The masticatory muscles are the muscle groups associated with chewing and include the occlusal, temporal, extensor pterygoid, and internal pterygoid muscles. The muscle groups of the masticatory muscles are innervated by the trigeminal nerve. The trigeminal nerve is a mixed nerve that includes sensory and motor fibers. The trigeminal nerve is divided into ophthalmic, maxillary and mandibular branches, where the ophthalmic and maxillary branches have only sensory fibers and the mandibular branch is divided into sensory and motor branches. When the motor branch of the mandibular branch of the trigeminal nerve is diseased, weakness of the ipsilateral masticatory muscles can occur, and the patient can see a deviation of the jaw when opening the mouth. Cranial MRI and trigeminal nerve MRI should be improved to clarify the presence of vascular disease or occupational disease.