Three dimensional evaluation of airway changes post orthognathic surgery in patients with Class III deformity

Objective: The aim of the present study is to assess the effects of surgical movements on the pharyngeal airway space (PAS), minimum cross-sectional area (MCA) and their relationship with various reference points, angles, or planes used in deformity analysis. Materials and Methods: Forty-nine patients with skeletal Class III deformities (30 females, 19 males) who underwent bimaxillary orthognathic surgery were included in this retrospective study. Computed tomography (CT) scans obtained prior to surgery for three-dimensional virtual planning and during a follow-up period of at least 6 months were utilized. Reconstructions of these scans and lateral cephalometric graphs were obtained using NemoStudio (NemoFab, v2020) software. Ten linear and two angular measurements (FMA and maxillary occlusal plane) were made using various cephalometric landmarks (A, B, PNS, Me), with the Frankfurt horizontal plane and a perpendicular vertical reference line defined on the lateral cephalometric images to evaluate surgical movements of maxilla and mandible. To analyze total and diagonal displacement of the hyoid bone and its relationship with the mandible, the distance between the body of the hyoid bone and the third cervical vertebra (HC3), and the shortest distance between the hyoid bone and the lowest border of the mandible (HBM) were measured. Additionally, volumetric measurements of the nasopharyngeal (NP), oropharyngeal (OP), and total pharyngeal (TP) airways and MCA on the oropharynx were completed based on the three-dimensional model of the airway obtained through the same software. Pre- and post-operative changes were statistically analyzed with Wilcoxon signed-rank test, Pearson and Spearman's rank correlation coefficient for correlation analysis. Results: Significant reductions were observed in total airway volume (p < 0.04) and oropharyngeal airway volume (p < 0.028) postoperatively, while nasal airway volume showed a non-significant decrease (p < 0.056). There was no significant change in the minimum axial section area postoperatively (p < 0.724). Correlation analysis revealed significant associations between changes in airway volume and cephalometric landmarks, including vertical and horizontal reference planes and hyoid bone position (p < 0.05). Oropharyngeal airway volume showed a positive correlation with total airway volume (p < 0.001) and minimum axial section area (p < 0.001). Additionally, nasal airway volume correlated significantly with maxillary occlusal plane angle (p < 0.001). Conclusion: Bimaxillary orthognathic surgery, including mandibular setback surgery, resulted in significant reductions in total and oropharyngeal airway volumes, with no significant change in the minimum axial section area. Changes in airway volume were correlated with cephalometric landmarks, indicating the importance of considering airway changes in orthognathic surgery planning and evaluation. Keywords: Pharyngeal airway volume, orthognathic surgery, minimum cross-sectional area