Comparison of condylar morphology changes and position stability following unilateral and bilateral sagittal split mandibular ramus osteotomy in patients with mandibular prognathism

Abstract

Background Unilateral sagittal split ramus osteotomy (USSRO) is not widely used given the postoperative instability caused by the inevitable rotation of the mandibular segment during surgery. However, the influence of mandibular movement on the condylar morphology and position stability has not been completely explored. The aim of the study was to quantitatively evaluate the effect of USSRO on the condylar surface morphology changes and postoperative stability in patients with mandibular lateral prognathism and compare these findings with the classic bilateral sagittal split ramus osteotomy (BSSRO). Patients/methods This was a retrospective study involving 134 patients with mandibular lateral prognathism who received USSRO ( n = 56) and BSSRO ( n = 78) surgery. Here, cone beam computed tomography (CBCT) was performed before surgery (T0), immediately after surgery (T1), and 1 year postoperatively (T2). Differences of condylar sizes, condylar surface deviation, and mandibular positioning parameters (dental midline deviation, SNB, SN-MP) were calculated from T0 to T2. Comparisons were performed at the deviated side or nondeviated side of condyles between the USSRO and BSSRO groups. The relation between the dental midline deviation and condylar surface morphology changes from T0 to T2 were investigated. Results Condylar surface morphology changes at the deviated side of temporomandibular joint (TMJ) before and 1 year after the surgery were significantly different between the USSRO and BSSRO groups. The dental midline deviation was related to the changes of condylar volume, surface size and surface deviation at the deviated side of TMJ in patients following USSRO. No significant difference was noted between the USSRO and BSSRO groups for postoperative condylar surface morphology changes at the nondeviated side. In both groups, significant differences between T0 and T1 and no significant difference between T1 and T2 were noted for all of the mandibular positioning parameters. Conclusions Both BSSRO and USSRO exhibit favorable postoperative stability in the correction of mandibular prognathism. After USSRO surgery, condylar surface changes occurred at the deviated side of the TMJ, and the dental midline deviation was closely related to the changes of condylar surface morphology. USSRO represents a stable alternative for minor asymmetric mandibular prognathism correction with the advantages of reduced operating time and surgical trauma.

The Evaluation of Condylar Position Change in the Asymmetric Mandible Following Sagittal Split Osteotomy

“…Mandibular morphology, such as mandibular flaring and length, and surgical technique influence the amount of bony interference. 19,20 Ueki et al 21 suggested using a bent titanium plate. Kang et al 18 applied a bone graft in the area of the anterior gap to prevent torque on condyles.…”

“…In contrast, a posterior gap in the non-deviated side may lead to medially condylar displacement while using bicortical screws or forcefully closing the gap. Mandibular morphology, such as mandibular flaring and length, and surgical technique influence the amount of bony interference 19,20 …”

Evaluation of Condylar Positional, Structural, and Volumetric Status in Class III Orthognathic Surgery Patients

“…In the maxillary single-jaw surgery group at one year after surgery, condylar volume increased, on average, by 16.7 ± 1.9 mm 3 , which represents 9.1% of the pre-operative volume. Lin et al [57] assessed condylar volumetric changes in skeletal Class III patients with an asymmetric mandibular prognathism. In the BSSO group, the average volume changes of the deviated and non-deviated sides of the condyles were 71.6 ± 11.9 and 59.3 ± 8.4 mm 3 , respectively, one year after surgery.…”