Assessment of Changes in the Hyoid Bone Position Following Orthognathic Surgery in Class III Patients

Background: The hyoid bone position may change in class III patients following different surgical procedures, including mandibular setback, maxillary advancement, and bimaxillary advancement. Objectives: The aim of this study was to conduct a detailed cephalometric evaluation of changes in the hyoid bone position following treatment of class III skeletal deformities via different surgical procedures (ie, mandibular setback, maxillary advancement, and bimaxillary advancement). Methods: A total of 120 consecutive patients, who were diagnosed with skeletal class III deformities, were recruited in this study. All the patients were adults with complete growth and cephalograms taken at 1month before operation (T1) and 1 to 9months postoperation (T2) in the natural head position. The patients were divided into 3 groups according to the type of surgery: group 1, bimaxillary advancement; group 2, mandibular setback; and group 3, maxillary advancement. The hyoid bone position was evaluated at both T1 and T2 in each group. The results were compared using paired t test and one-way ANOVA. Results: The hyoid bone position showed no significant changes in groups 1 and 3 (P < 0.05), whereas a significant difference was found both horizontally and vertically in group 2 (P < 0.05). Conclusions: The hyoid bone position changed only after mandibular setback surgery; the bone was displaced downward and backward following mandibular retraction. On the other hand, neither bimaxillary nor maxillary advancement could change the hyoid bone position.