Abstract
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.