Effect of the magnitude of condylar head displacement on the TMJ function in skeletal class II patients undergoing different degrees of mandibular advancement: A retrospective comparative study

This study aimed to compare the condylar head displacement (CHD) after bilateral sagittal split ramus osteotomy (BSSO) between different degrees of mandibular advancement in skeletal class II patients and to evaluate whether the temporomandibular joint (TMJ) function would be affected.Fifty-nine patients (118 condyles) were included in this retrospective study and were divided into three groups based on the distance of mandibular advancement. The CHD in three directions, x (sagittal direction), y (coronal direction), and z (axial direction), was measured before operation (T0), immediately after operation (T1), and at least 6 months after operation (T2), and the TMJ function of patients was followed up and scored using the Helkimo index system. All the abovementioned data were statistically analyzed, and p < 0.05 was considered the statistical difference standard.During the BSSO surgery, the condyle was predominantly displaced in a lateral, posterior, and superior direction whenever in T1 and T2, even though the degree of CHD was different. Regarding the amount of CHD, the large advancement group was higher than the other two groups in T1 and T2 (p＜0.01). The Helkimo index scores of the three groups were evaluated, and there was no significant statistical difference between the Ai and Di index of the three groups.In our center, CHD occurred in lateral, posterior, and superior directions following mandibular advancement in skeletal class II patients, with a positive correlation between the CHD and the mandibular advancement; however, the TMJ function of the three groups did not show significant differences.