Structural And Functional Changes Of Upper Airway In Patients With Skeletal Class Ⅲ Malocclusion After Bimaxillary Surgery

Background and purpose:A three-dimensional upper airway model of skeletal Class III malocclusion was constructed using CBCT data before and after bimaxillary surgery.The anatomical structure of upper airway was analyzed and measured by digital software,and using fluid dynamics software to simulate upper airway ventilation and perform fluid analysis.To explore the anatomic and functional changes of upper airway in patients with skeletal Class III malocclusion one year after bimaxillary surgery,and to provide theoretical basis for clinical orthognathic surgery.Methods:1.Sample screening:A total of 20 patients,10 males and 10 females,aged between 20 and 30 years,who underwent orthodontic-orthognathic surgery in the Stomatological Hospital of Shandong University for at least one year were selected.The patients were examined by CBCT before and one year after operation.2.Build a upper airway model:The CBCT images of the patients before and one year after operation were stored in DICOM format,and then imported into MIMICS to adjust the threshold,remove artifacts and construct the upper airway model.3.Measurement of anatomical morphology of nasal airway:The CBCT images of the patients and the nasal airway model were analyzed and measured by MIMICS software,and the nasal airway anatomical morphology data such as nasal septum deviation,nasal cavity volume,maxillary sinus volume and nasopharyngeal cross-sectional area were measured respectively.4.Measurement of pharyngeal morphology of nasal airway:The CBCT images of the patients and the pharyngeal airway model were analyzed and measured by MIMICS software,and the pharyngeal airway anatomical morphology data such as length,volume,shortest anterior and posterior diameter,minimum cross-sectional area and pharyngeal cross-sectional area of the pharynxnasal were measured respectively.5.Model ventilation simulation:After the model is exported in STL format,the model is optimized by Geomagic and meshed by ICEM.Finally,the model is imported into FLUENT for ventilation simulation,and the results are analyzed.6.Data analysis:SPSS26.0 was used to analyze the data,and the test data were in accordance with normal distribution.Paired t-test was used to compare the anatomical changes of nasal airway before and one year after operation,and single-sample t-test was used to compare the changes of anatomical structure between pre-operation and one year after operation.The hydrodynamic simulation results are analyzed in Tecplot post-processing software.Results:1.The models of nasal airway and pharyngeal airway were successfully reconstructed by digital software.2.The nasal airway morphology of patients with skeletal Class III malocclusion changed significantly after bimaxillary surgery.After bimaxillary surgery,the nasal volume was significantly smaller than that before operation(P<0.05),and the postoperative nasal volume was 13.5%lower than that before operation.The postoperative maxillary sinus volume was significantly smaller than that before operation(P<0.05),and the average maxillary sinus volume was 7.8%lower than that before operation.3.The structure and morphology of pharyngeal airway changed significantly compared with that before surgery.The pharyngeal volume,shortest anterior and posterior diameter and minimum cross-sectional area after surgery were significantly lower than those before operation(P<0.05).The pharynx volume after operation was about 16%lower than that before surgery,and the shortest anterior and posterior diameter of pharynx was about 20%lower than that before surgery.4.After the ventilation experiment on the nasal airway model,the hydrodynamic analysis showed that there was no significant difference in the pressure drop from nostril to nasopharynx(P>0.05),but there was a positive relationship between the pressure drop from nostril to nasopharynx and nasal resistance.Therefore,the results showed that there was no significant difference in nasal resistance before and after operation.There is little difference in the change of nasal resistance.There was no significant difference in the characteristics of airflow in the maxillary sinus after operation,and the results of wall shear stress in nasal airway model were the same before and after operation,that is,no significant change in nasal airway ventilation function was found after orthodontic surgery.5.Based on the hydrodynamic simulation analysis of the pharyngeal airway model,it was found that the postoperative pharyngeal airway resistance was higher than that before operation.There was a correlation between the minimum cross-sectional area and the maximum pressure,and the minimum cross-sectional area was inversely proportional to the maximum pressure.Conclusion:In patients with skeletal Class Ⅲ malocclusion,after bimaxillary surgery,the anatomical morphology of nasal airway and pharyngeal airway changed compared with that before operation.The nasal airway ventilation function did not change significantly,but the pharyngeal airway resistance increased.Standard bimaxillary surgery has little effect on nasal airway function in patients with skeletal class Ⅲmalocclusion,but the increase of postoperative pharyngeal airway resistance should be considered when designing the amount of mandibular recession before operation.