Three-dimensional changes in condylar position in skeletal class Ⅲ patients with mandibular deviation after bilateral sagittal split ramus osteotomy

Abstract

Objective: To investigage the three-dimensional changes in condylar position after bilateral sagittal split ramus osteotomy (BSSRO) in skeletal class Ⅲpatients with mandibular deviation using cone-beam CT (CBCT). Methods: Twenty-five skeletal class Ⅲ patients with mandibular deviation were included. The patients (12 males and 13 females, aged 19-25 years, average age 22.4 years) were treated in the Department of Orthodontics, Affiliated Stomatological Hospital, Nanchang University from October 2013 to March 2017. The patients were divided into T1, T2 and T3 groups (T1 group: CBCT taken within 1 week before operation; T2 group: CBCT taken within 1 week after operation; T3 group: CBCT taken 6-8 months after surgery). Three sets of image data of condyles on both sides (deviation side and contralateral side) were obtained. After the DICOM data collection, the software of Mimics 17.0 was used to perform three-dimensional reconstruction and condylar position measurements: the distance from the condylar top (CoT) to the standard horizontal plane (SHP), the middle sagittal plane (MSP) and the sella coronal plane (SCP) (CoT-SHP, CoT-MSP, CoT-SCP); the distance from the condylar center (CoC) to SHP, MSP and SCP (CoC-SHP, CoC-MSP, CoC-SCP); the angle from the condyle cella plane (CCP) to SHP, MSP and SCP (CCP-SHP, CCP-MSP, CCP-SCP); the angle from the condyle sagittal plane (CSP) to SHP, MSP and SCP (CSP-SHP, CSP-MSP, CSP-SCP) and the distance of the anterior, superior, posterior, medial, central and lateral joint space. One-way ANOVA and LSD-t test were used to compare the changes in condylar position at different periods (T1, T2, and T3). Results: Within 1 week before operation on the deviation side, CoT-SHP [(2.5±1.3) mm], CSP-MSP (41.2°±8.4°) and the posterior joint space [(2.0±0.6) mm] were obviously increased (P<0.05), and CoT-SCP [(9.1±3.3) mm], CCP-MSP (78.2°±5.2°) were decreased significantly (P<0.05); on the contralateral side, CoT-MSP [(50.4±3.1) mm], CCP-MSP (80.6°±6.0°), the anterior joint space [(2.2±0.6) mm] and the medial joint space [(2.6±0.6) mm] were obviously increased (P<0.05), and CCP-SCP (11.4°±8.8°) were decreased significantly (P<0.05). Six to eight months after surgery, CoT-SHP [(2.2±1.0) mm] and the posterior joint space [(1.9±0.5) mm] on deviation side and CoT-SCP [(8.4±2.8) mm] on the contralateral side were increased significantly (P<0.05). No significant difference was found in other measurements (P>0.05). Conclusions: The condylar position in skeletal class Ⅲ patients with mandibular deviation was asymmetrical. Within 1 week after the operation of BSSRO, the condyle on the deviation side was moved forward, downward and inward. Meanwhile, the condyle on the contralateral side was moved backward and outward. Six to eight months after surgery, the condylar position on both sides was gradually restored to the pre-operative condylar position.