Evaluation of the effects of two different modes of orthognathic surgery on upper airway morphology in patients with skeletal Class III malocclusion

PURPOSE: To establish three-dimensional models of upper airway pre- and post-orthognathic surgery in patients with skeletal Class Ⅲ malocclusion, and to compare the effects of different modes of orthognathic surgery on the cross-sectional areas and volumes of upper airway. METHODS: Twenty-eight patients with skeletal Class Ⅲ malocclusion were divided into 2 groups. Group A (12 patients) underwent bilateral sagittal split ramus osteotomy(BSSRO) for mandibular setback, named single jaw surgery group; group B (16 patients) underwent BSSRO + Le Fort I osteotomy for mandibular setback and maxillary advancement, named bimaxillary surgery group. All patients received CT scanning before (T1) and 3 months after surgery (T2). The three-dimensional models of the upper airway containing velopharynx, glossopharynx and laryngopharynx were established by using Dolphin Imaging 11.7 software. The changes of sagittal diameters, coronal diameters, cross-sectional areas and volumes of the upper airway were measured and compared between the two groups pre- and post- surgery (T1, T2) using SPSS 16.0 software package, respectively. RESULTS: In velopharynx, the values of group A were decreased after surgery, while the other values of group B were increased except the value of coronal diameter. There was a significant difference between the two groups (P<0.05). In glossopharynx and laryngopharynx, the values of group A and group B were both decreased after surgery. The reduction of the cross-sectional areas and volumes in group A were more obvious than group B (P<0.05). CONCLUSIONS: The amount of narrowing of the upper airway is smaller in patients undergoing bimaxillary surgery than in patients undergoing mandibular setback surgery.