IMPORTANCE Mandibular contour surgeries (MCS) involving reduction gonioplasty and genioplasty are rewarding for patients with square faces; however, the procedure has inherently difficult clinician learning curves and unpredictable skill acquisitions. To our knowledge, there has been no effective, validated training model that might improve training and surgical outcomes for MCS. OBJECTIVE To establish and evaluate a standardized intraoral MCS training system. DESIGN, SETTING, AND PARTICIPANTS Intraoral MCS training models were constructed by 3-dimensional (3D) skull models covered with elastic head cloths. From April 2016 to April 2018, 90 consecutive MCS patients (30 per group) and 15 craniofacial surgery fellow physicians (5 per group) were enrolled in the prospective observational study. They were randomly divided into intervention groups (A and B) and a control group (C). Intervention groups A and B completed 5 training sessions on the intraoral MCS training models before each clinical case. Group A performed both the model training sessions and clinical surgeries with surgical templates. Control group C had no extra training before clinical surgeries. All groups completed clinical surgery under supervision on 6 patients. The duration of follow-up was at least 3 months postoperatively. INTERVENTIONS Intraoral MCS training models were provided to intervention groups (A and B) before clinical surgeries. Surgical templates were provided to intervention group A both in training sessions and clinical surgeries. MAIN OUTCOMES AND MEASURESThe completion time, surgical accuracy, learning curves, operating confidence, surgical skill, and outcome satisfaction of each procedure were recorded and analyzed with paired t test and 1-way analysis of variance test by blinded observers.RESULTS All 90 patients (14 men, 76 women; mean [SD] age, 26 [5] years) were satisfied with their postoperative mandible contours. The intervention groups (A and B), especially the group with surgical templates (A) showed improvements in clinical surgery time (mean [SD], group A 147.2 [24.71] min; group B, 184.47 [16.28] min; group C, 219.3 [35.3] min; P = .001), surgical accuracy (mean [SD], group A, 0.68 [0.22] mm; group B, 1.22 [0.38] mm; group C, 1.88 [0.54] mm; P < .001), learning curves, and operators' confidence and surgical skill. CONCLUSIONS AND RELEVANCEThe intraoral MCS training model was effective and practical. The optimal intraoral MCS training system included intraoral MCS training models and surgical templates. The system significantly decreased clinical surgery time, improved surgical accuracy, shortened the learning curve, boosted operators' confidence, and was associated with better acquisition of surgical skills.LEVEL OF EVIDENCE NA.

Quantitative information on the normal size range of the masticatory muscles needed for successful treatment of facial asymmetry is sparse. Our purpose in this study was to define morphological indicators for the volume of the masticatory muscles on CT. Cross-sectional areas and volumes of the masseter and medial pterygoid muscles were measured from CT scans of 65 patients. The muscles were scanned from origin to insertion and the maximum cross-sectional area (MCSA) and its location together with the total volume were determined. The mandibular foramen was used as a landmark to determine the location of MCSA. The location of MCSA of masseter muscle was centred 8 mm above the mandibular foramen, and that of medial pterygoid muscle at the foramen. The MCSA of both muscles was highly correlated with volume suggesting that this parameter might serve as an indicator of their volume. Knowledge of the location of the MCSA would facilitate its measurement and so reduce radiation exposure. There was a positive correlation between the two muscles for both volume and MCSA. This finding could be relevant for future studies of the relationship between the morphology, biomechanics and pathology of the masticatory muscles.

After reduction gonioplasty, the masseter muscle atrophied (reduced 20.98% ± 8.75%), especially the lower part of the masseter muscle in the long-term follow-up. Most patients with prominent mandibular angles should be treated with reduction gonioplasty without approaching the masseter muscle.