Correlative Study Of Transverse Displacement Of Gonion Caused By Mandible Setback Via Bilateral Sagittal Split Osteotomy

Objective:Widening of mandibular angle is common in some patients after internal fixation of proximal and distal segments during BSSO.3D CT combined with digital software was used for three-dimensional overlap,determine the marking points and measure,and assess the transverse changes of the gonion and mandibular proximal segment in patients with mandibular protrusion deformity after BSSO,so as to provide reference for preventing the widening of mandibular angle.Methods:Ten patients with mandibular protrusion deformity,including 20 proximal segments,admitted to the Department of Oral and Maxillofacial Surgery of the Affiliated Stomatological Hospital of China Medical University from June 2019 to October 2020 were retrospectively analyzed.Whole cranial spiral CT data were collected preoperatively(T1)and one week postoperatively(T2).Proplan CMF3.0software was used to reconstruct the three-dimensional skull models before and after surgery,and matched and overlapped them.After segmentation and matching of each side of the proximal segment,the distance from each marked point on the proximal segment to the median sagittal plane was measured before and after operation.SPSS23 software was used for statistical analysis.Paired sample t-test was used to evaluate the differences in measured values before and after surgery.Results:The lateral displacement of gonion was 2.3±1.0 mm,and the change was statistically significant(P<0.05).The medial displacement of the coronoid process was 1.7±0.8 mm,and the change was statistically significant(P<0.05).There was no significant lateral displacement of condyle(P> 0.05).Conclusion:Three-dimensional model superimposition can effectively evaluate the lateral displacement of gonion during BSSO.In patients with mandibular protrusion deformity,gonion was shifted laterally and mandibular angle was widened.At the same time,the coronoid process was shifted medially,and the condyle was not shifted laterally during BSSO.In order to prevent mandibular angle widening,the proximal segment should be placed in the preoperative position as far as possible.