In simple cases of jaw deformity without yaw correction, conventional cephalometric prediction works well. However, patients with yaw deformity require analyses with 3D models or 3D virtual simulation. In most cases of facial asymmetry, even if 3D analyses are performed, hard tissue simulation alone does not provide a satisfactory outcome. We therefore propose yaw correction based on soft tissue simulation to overcome this problem. Our major correction strategy is based on cephalometric analysis with an enormous amount of accumulated knowledge, and soft tissue virtual simulation covers the weak points. Although the accuracy of virtual soft tissue prediction does not reach the level of the actual use of postoperative prediction , soft tissue evaluation of virtual yaw correction might provide a better vector to obtain better facial contour. Further research is needed before virtual soft tissue simulation is used for soft tissue prediction.
Optimal reproduction of this simulation technique in the operative field is necessary to successfully use this procedure. European researchers invented interactive visualizing displays to reposition the maxilla into the simulated position . However, they were unrealistic for routine orthognathic surgery and were extremely time-consuming and costly. Owing to recent improvement and popularization of 3D printers, various types of surgical stents with CAD/CAM for positioning of bone segments as well as osteotomy guides have been reported [6, 8, 9]. Although they require less time and cost, a certain amount of manpower and money are also necessary to design and manufacture these complex structures.
The CAD/CAM splint we used is custom-made by a manufacturer. The manufacturer also performs laser-scanning of plaster dental models. The operators must only perform virtual simulation and fusion between the jaw simulation and dental arch data. Our technique combines the CAD/CAM splint and a simple intraoperative positioning device, thus using the least cost and time to achieve the desired outcome. Additionally, it is possible to achieve upward and backward repositioning of the maxilla without bony interference; this is often needed in cases of facial asymmetry. The accuracy and reliability of the combination of the positioning device and horseshoe osteotomy have been reported elsewhere .