A 2-year follow-up of changes after bimaxillary surgery in patients with mandibular prognathism: 3-dimensional analysis of pharyngeal airway volume and hyoid bone position.

Purpose: The aims of this study were to use 3-dimensional cone-beam computed tomography (CBCT) to evaluate how the upper airway and hyoid bone position changed after orthognathic surgery in patients with skeletal Class III malocclusions and to analyze the relations among upper airway changes, the change in the position of the hyoid bone, and postsurgical stability.

Materials And Methods: CBCT scans were obtained from 15 patients with mandibular prognathism before surgery (T0), 6 months after surgery (T1), 1 year after surgery (T2), and 2 years after surgery (T3). Positional displacement of the hyoid bone was assessed using the coordinates at T0, T1, T2, and T3. In addition, the volume of each patient's pharyngeal airway was measured. Differences in CBCT scans at the established time points were determined by the Wilcoxon signed rank test. The Spearman correlation coefficient was used to determine the relations among changes in hyoid bone position, airway volume, and skeletal reference points.

Results: The hyoid bone moved backward at 6 months after surgery (T0 to T1), and the total volume of the pharyngeal airway was considerably decreased at the same time points. At 1 year after surgery (T1 to T2), although the hyoid moved more posteriorly and the total volume of the pharyngeal airway was decreased, the changes were not major. At 2 years after surgery, the hyoid bone moved anteriorly and the size of the upper pharyngeal airway was increased (T2 to T3).

Conclusion: The hyoid bone moved posteriorly and the pharyngeal airway volume was decreased at 6 months after bimaxillary surgery. These measurements had a tendency to recover at 2 years postoperatively. The decrease in pharyngeal airway volume was not correlated with positional changes of the hyoid bone.