Using 3D-CT to analyze structural changes in the hyoid bone and upper airway after orthognathic surgery in patients with skeletal Class III anterior open bite

The purpose of this chapter is to report on the use of 3D-CT to investigate structural changes of the hyoid bone and upper airway following orthognathic surgery in skeletal Class III anterior open bite patients, and to make comparisons with patients with normal occlusion. Pre-and post-operative computed tomography (CT) examinations were performed on 12 skeletal Class III anterior openbite patients who were treated with Le Fort I osteotomy and mandibular setback osteotomy. Three-dimensional (3D) images of the total skull, mandible, hyoid bone, and upper airway were evaluated using V-works 4.0TM program. In the Class III openbite group, the hyoid bones were all positioned anteriorly when compared to the normal occlusion group (p<0.05). Before surgery, the angle between the hyoid plane and mandibular plane in the Class III openbite group was greater than that in the normal group (p<0.05), and the differences increased after surgery (p<0.01). In the Class III openbite group, the volume of the upper airway decreased after surgery (p<0.001) and the volume of the upper airway was smaller than the normal group before and after surgery (p<0.001). The narrow upper airway space in the skeletal Class III openbite patients further decreased after Le Fort I osteotomy and mandibular setback osteotomy, which may be a factor in post-surgical stability.