Effects Of Orthognathic Surgery On Upper Airway And Respiratory Function During Sleep In Patients With Skeletal Class Ⅲ Malocclusion

Objectives:1.To investigate the effect of orthognathic surgery on supine upper airway volume and minimum axial area in patients with class III skeletal relationship by spiral CT.2.To study the changes in respiratory function during sleep and whether there is postoperative obstructive sleep apnea（OSA）in patients with skeletal classⅢmalocclusion after orthognathic surgery by polysomnography（PSG）.Methods:1.Twenty-three skeletal class III patients who visited Department of Orthodontics,Hospital of Stomatology,Jilin University from December 2020 to September 2022were selected.All patients underwent Le Fort I osteotomy to advance the maxilla as well as bilateral sagittal split ramus osteotomy（BSSRO）to setback mandibular,and15 of them underwent genioplasty.Spiral CT scans were collected from all patients within one week before surgery,within one month after surgery and six months after surgery.The scans were imported into the Dolphin Imaging software system to form lateral films,the patients’preoperative Wits values as well as ANB angles were measured.And the amount of maxillary advancement,mandibular setback,and chin advancement for genioplasty were measured using Sketchpad 5.06.The changes in nasopharyngeal,oropharyngeal,hypopharyngeal as well as total upper airway volumes and the minimum axial areas of the oropharynx and hypopharynx were also measured preoperatively and six months postoperatively.The statistical analysis tool was SPSS 23.0.2.Twelve patients with skeletal classⅢmalocclusion who visited the Department of Orthodontics,Hospital of Stomatology,Jilin University from June2021 to September 2022 were selected.All patients underwent Le Fort I osteotomy to advance the maxilla as well as BSSRO to setback mandibular,and seven of them underwent genioplasty.Spiral CT scans were collected from all patients within one week before surgery and within one month after surgery.The scans were imported into the Dolphin Imaging software system to form lateral films,the patients’preoperative Wits values as well as ANB angles were measured.And the amount of maxillary advancement,mandibular setback,and chin advancement for genioplasty were measured using Sketchpad 5.06.All patients underwent polysomnography one week before and six months after surgery to obtain apnea hypopnea index（AHI）and lowest Sp O₂to assess changes in respiratory function during sleep before and after surgery.The data were statistically analyzed using SPSS 23.0.Results:1.The mean value of Wits in Study 1 was-11.04±4.42 mm and the mean value of ANB angle was-4.01±2.59°.The mean value of maxillary advancement was 4.55±1.97 mm and the mean value of mandibular setback was 8.64±4.19 mm.The mean value of chin advancement in the fifteen patients who underwent genioplasty was 3.73±2mm.The nasopharyngeal,oropharyngeal,hypopharyngeal as well as total upper airway volumes and the minimum axial areas of the oropharynx did not change significantly before and after surgery（p>0.05）,except for a significant decrease in the minimum axial areas of the hypopharynx（p<0.05）.2.The mean value of Wits in Study 2 was-11.81±5.71mm and the mean value of ANB angle was-4.22±3.09°.The mean value of maxillary advancement was 4.75±1.86 mm and the mean value of mandibular setback was 8.59±3.55mm.The mean value of chin advancement in the seven patients who underwent genioplasty was 2.79±1.45 mm.The AHI and lowest Sp O₂of 12 patients did not change significantly before and after surgery（p>0.05）.No patient was diagnosed with OSA after orthognathic surgery,and two patients who already had mild OSA before surgery became normal after surgery.Conclusions:1.Twenty-three skeletal class III patients’upper airway volumes did not change significantly before and after surgery,except for a significant decrease in the minimum axial areas of the hypopharynx.This may be because the large maxillary advancement and chin advancement both had the effect of promoting an increase in upper airway volume,offsetting the decrease in upper airway volume by the mandibular setback.In contrast,the significant decrease in the minimum axial areas of the hypopharynx may stem from the fact that the larger mandibular setback still had some negative effect on the hypopharyngeal region.2.No patient was diagnosed with OSA after orthognathic surgery in 12 skeletal class III patients,and two patients who already had mild OSA preoperatively became normal after surgery.This shows that the orthognathic surgical design adopted in this study did not increase the risk of patients developing postoperative OSA.