The positional relationship between the mandible and the hyoid bone in mandibular protrusion after orthognathic surgery evaluated with 3-d ct

ABSTRACT

PURPOSE: This study was intended to evaluate the positional relationship between the hyoid bone and the mandible in patients with mandibular protrusion after mandibular set-back surgery by means of 3D-CT. MATERIALS AND METHODS: Preoperative(3 weeks before) and postoperative (6 weeks after) 3D-CT and cephalogram were taken on 32 patients(12 male, 20 female, mean age of 23.2) treated by bilateral sagittal split osteotomy with rigid fixation. The angular measurement on 3D-CT basilar view were deviation of Me and H, long axis angle of left and right cornu majus. The lineal measurement on 3D-CT basilar view were composed of intercondylar line and coordinates(x,y) of Me and H. The angular and lineal measurement of lateral cephalogram were composed of mandibular plane angle, SNA, SNB, ANB, FH-NA and FH-NB, and coordinates(x,y) of B, Pog, Me and H, PAS, Lpw, MPH and IAS. On the frontal cephalogram, deviation of Me were evaluated. RESULTS: The mean mandibular set-back was 8.0mm horizontally and mandibular plane angle was slightly increased. The hyoid bone was displaced postero-inferiorly, the distance between MP(mandibular plane) and H(hyoid bone) was increased and the posterior airway space values (PAS, Lpw, IAS) were decreased. The coordinates Me(x,y), H(x,y) and deviation angle Me' and H'were revealed the strong positive correlation. CONCLUSION: The results revealed that the horizontal, vertical and transverse relationship of the mandibular and the hyoid bone movements were significantly correlated in patients performed mandibular set-back surgery.