Feasibility Study For BSSRO-postoperative Rapid Orthodontic Treatment For Mandibular Prognathism

Aims:The study aims to explore the relapse of bilateral sagittal split ramus osteotomy (BSSRO) (internal fixation by rigid methods)-postoperative rapid orthodontics therapy for mandibular prognathism (MP) and the factors contributed to the relapse. To explore the changes of the temporomandibular joint (TMJ) position after operation and then compared with the traditional therapy in order to provide a theoretical basis for clinical application and improvement.Methods:From January 2012 to October 2014,18 MP patients (9 male and 9 female) who underwent the operation in Cranio-maxillo-facial Surgery Department 2, Plastic Surgery Hospital were involved in this study. BSSRO-postoperative rapid orthodontics therapy was performed without preoperative orthodontics therapy and lateral cephalometric radiographs were taken before surgery (TO), five days after surgery (T1) and one year after surgery (T2). The landmarks were measured by the software MedCeph 4.0.1.x. The subjects of TMJ study consisted of 24 MP patients (8 male and 16 female) diagnosed with MP with and without asymmetry. They were divided into 2 groups (12 symmetric patients and 12 asymmetric patients). TMJ space, condylar and ramus angle were assessed by computed tomography (CT) preoperatively (TO) and postoperatively (T2) and then compared with the traditional therapy (according to the article pubilished by the Japanese scholar Ueki. et al.). Data were analyzed by SPSS 17.0.Results:The 18 MP patients were satisfied after the BSSRO-postoperative rapid orthodontics therapy without any complications. The mean surgical setback was 7.5mm at B point and 6.6mm at pogonion. The mean long-term horizontal relapse was 2.1mm (28.0%) at B point and 2.9mm (43.9%) at pogonion. The mean vertical surgical changes showed downward displacement of B point (1.3mm) and pogonion (1.0mm). The mean long-term vertical relapse was 0.1mm at B point and 0.3mm at pogonion. The mean increase was 4.3°at ramus angle and the long-term relapse was 1.1° (25.6%). The magnitude of the surgical movement of B point, pogonion and ramus angle didn’t correlate with skeletal relapse (P> 0.05).The analysis of the 24 MP patients’CT indicated that preoperatively, there was no significant difference on the position of the TMJ between deviation and non-deviation side in symmetry group (P> 0.05) and the sagittal ramus angle in deviation side was smaller compared with non-deviation side (P= 0.023) in asymmetry group; coronal ramus angle on the non-deviation side in the symmetry group was significantly larger than that in the asymmetry group (P= 0.0161). The postoperative coronal condylar angle and anterior joint space was significantly larger than the preoperative value on non-deviation side in symmetry group (P= 0.0355 and 0.0412, respectively). The postoperative coronal ramus angle and saggital ramus angle were larger while the superior joint space was smaller than the preoperative value on non-deviation side in asymmetry group (P= 0.0175,0.0398 and 0.0319, respectively). There was no significant difference on changes of the TMJ position between the deviation and non-deviation sides both in symmetry group and asymmetry group (P> 0.05).In symmetry group, the change of posterior joint space was smaller in BSSRO-postoperative rapid orthodontics therapy group while compared with the traditional therapy group both on deviation and non-deviation sides (P= 0.007 and 0.037, respectively). In asymmetry group, there was no significant difference on deviation side between the two groups, but the change of superior joint space in BSSRO-postoperative rapid orthodontics therapy group was larger than the traditional one on non-deviation side (P= 0.020).Conclusion:These results suggestted that the skeletal relapse existed in BSSRO-postoperative rapid orthodontics therapy for MP and there was no linear correlation between the surgical movement of B point, pogonion and ramus angle and skeletal relapse. Preoperatively, the TMJ position showed similar on deviation and non-deviation sides in symmetry group while the saggital ramus angle was smaller on deciation side than non-deviation side in asymmetry group. The coronal ramus angle was larger in symmetry group than in asymmetry group on non-deviation side. Postoperatively, there was significant expansion of coronal condylar angle and anterior joint space could occur on the non-deviation side in symmetry group. In asymmetry group, the coronal ramus angle and saggital ramus angle were enlarged and the superior joint space was reduced, although the condylar position was not changed on deviation side in either group. The changes of the TMJ position were similar in diviaton side and non-deviation side in both groups. Compared with the traditional therapy, the change of posterior joint space was smaller in BSSRO-postoperative rapid orthodontics therapy both on deviation and non-deviation side in symmetry group and the change of superior joint space was larger on non-deviation side in asymmetry group.