Three-dimensional evaluation of pharyngeal airway changes after bimaxillary orthognathic surgery in Class III malocclusion

Abstract

The aim of this study was to evaluate the pharyngeal airway changes in Class III patients after bimaxillary surgery with intraoral vertical ramus osteotomy (IVRO) using three-dimensional computed tomography (3-D CT). Experimental group consisted of 52 Class III patients (27 males, 25 females; mean age, 21.6±4.8 years) who underwent bimaxillary surgery with mandibular setback via IVRO. All patients were divided into two groups according to maxillary movement pattern at PNS point; Group I as maxillary advancement group and Group II as maxillary setback group. 3-D CT images were taken at pre-surgery (T0), after surgery (T1) and 1 year after surgery (T2). The results were as follows:1.After surgery (T0-T1), the nasopharynx volume, oropharynx-high volume and total pharynx volume significantly decreased in Group I (p < 0.01) and Group II (p < 0.01). 2.After 1 year follow-up (T1-T2), there was no significant change in the pharyngeal volume except for hypopharyngeal volume decrease in Group I (p < 0.05). 3.After surgery (T0-T1), cross sectional area (CSA) significantly decreased at PNS plane and CV1 plane in both two groups (p < 0.001). The CSA increased at CV3 (p < 0.01) and CV4 (p < 0.05) plane in Group II. After 1 year follow-up, CSA at PNS level recovered to pre-surgical measurements leaving CSA at CV1 level statistically significant (p < 0.001) (T0-T2).4.Comparing before surgery and 1 year after surgery (T0-T2), the antero-posterior (AP) length significantly decreased at CV1 level in Group I (p < 0.001). In Group II, AP length decreased at CV1 level (p < 0.001) and increased at CV4 level (p < 0.01).5.Comparing before surgery and 1 year after surgery (T0-T2), the transverse width (TW) significantly decreased at CV1 (p < 0.001), CV3 (p < 0.05), CV4 (p < 0.01) level in Group I. In Group II, TW decreased at CV1 level (p < 0.001). The results indicate that bimaxillary surgery with mandibular setback in Class III patients lead to decrease in pharyngeal airway volume and there was no significant recovery for 1 year follow-up period except for decrease in hypopharynx volume. The changes of upper airway volume correlated to measurement of mandibular reference point (B point), thereby being useful to prevent the risk of pharyngeal airway volume decrease obstructive sleep apnea(OSA) caused by surgery.