Changes In Nasopharynx,Oropharynx,and Soft And Hard Tissue Around Pharyngeal Airway After Bimaxillary Surgery For Patients With Skeletal Class Ⅲ Malocclusion

Skeletal Class Ⅲ malocclusion is a common dento-maxillofacialdeformity. It not only affects patients’ profile but affects their masticatoryfunction and mental health. For patients suffering from severe skeletal ClassIII malocclusion, a simple orthodontic treatment cannot achieve satisfactoryresults. Thus, the combination of orthognathic surgery and orthodonticstreatment is widely used to improve occlusion, masticatory function, andesthetics by markedly changing the position of the jaws. The positions of thehyoid bone and the tongue are also changed, with consequent narrowing of thepharyngeal airway space (PAS) that might be a factor in obstructive sleepapnea. However, most of previous investigations about the effects ofbimaxillary surgery on the pharyngeal airway in patients with skeletal ClassIII malocclusion were based on lateral cephalometric analysis, which only provide2-dimensional images of complex3-dimensional anatomic structure.The method of observation and measurement for the pharyngeal airway islimited. The effects of bimaxillary surgery on the upper airway for correctingskeletal Class III malocclusion have not been sufficiently explored, and,therefore, a study based on a3-dimensional evaluation to investigate thechanges in nasopharynx， oropharynx， and soft and hard tissue aroundpharyngeal airway after bimaxillary surgery is needed.In this study we used CBCT to observe the changes of pharyngeal airwayin three dimensional which can provide reference to the treatment plan ofskeletal Class Ⅲ malocclusion in clinical.Objective：CBCT was taken before and after surgery, mimics was used to builtnasopharynx，oropharynx3-dimensional images, and to calculate the changesof volume of the nasopharynx，oropharynx，The position of the hyoid bone,the morphology of the soft palate, and head posture. To provide reference tothe treatment plan of skeletal Class Ⅲ malocclusion in clinical.Methods1．To consult with maxillofacial department,19patients (12women，7men，average age：23.8) who need bimaxillary surgery were involved in this study．2．The3D CBCT images of nasopharynx and oropharynx for volumetricanalysis were built by Mimics10.01．3．T-test was performed for the comparisons of the differences between pre-and post-operative variables and the association between the pre-andpost-operative was evaluates with Pearson’s correlation coefficient. Statisticaltests were performed using SPSS19.0.Result 1．The changes of the pharyngeal airwayThe volume of oropharynx and the axial section area of the soft palatewere significant changed (P<0.05).The total volume of nasopharynx andoropharynx changed significant from pre-operative28.51±9.38mm3topost-operative26.54±9.05mm3.But the changes of the nasopharynx and thearea of lower boundary of it was not significant (P>0.05).2．The changes of hyoid boneThe anterior and posterior of the hyoid bone both had significantlyreduced in the horizontal. The posterior of the hyoid bone had great increaseafter surgery. It indicate that the hyoid had posterior and inferior movementafter surgery.3．The changes of the morphology of the soft palate and the head posture.The length of the soft palate (PNS-UT) increased from29.11mm to30.38mm, had significant increase. The thickness of the soft palate (U-T) hadsignificant decreas（eP<0.05）.But the angle of the soft palate UT/ANS and thehead posture (CVT/OPT,OPT/NSL,CVT/NSL) had no changes after surgery.4．The correlationsThe position changes of the hyoid bone (H-X,H-Y,GH-Y) had significantcorrelation with the change of oropharynx. A similar relationship was revealedbetween the morphological changes of the soft palate and the oropharynx. Thechange of cervical curvature (CVT/OPT) also showed great correlation withthe volume decrease of oropharynx (r=-0.596，P=0.007). The changes ofsurrounding soft and hard tissue of the pharyngeal airway after surgeryrevealed great connections between each other. The horizontal movement ofhyoid bone (H-X) was related to the change of the length of the soft palate(PNS-UT)(r=-0.796), where the correlations between the vertical change of the hyoid bone (H-Y) and the change of the thickness of the soft palate (U-T)(r=-0.803).ConclusionBimaxillary surgery could not prevent the narrowing of the pharyngealairway space in the correction of Class Ⅲ malocclusion, the volumes of thepharyngeal airway space still decreased after surgery．The potential impact oforthognathic surgery on the pharyngeal airway space should be considered inthe treatment plan．...