"clear aligner$\" and \"orthognathic$\" in PubMed, there were only five papers. Among these studies, two [9, 10] were on the use of a stent as a clear aligner during surgery, and one [11] was on the surgery-first technique. A similar search on PubMed for \"\"invisalign$\" and \"orthognathic$\" only yielded four papers. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Clear Aligners (\(\boldsymbol{r}\) = 5)**} & \multicolumn{2}{c}{**Braces (\(\boldsymbol{r}\) = 10)**} & \multirow{2}{*}{\(\boldsymbol{p}\)**-Value ***} \\ \cline{2-2} \cline{5-6}  & **Mean** & **SD** & **Mean** & **SD** & \\ \hline Preoperative orthodontic & \multirow{2}{*}{11.6} & \multirow{2}{*}{3.01} & \multirow{2}{*}{15.4} & \multirow{2}{*}{7.86} & \multirow{2}{*}{0.206} \\ treatment period (month) & & & & & \\ \hline Extracted premolar teeth (ea.) & 0.4 & 0.8 & 1.6 & 1.50 & 0.206 \\ \hline Impacted teeth (ea.) & 0 & 0 & 0.8 & 1.32 & 0.371 \\ \hline \hline \end{tabular}  
* [PERSON]’s exact test. If \(p\)-value < 0.05, there is a significant difference between the two groups.  
\end{table} 
Table 2: Preoperative orthodontic period, number of premolar extraction teeth, and number of impacted teeth between clear aligner group and traditional fixed appliance (e.g., bracket) group. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Clear Aligners (\(\boldsymbol{r}\) = 5)**} & \multicolumn{2}{c}{**Braces (\(\boldsymbol{r}\) = 10)**} & \multirow{2}{*}{\(\boldsymbol{p}\)**-Value ***} \\ \cline{2-2} \cline{5-6} \(\triangle\)**T2-T1** & **Mean** & **SD** & **Mean** & **SD** & \\ \hline L1 to NB & 0.29 & 0.75 & 0.07 & 1.46 & 0.690 \\ \hline Pog. to NB & \(-\)0.26 & 1.03 & \(-\)0.12 & 0.77 & 0.440 \\ \hline A-Pog. & \(-\)0.52 & 1.51 & 0.41 & 1.74 & 0.310 \\ \hline AFC & \(-\)2.18 & 1.70 & \(-\)0.92 & 1.50 & 0.440 \\ \hline SN Vr. & 2.68 & 1.31 & 2.00 & 4.90 & 1 \\ \hline
0-Med. & 2.21 & 2.47 & 3.74 & 7.98 & 0.768 \\ \hline \hline \end{tabular}  
* T1: 2 nd day after surgery, T2: 6 th month after surgery.
* Mann—Whitney test. \(p\)-value < 0.05 indicates a significant difference between the two groups.  
\end{table} 
Table 3: Postoperative stability measurement between the clear aligner group and the traditional fixed appliance (e.g., bracket) group on the 2 nd day and 6 th month postoperatively. According to the results of the study, the number of extracted premolars was fewer in the group that received preoperative orthodontic treatment with clear aligners compared to the group that had been corrected preoperatively with conventional orthodontic devices. There was no significant difference in the period of orthodontic treatment. Referring to Table 4, the average mandibular setback amount of the patients in the clear aligners group was 7.9 mm, which showed that preoperative orthodontic treatment with clear aligners was possible even during orthognathic surgery with a relatively large setback. For maxillomandibular fixation using elastics after orthognathic surgery in our hospital, from immediately after surgery to one week after surgery, it is not possible to open the mouth at all while occluded with 4.6 mm (170.1 g) elastic. Up to one month, it is possible to open the mouth with a 9.5 mm (170.1 g) elastic. This protocol was equally applied to all patients participating in this study, and there were no differences between the clear aligner group and the traditional orthodontic device group in elastic guide postoperatively.