Effective three‐dimensional evaluation analysis of upper airway form during oral appliance therapy in patients with obstructive sleep apnoea

The oral appliance (OA) is considered to be an effective treatment modality for obstructive sleep apnoea (OSA). Upper airway enlargement during OA therapy is critical, and lateral cephalometry has been used for the two‐dimensional evaluation of upper airway form during this therapy. However, this method cannot provide an accurate three‐dimensional (3D) view of upper airway form. To confirm the effects of OA on the upper airway in patients with OSAS, we performed CT in the presence and absence of OA in 15 Japanese patients (12 males, 3 females) who responded to OA therapy. CT in the presence and absence of OA was consecutively performed for each patient, and upper airway cross‐sectional area in six arbitrary planes parallel to the palatal plane was measured. Next, 3D image reconstruction was performed; morphological changes in upper airway form were evaluated, and upper airway volume at three levels from the palatal plane to the deepest point of the epiglottis was measured. The cross‐sectional area of two planes in the posterior soft palate region significantly increased in the presence of OA compared with that in the absence of OA. In the presence of OA, upper airway cross‐sectional area and volume significantly increased in the posterior soft palate region compared with those in the posterior tongue region. 3D CT image reconstruction accurately confirmed morphological changes in the upper airway during OA therapy. Continued use of this 3D evaluation is expected to improve the results of OA therapy in the future.