The Long-Term Changes of Skeletal-Facial Patterns and Airway Volumes Using Surgery-First Approach of Orthognathic Surgery to Correct Mandibular Prognathism---A Prospective Cohort Study

The surgery-first approach is becoming a new trend for orthognathic surgery. At present, more than 70% of orthognathic surgery is in Skeletal Class III correction. Skeletal Class III cases are often associated with maxillary deficiency, upper dental crowding and labially proclined upper incisors, in addition to mandibular prognathism. Clockwise (CW) rotation of maxillomandibular complex (MMC) could accentuate midface fullness and correct the axis of proclined incisors and provide more mandibular setback. Bimaxillary surgery using CW rotation of MMC has become the major surgical procedure for mandibular prognathism. However, more evidences are needed to support the use CW rotation of MMC in surgery-first approach, especially for the long-term skeletal dental stability, airway volume changes and soft-tissue facial appearance. A prospective cohort study on will be designed to investigate the following questions on those patients receiving bimaxillary surgery with CW rotation to correct mandibular prognathism. 1. Does CW rotation of MMC affect the skeletal long-term stability? 2. Does CW rotation of MMC affect the long-term nasopharyngeal airway? 3. Does CW rotation of MMC affect the long-term facial appearance? Enrollment of 120 patients with mandibular prognathism will be included in the present study. Orthodontic records including intraoral and extraoral photographs, three dimensional face scan by 3dMd, lateral and posterioanterior cephalograms, panoramic radiograph, and cone-beam computed tomography will be taken before surgery (T1), immediately after surgery (T2; within 1 month of surgery), and one year after surgery (T3, approximate at time of orthodontic debonding). For each time point, 3D image analysis includes three parts: (1) CBCT skeletal dental analysis, (2) CBCT airway volume, (3) 3dMD facial scan. Serial CBCT images to evaluate skeletal dental changes after the surgery include 4 steps: (1) surface model construction, (2) image registration, (3) transparency overlay, and (4) quantitative measurement. The quantitative changes are visualized by the use of color maps. Eighteen regions of interest are selected and the largest displacement of each region is calculated for T1 to T2, T1 to T3, and T2 to T3. For airway volume analysis, upper airway volume will be divided into oropharynx (OP) and nasal passage (NP). NP and OP will be compared at T1, T2 and T3. The relation of NP and OP to the degrees of CW rotation of MMC will be elucidated. For soft tissue analysis, focus will be placed on three major esthetic units including nose, lip and para-nasal area at T1, T2, and T3. The major outcomes from this study could be anticipated as the follows. 1. A new 3D superimposition method using entire cranial base as a reference will be developed to be a reliable reference to describe overall facial changes relative to the cranial base, maxilla, mandible, per se. 2. The 3D changes of skeletal dental changes, airway volume changes, and facial appearance after CW rotation of MMC at T1, T2, and T3. 3. To correlate CW rotation of MMC with skeletal dental stability, airway volume changes and facial appearance.

Project ID:PC10401-0621
External Project ID:MOST103-2314-B182-042-MY2