Three-dimensional soft tissue effects of mandibular midline distraction and surgically assisted rapid maxillary expansion: an automatic stereophotogrammetry landmarking analysis.

Studies on mandibular midline distraction (MMD) are mostly performed using conventional research methods. Concerning surgically assisted rapid maxillary expansion (SARME), more research is conducted using three-dimensional (3D) techniques. Research on bimaxillary expansion, the combination of MMD and SARME, is reported sparsely. The main objective of this study was to provide a 3D evaluation of soft tissue effects following SARME and/or MMD. Patients who underwent SARME and/or MMD between 2008 and 2013 were included. Stereophotogrammetry was undertaken at the following time points: preoperative (T1), immediately post-distraction (T2), 1year postoperative (T3). An automatic 3D facial landmarking algorithm using two-dimensional Gabor wavelets was applied for the analysis. Twenty patients who had undergone SARME were included, 12 of whom had undergone bimaxillary expansion. Age at the time of surgery ranged from 16 to 47 years. There was a significant downward displacement of soft tissue pogonion. Furthermore, there was a significant mean increase of 2.20mm in inter-alar width and a non-significant mean increase of 1.77mm in inter-alar curvature point width. In conclusion, automatic stereophotogrammetry landmarking analysis of soft tissue effects showed downward displacement of soft tissue pogonion following bimaxillary expansion and transverse widening of the inter-alar width and a tendency towards an increase in inter-alar curvature point width after SARME.