Abstract: Objective：To evaluate the changes of different parts of upper airway after alternating rapid palatal expansion and constriction via three dimensional measurement, compared with the protocol of ra-pid palatal expansion alone. Methods: In the study, 36 patients with retrognathic maxilla were selected and randomized to either group A or group B. The patients in group A were treated with rapid palatal expansion alone. The patients in group B were treated with alternating rapid palatal expansion and constriction. Three dimensional analyses were performed on all pre-and post-treatment cone-beam computed tomography (CBCT) images with the software Dolphin. Results: Two subjects in group B were lost to follow up during the treatment. The gender distributions, ages and all measuring items before treatment had no significant difference between group A and group B (P＞0.05). Nasal floor width, nasal lateral width, nasal volume, and nasopharynx volume increased significantly in each group after rapid palatal expansion alone or rapid palatal expansion and constriction (P＜0.05). The variations of oropharyngeal volume and hypopharyngeal volume had no significant difference (P＞0.05). No significant difference was observed in the nasal floor width and nasal lateral width increment among the anterior, median and posterior parts in each group either (P＞0.05). No significant difference in all the measuring items was observed between the two groups (P＞0.05). Conclusion:Alternating rapid palatal expansion and constriction could increase the volume of nasal and naopharynx cavities by the similar way of rapid palatal expansion alone, and had no obvious effect on oropharynx and hypopharynx cavities.

Key words: Palatal expansion technique, Cone-beam computed tomography, Upper airway