Changes Of Airway Before And After Orthodontic Treatment In Patients With Mandibular Retrusion Or Bimaxillary

Class Ⅱ Division 1 malocclusion is always seen in clinical,which always showed mandibular retraction and maxillary protrusion.Using functional appliance to move mandibular forward can correct the problem of mandibular retraction in sagittal,thus improving the upper airway volume.Considering that the narrowest part of the airway is usually located at the tip of the soft palate or the root of the tongue,the change of the tongue position(the tip of the tongue is located at the incisor papilla,the back of the tongue is attached to the upper palate and the lingual surface of posterior teeth)has a great influence on the airway volume and the minimum cross-sectional area of the airway.To determine the effect of different tongue positions on the upper airway volume in Class Ⅱ patients with mandibular retraction after moving mandibular forward,we choose 33 cases with class Ⅱ Division 1 malocclusion and mandibular retrusion.They were divided into 2 groups,the control group(12 patients)and test group(21 patients).In the test group,according to the tongue position showed by CBCT,the patients were divided into lower tongue position group and higher tongue position group.The test group was treated with Twin-block appliance,and CBCT was taken before treatment and after 8 months.The control group was taken CBCT in the first months and eighth months.The changes of oropharyngeal airway volume and the minimal cross-sectional area were performed by using Dolphin software.The result showed that after 8 months,the airway volume and the minimal cross sectional area of the oropharynx in the control group were not significantly changed,but increased in the experimental group,especially in the higher tongue position group.To further clarify the effect of different tongue positions on upper airway volume,we studied the changes upper airway before and after treatment of bimaxillary protrusion deformity.Bimaxillary protrusion deformity is also a common dentofacial deformity in clinic.The facial features of bimaxillary protrusion deformity include anterior labial inclination,incomplete closure of labial muscles and protrusion of the middle face.For patients with mild or moderate bimaxillary protrusion,orthodontic treatment usually chooses to extract four first premolars and then retract the upper and lower anterior teeth with strong anchorage.There is still controversy about whether tooth extraction can lead to airway narrow,however,orthodontists should be cautious in making treatment plans because smaller upper airways may lead to snoring or even obstructive sleep apnea(OSA).To determine whether the airway narrow will happen after tooth extraction and the effect of tongue muscle training on airway,we choosed 14 class I malocclusion cases with bimaxillary protrusion.The patients were asked to do tongue exercise.All patients were treated by extraction of four first premolars followed by retraction of anterior teeth with maximum anchorage.Before and after treatment,the CBCT was taken.The changes of upper and lower anterior teeth,maxilla,and mandible in sagittal were performed in lateral cephalogram.The changes of oropharynx,glossopharynx and velopharynx airway volume and the minimal cross-sectional area of oropharynx,were performed by Dolphin software.The result showed that the upper and lower anterior teeth were significantly moved backward in sagittal,but the maxilla and mandible did not changed compared with beginning.After treatment,the airway volume of the oropharynx and glossopharynx were not significantly changed;the velopharynx airway volume was significantly increased;the cross sectional area of oropharynx was not significantly changed;in the lower tongue position group,the tongue raised to normal position after tongue exercise,and the volume of oropharynx and glossopharynx increased,and the minimum cross-sectional area of oropharynx increased;in the higher tongue position group,there is no change after treatment.