## 4 Discussion  
Many studies have reported sagittal and vertical postoperative stability of BSSRO with significant variability ranging from 1.0% to 91.3% [7, 8, 9, 10, 11]. The risk factors of postoperative relapse include the amount of setback [12, 13], change in the gonal angle [14, 15], rotation of the proximal segment [16, 17], stability of the distal segment [18], change in the condylar long axis [13], retention of fixation [14], and stretching and alteration of the ptergo-masseteric sling [19]. The amount of mandibular setback is \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**IGW** & **T1** & **T2** & **T3** & **T2-T1** & **T3-T2** & **T3-T1** \\
**Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** \\ \hline GI & 110.37 \(\pm\) 6.80 & 111.45 \(\pm\) 7.92 & 109.91 \(\pm\) 7.57 & 1.08 \(\pm\) 6.42 & \(-\)1.54 \(\pm\) 1.65 & \(-\)0.46 \(\pm\) 5.62 \\ GII & 112.20 \(\pm\) 5.21 & 112.16 \(\pm\) 8.17 & 100.84 \(\pm\) 33.80 & \(-\)0.04 \(\pm\) 6.71 & \(-\)11.32 \(\pm\) 29.68 & \(-\)11.36 \(\pm\) 34.54 \\ GIII & 110.80 \(\pm\) 4.77 & 110.18 \(\pm\) 5.37 & 109.44 \(\pm\) 5.29 & \(-\)0.62 \(\pm\) 2.85 & \(-\)0.74 \(\pm\) 2.60 & \(-\)1.36 \(\pm\) 1.98 \\ \hline F(p) & 0.295 (0.747) & 0.246 (0.783) & 0.696 (0.507) & 0.266 (0.768) & 1.319 (0.283) & 0.972 (0.390) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Changes in interamandibular intergonal width (IGW) according to amount of mandibular setback. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Gonial Angle** & **T1** & **T2** & **T3** & **T2-T1** & **T3-T2** & **T3-T1** \\
**Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** \\ \hline GI & 128.25 \(\pm\) 4.40 & 128.68 \(\pm\) 5.71 & 129.60 \(\pm\) 4.52 & 0.37 \(\pm\) 6.02 & 0.98 \(\pm\) 4.02 & 1.35 \(\pm\) 4.39 \\ GII & 128.41 \(\pm\) 4.10 & 129.49 \(\pm\) 4.12 & 130.00 \(\pm\) 4.19 & 1.07 \(\pm\) 3.04 & 0.51 \(\pm\) 3.76 & 1.59 \(\pm\) 4.84 \\ GIII & 132.06 \(\pm\) 5.49 & 131.41 \(\pm\) 7.57 & 132.71 \(\pm\) 6.04 & \(-\)0.64 \(\pm\) 5.27 & 1.30 \(\pm\) 4.16 & 0.66 \(\pm\) 4.18 \\ \hline F(p) & 2.329 (0.115) & 0.585 (0564) & 1.245 (0.303) & 0.369 (0.685) & 0.112 (0.895) & 0.142 (0.868) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Changes in gonal angle according to amount of mandibular setback. usually considered the single most important factor that affects relapse following BSSRO or IVRO. The practical significance of the trimming and removal of the posterior part of the mandible aims at reducing inter-segmental interferences, thus improving the patient's facial appearance through muscle atrophy or by volume reduction through the remodeling process as reported in previous studies [20; 21; 22]. Many authors have addressed the issue that both degrees of downward and forward movements of the condyle in the IVRO are greater than those in the BSSRO [19; 23]. [PERSON] et al. [18] reported that after both surgical procedures, namely the BSSRO and IVRO, the increase in the transverse or frontal ramus angle was significantly related to the rotation of the distal segment during the remodeling phase. Therefore, lateral and frontal differences between the proximal and distal segments are commonly found between BSSRO and IVRO during the bony remodeling process. In particular, when the distal segment is set back further, it can push the proximal segment more laterally. Therefore, a larger than expected frontal gap can occur. Since patients with mandibular protrusion generally have a prominent mandibular angle, mandibular setback surgery without considering the mandibular angle potentially reduces the aesthetic satisfaction of the patient. The condyle head tended to move downwards, rotating inward in the axial view and backward by a statistically significant amount in the sagittal view. [PERSON] et al.