Three dimensional study on change ratios of hard and soft tissue after orthognathic surgery

PURPOSE: To investigate the change ratios of soft and hard tissue after orthognathic surgery three-dimensionally in osseous Class Ⅲ patients, in order to predict postoperative soft tissue three-dimensionally. METHODS: Twenty adult patients were selected as the experimental group, craniofacial spiral CT and three-dimensional (3D) stereophotogrammetry were conducted 2 weeks before surgery and 3 months after surgery. Dolphin imaging software was used to establish 3D image digitizing model and 3D measurement coordinate system. Nineteen soft and hard tissue land marks were selected and matched into 12 pairs. 3D coordinate value of these landmarks were read both before and after surgery and were used for statistical analysis with SPSS 22.0 software package. RESULTS: There was a linear relationship only in Pn/A, Gn'/Gn and Me'/Me in X axis, in Gn'/Gn in Y axis and all pairs of landmarks had a close correlation except UL'/UI and UL/SPr in Z axis. Additionally, the change ratio between soft and hard tissue landmarks of mandible was greater than maxilla. CONCLUSIONS: The changes of soft and hard tissue after orthognathic surgery only lie in Z axis(forward and backward), each pair of matched landmarks exhibits a linear relationship, and the change ratio of mandible is greater than the maxilla.