CBCT Evaluation Of The Upper Airway Morphological Changes In Growing Patients Of Skeletal Class Ⅲ Malocclusion Using Protraction And Rapid Maxillary Expansion Appliance

Objective:Class Ⅲ malocclusion is characterized by a deficiency of the maxilla, or prognathism of the mandible, or the maxilla and mandible dysplasia. The patients with this type of malocclusion commonly present with a concave profile, an anterior crossbite relationship, and a Class Ⅲ molar relationship. Maxillary or mandibular abnormalities could affect the morphology of the upper airway. The protraction headgear and rapid maxillary expansion (PE) treatment leads to the forward displacement and the growth of the maxilla, meanwhile it limits the growth of mandible and promotes mandibular clockwise rotation. This aim of this study was to evaluate the morphological changes of upper airway after PE treatment in growing patients with Class Ⅲ malocclusion and maxillary skeletal deficiency compared with untreated Class Ⅲ patients by Cone-beam computed tomography (CBCT).Materials and Methods:The 60 patients (28 girls and 32 boys) were selected from the Department of Stomatology, Qilu Hospital of Shandong University and Department of Orthodontics, School of Dentistry, Shandong University during 2011-2014 years. All patients were in the growth period with Class III malocclusion and maxillary skeletal deficiency. The PE group includes 30 growing patients who have completed PE treatment. The control group (n=30) was selected from the growing untreated patients with the same diagnosis. The CBCT scans of the pre-treatment (T1) and post-treatment (T2) of PE group and the control group were collected. Reconstruction and registration of the 3D models of T1 and T2 were completed. Then the changes of the upper airway were measured. By comparing the data obtained from T1, T2 and control group, the morphological changes of the upper airway during the PE treatment were evaluated. The paired t-test was used for comparisons between T1 and T2 data. The independent t-test was used for comparisons between T2 and control data.Results:In the PE group, the subspinale (A) was advanced by 2.88±0.88 mm in the horizontal direction and 1.23±1.32 mm in the vertical direction. The Upper incisor (UI) was moved anterosuperiorly by 3.28±1.05 mm and 1.49±1.06 mm in horizontal and vertical direction, respectively. The gnathion (Gn) was moved postero-inferiorly by 3.40±0.93 mm and 3.66±1.06 mm in horizontal and vertical direction, respectively. The displacement of the hyoid bone in horizontal and vertical direction had a significant difference. After the PE treatment, the dental arch length and width had significant difference. The upper airway showed a significant difference in the volume and mean cross-sectional area at the nasopharynx, velopharynx and glossopharynx regions, but the hypopharynx showed no significant difference. The AP/LR ratio of the velopharynx and glossopharynx was increased, but the AP/LR ratio of the hypopharynx was decreased. As for the comparison of the control group and T2 group, the length and width of the maxillary dental arch, the displacement of the hyoid showed significant difference. There were significant difference in the volume and mean cross-sectional area at nasopharynx and velopharynx after the treatment, but no significant changes in the glossopharynx and hypopharynx were found following treatment. The AP/LR ratio of the velopharynx was increased significantly, but the AP/LR ratio of the hypopharynx was decreased. The AP/LR ratio of the nasopharynx and glossopharynx had no significant changes.Conclusion:The nasopharynx and velopharynx of growing patients with Class III malocclusion and maxillary skeletal deficiency showed a significant enlargement after the PE treatment. The glossopharynx and hypopharynx have no significant difference in a short-term. In addition, the velopharynx became more circular and the hypopharynx became more elliptic in transverse shape after PE treatment.