Condylar changes following vertical subsigmoid osteotomy in different setback magnitude

Abstract

Objectives: This retrospective study aims to compare the effect of different mandibular setback amount by vertical subsigmoid osteotomy (VSSO) on the pattern of condylar remodelling in both metric and morphologic analysis at 1 year post surgery.

Materials and Methods: 200 patients diagnosed of mandibular prognathism and had undergone VSSO with various setback amounts from 2007 until 2012 at the Prince Philip Dental Hospital were included in this study. Presurgical and 1 year post surgical Postero-Anterior Cephalogram, Lateral Cephalograms and Cone Beam Computed Tomography (CBCT) Scans were retrieved. Tracings of plain cephalometric radiographs were performed. CBCT data sets were used to create 3D condyles to measure the linear and condylar axis angle value in multiplanar view. Finally the pre and postsurgical 3D condyle-ramus units were superimposed using stable registration point in the condylar neck and ramal area above the lingual to assess the condylar bone remodelling by topographic and multiplanar slide views.

Result: From the plain radiographic tracings, there were no significant differences in the changes of ramus inclination angle, intergonial width and total ramus angle between postoperative (T2) and preoperative (T1) values across the setback groups. A gradual increase in the postoperative sagittal condylar axis angle is detected with greater setback in the CBCT multiplanar analysis while other linear and angular condylar changes were not significantly different. 3D Topography (T2 -T1) superimposition analysis of the condylar surface showed no significant relation between the remodelling changes and the setback magnitude except at the superior posterior zone. Multiplanar view (T2-T1) superimposition analysis in the coronal and sagittal planes showed no significant relationship between the remodelling changes and the setback magnitude. However there was higher proportion of positive remodelling following higher setback amount at the midanterior and posteromedial zone in the axial plane.

Conclusion: Condyle remodelling is noted to be positive and not detrimental following VSSO. The positive remodelling effect remains stable regardless of the amount of VSSO setback.