Abstracts Background: The aim of this study was to evaluate area and volumetric changes in the upper airway after maxillary protraction with rapid maxillary expansion (MP/RME) using cone-beam computed tomography (CBCT) in Class III patients, and to relate these to the changes in cephalometric measurements. Methods: Forty skeletal Class III Chinese patients (mean age: 9.6 years; range: 8-12 years) treated with MP/RME were retrospectively recruited. Pretreatment (T1) and post-treatment (T2)

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... dimensional (3D) CBCT scans were used to measure the nasopharyngeal, velopharyngeal, glossopharyngeal, and hypopharyngeal airway changes in terms of volume, sagittal and cross-sectional area. Two-dimensional (2D) linear measurements in the upper airway space, adenoid, tongue, soft palate, and hyoid were performed on the cephalograms derived from 3D scans. Measurements at T1 and T2 were compared with paired t tests. A Spearman correlation analysis was used to evaluate the correlation between T1, T2, and treatment changes from both 3D and 2D measurements. Results: Significant volumetric increases were found in the nasopharynx (P < 0.001), velopharynx (P < 0.01), and total upper airway (P < 0.001). The nasopharyngeal space (PNS-UPW) showed a significant increase (P < 0.001) on cephalograms. The 2D adenoid dimension had a positive correlation with the nasopharynx measurements on CBCT. Conclusion: The volume of the nasopharynx and velopharynx increased significantly after MP/REM treatment. When compared with a 3D normal sample, the results suggest that MP/RME would not inhibit the anticipated increase of upper airway volumes in Class III children in the short-term. Dimensional measurements of the adenoid on cephalometric images are related with the area and volumetric parameters of the nasopharyngeal airway.