Genioplasty is performed for the orthognathic surgical correction of dentofacial deformities. This article reports a safe and accurate method for genioplasty combining a novel three-dimensional (3D) device with mixed reality (MR)-assisted surgery using a registration marker and a head-mounted display. Four types of devices were designed based on the virtual operation: a surgical splint with a connector; an osteotomy device; a repositioning device; and a registration marker. Microsoft HoloLens 2 and Holoeyes MD were used to project holograms created using computed tomography (CT) data onto the surgical field to improve the accuracy of the computer-aided designed and manufactured (CAD/CAM) surgical guides. After making an incision on the oral vestibule, the splint was fitted on the teeth and the osteotomy device was mounted at the junction site, placed directly on the exposed mandible bone surface. Temporary screws were fixed into the screw hole. An ultrasonic cutting instrument was used for the osteotomy. After separating the bone, a repositioning device was connected to the splint junction and bone segment, and repositioning was performed. At the time of repositioning, the registration marker was connected to the splint junction, and mandible repositioning was confirmed three-dimensionally through HoloLens 2 into the position specified in the virtual surgery. The rate of overlay error between the preoperative virtual operation and one-month postoperative CT data within 2 mm was 100%. CAD/CAM combined with MR enabled accurate genioplasty.

The treatment of dentofacial deformities generally includes orthognathic surgery in which mandibular condyle changes following surgery are a common cause of relapse. This study investigated the changes in the mandibular condyle and related muscles to identify the factors that affected the changes in the mandibular condyle after orthognathic surgery in skeletal class II patients. This research studied 60 joints in 30 patients with skeletal class II dentofacial deformities who received surgical orthodontic treatment, including bilateral sagittal split ramus osteotomy, and underwent computed tomography before and after orthodontic treatment. The mandibular condyle, masseter, and medial pterygoid muscles were reconstructed and measured in 3D. Condylar positional and morphology changes, masseter and medial pterygoid muscle volume, temporomandibular joint (TMJ) pain, and distal segment movement were analyzed. The study observed that both the masseter and medial pterygoid muscle volumes decreased with statistical significance. The changes in the horizontal direction were positively correlated with the amount of movement. The findings indicated that mandibular condyle changes were significantly affected by the movement of the distal segment, the medial pterygoid muscle volume, and the direction of the distal segment, which influenced the treatment’s long-term stability after orthognathic surgery.

Cephalometric analysis is the primary diagnosis method in orthodontics. In our previous study, the algorithm was developed to estimate cephalometric landmarks from lateral facial photographs of patients with normal occlusion. This study evaluates the estimation accuracy by the algorithm trained on a dataset of 2320 patients with added malocclusion patients and the analysis values. The landmarks were estimated from the input of lateral facial photographs as training data using trained CNN-based algorithms. The success detection rate (SDR) was calculated based on the mean radial error (MRE) of the distance between the estimated and actual coordinates. Furthermore, the estimated landmarks were used to measure angles and distances as a cephalometric analysis. In the skeletal Class II malocclusion, MRE was 0.42 +/- 0.15 mm, and in the skeletal Class III malocclusion, MRE was 0.46 +/- 0.16 mm. We conducted a cephalometric analysis using the estimated landmarks and examined the differences with actual data. In both groups, no significant differences were observed for any of the data. Our new algorithm for estimating the landmarks from lateral facial photographs of malocclusion patients resulted in an error of less than 0.5 mm; the error in cephalometric analysis was less than 0.5 degrees. Therefore, the algorithm can be clinically valuable.

The maxillofacial region of patients with facial asymmetry is deformed not only in the mandible but also in the maxilla, suggesting that the head region may also be deformed. Therefore, in this study, skeletally originated mandibular prognathism with facial asymmetry was evaluated in relation to cranial morphology. The cranial morphology of patients who visited the Chiba Dental Center of Tokyo Dental College and were diagnosed with skeletal mandibular prognathism with facial asymmetry (asymmetry group: ANB 0° or less; Menton deviation 4 mm or more; 30 subjects) and without facial asymmetry (symmetry group: ANB less than 0°; Menton deviation less than 3 mm) was measured and evaluated. As a method, the length and area of the cranium were measured using axial cephalometric radiographs. In the asymmetry group, there was a significant difference in the left–right difference in the long diameter of the posterior part of the cranium compared to the symmetry group (p = 0.009). The asymmetry group also had significant differences in the central and occipital areas of the cranium on the left and right sides compared to the symmetry group (p < 0.001). In the asymmetry group, the direction of Menton deviation and the direction of head region deviation coincided in about 70% of the cases. There was also a positive correlation between head deviation and the amount of Menton deviation. The results of this study suggested that patients with facial asymmetry had greater head deformity than patients without facial asymmetry.

Arch forms in orthodontics are considered to affect occlusal stability. This study’s subjects were 47 patients (Class III S group) who visited the Chiba Dental Center of Tokyo Dental College and were surgical orthodontic cases, and 60 patients with Class I malocclusion were selected as the control group. A mandibular model of each subject was plotted with each tooth on a digitizer. The clinical bracket points of each tooth were plotted, and intercanine and intermolar measurements were taken. The least squares method was used to fit a quartic equation, and the arch form was drawn. The Class IIIS group was divided by Wits appraisal and facial pattern into a dolichofacial or brachyfacial pattern, and arch forms were compared. The results show that the Class IIIS group had a significantly smaller intermolar width, canine depth, and molar depth and a significantly larger canine W/D ratio. In those with a dolichofacial pattern, the anterior curve of the arch form tended to be flat and the posterior curve narrower. This is because, in skeletal mandibular prognathism, the mandibular anterior shows lingual tipping, and the molars show palatal tipping due to dental compensation, and it was inferred that this tendency was higher in high-angle cases.

This report describes a patient with severe high angle class II malocclusion and mandibular retrusion in whom surgical orthodontic treatment to prevent an increase in ramus height resulted in a significant improvement in esthetics and long-term stability. The patient was a woman aged 30 years 5 months who presented with the chief complaint of maxillary protrusion. She had a convex facial type, a chin button on lip sealing, and a gummy smile. Cephalometric analysis revealed a normal maxilla anterior-posterior position, but significant mandibular retrusion with pronounced clockwise rotation. The anterior maxillary tooth axis was standard, but labially inclined in the mandible. Based on these findings, the diagnosis was skeletal class II high angle malocclusion and mandibular retrusion. The proposed treatment plan comprised 2-jaw surgery with premolar extraction. Le Fort I osteotomy, in particular, was planned in the maxilla to move the ANS upward by 3.0 mm and the PNS downward by 3.0 mm. Sagittal split ramus osteotomy (SSRO) was planned to adjust the mandible and move the mandible forward by 10.0 mm. To prevent postoperative relapse, the short lingual split method was used in performing the SSRO. The mandible was split to minimize stretching of the median pterygoid muscle. Postoperatively, the ANS, PNS, and pogonion showed movement of 2.0 mm upward, 3.0 mm downward, and 8.0 mm forward, respectively. Additionally, lip closure was now natural, and the gummy smile had markedly improved. At 6 years postoperatively, there has been no change skeletally or dentally. Follow-up is being continued to monitor further progress.