The Effect of Orthognathic Surgery on the Hyoid Bone Position in Skeletal Class III Patients: An Evaluation Using Cephalometric Analysis.

Background: This study aimed to investigate the positional changes of the hyoid bone following orthognathic surgery in skeletal class III patients.

Methods: This double-blinded quasi-experimental study was carried out in Mashhad University of Medical Sciences, Iran, from Apr 2019 to Jun 2020. All skeletal Class III patients who were candidates for orthogenetic surgery were included. They underwent mandibular setback surgery using bilateral sagittal split osteotomy. Cephalometric assessments in relation to hyoid bone position and posterior airway space (PAS) were conducted one day preoperatively (T0), as well as one week (T1), six months (T2) and one year (T3) postoperatively, determining the parameters like the Long axis of the hyoid bone (LAH), Retrognation (RGn), Hyoidale (H), Palatal plane (PP), Mandibular plane (MP) and C3 Vertebrae (C3). All cephalograms were examined using AudaxCeph, Planmeca software. The data analysis was performed via SPSS-19 (<0.05).

Results: 25 class III patients, including 18 females (72%) and 7 males (28%) with a mean age of 24.32±5.87, were studied. The cephalometric analysis demonstrated significant decreases in variable angles during the follow-up periods, except for LAH-MP angle (<0.001). The hyoid bone moved downward and backward relative to its original position following the mandibular setback surgery. However, the bone gradually returned to the preoperative location between 6 to 12 months postoperatively.

Conclusion: The findings revealed the downward and backward movement of the hyoid bone following the mandibular setback surgery, returned near to its preoperative position after 1 year, postoperatively.