Purpose: Orthognathic surgery to improve skeletal open bite may change the function of peripharyngeal muscles, pharyngeal airway and hyoid bone position. The purpose of this study was to investigate cephalometric changes in hyoid bone position and pharyngeal airway morphology following mandibular setback surgery in patients with skeletal open bite.
Material and Methods: The subjects were 13 patients (4 males and 9 females, mean age: 27 years 11 months) who had undergone sagittal split ramus osteotomy to improve skeletal open bite. The mean displacement of the mandible was 2.1mm posteriorly and 5.0mm superiorly after surgical intervention. Lateral cephalograms taken at pre-surgery (T1), post-surgery (T2) and 1 year after surgery (T3) were used to examine pharyngeal airway morphology and the position of the hyoid bone. The lowermost anterior edge of the third cervical vertebra (C3), the upper protruding part of the hyoid bone (H1) and the lower protruding part of the hyoid bone (H2) were defined as reference points to evaluate hyoid bone position. Anteroposterior airway width (APW-PPW) was evaluated with reference to APW1-PPW1 at the nasal pharynx, APW2-PPW2 near the soft palate, APW3-PPW3 near the uvula, APW4-PPW4 near the mandibular angle, and APW5-PPW5 near the epiglottis.
Results: ∠NSH1, ∠NSH2 and ∠H1C3H2 significantly increased in the time periods of T1-T2 and T1-T3. No significant difference was seen in C3-H1, while C3-H2 significantly decreased in the time periods of T1-T2 and T1-T3. Morphological evaluation of the pharyngeal airway did not reveal a significant difference in the upper and lower parts of the pharyngeal airway, which correspond to APW1-PPW1, APW4-PPW4 and APW5-PPW5. Stenosis was found in APW2-PPW2 and APW3-PPW3, which correspond to the middle part in the time periods of T1-T2 and T1-T3. No significant changes were seen from T2 to T3.
Conclusions: These results revealed that the hyoid bone had rotated clockwise and was displaced posteroinferiorly. Furthermore, superior displacement of the mandible causes airway stenosis at the middle part.
