Recently, three-dimensional （3D） simulations are frequently used to predict the outcome of orthognathic surgery and treatment for jaw deformity patients. In these simulations, the maxilla/mandible and teeth are constructed from CT and STL data. These simulations can indicate the post-operative and post-treatment conditions and images, and patients can use this information to decide whether to have orthognathic treatment or not. Of course, these simulations can also provide valuable information for the team approach between oral surgeons and orthodontists.
The masticatory muscles are closely related to jaw deformity in many aspects; development of jaw deformities during the growth period, relation and interference with the mandibular bone during orthognathic surgery, and the post-operative stability and occlusion. Therefore, 3D simulations that include masticatory muscles as well as hard tissues are useful in this field. However, unlike hard tissues, simulation of muscles is not systematized by software and is not yet available for practical use in clinics. Therefore, we developed a practical system for 3D reconstruction of masticatory muscles from CT. In this review, we describe our clinical use and future aspects of 3D images of masticatory muscles.

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The patient was a 17-year-8-month-old female with Skeletal Class Ⅱ, high angle, and large overjet due to the posterior position of the mandible. Her left condyle was deformed. Temporomandibular joint disorder with deformation of the left condyle was observed, so to reduce the risk of postoperative mandibular condyle resorption, we did not perform mandibular osteotomy to move the mandible forward but performed a surgical orthodontic treatment using a combination of anterior-posterior two segment Le Fort I osteotomy and genioplasty. After treatment, a good lateral appearance and appropriate overjet and overbite were obtained, and the patient has a stable occlusion 2 years and 6 months after the start of retention.

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The number of patients with jaw deformity is increasing, and so it is necessary to train young dentists who have the knowledge, skills, and attitude required to deal with them. Aiming to improve postgraduate education on jaw deformity, we conducted a questionnaire survey to understand how trainees treat patients with jaw deformity during current dental clinical training.
The subjects of the survey were 51 dentists who graduated from the Nippon Dental University, and underwent clinical dentistry training at Niigata Hospital in 2022. A five-item questionnaire survey related to jaw deformity was conducted at the end of clinical training.
Of the clinical trainees, 66.7％ provided information on orthodontic treatment for patients with malocclusion; 68.6％ responded that they had provided information on surgical orthodontic treatment for patients with jaw deformity. Although the level of understanding of jaw deformity treatment during pre-graduate education was high at approximately 70％, the number of clinical trainees who answered that their understanding had deepened at the end of clinical training was low at 23.5％.
In clinical training for dentists, there are few opportunities to maintain and update knowledge about jaw deformities, and it is assumed that the curriculum does not cover patients with malocclusions, including jaw deformities. It is suggested that there is a need for clinical training and a lifelong training curriculum to develop dentists who can provide appropriate information to patients with jaw deformity.

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