The mouth and jaw play important roles in various functions such as eating, chewing, speaking and swallowing. However, various problems can occur if the muscles that move the jaw and mouth are subjected to excessive involuntary contraction. These problems include failure to chew foods (masticatory disturbance); problems with mouth opening (trismus) or closing; involuntary movements of the mouth, tongue, and/or lips; tremors; muscle pain; lateral shifting of the jaw (jaw deviation); and difficulties with swallowing (dysphagia) or speaking (dysarthria). Such symptoms can be caused by dystonia of the mouth and/or jaw (oromandibular dystonia), temporomandibular joint disorders, oral dyskinesia, bruxism, fibromyalgia, psychogenic movement disorder, and/or masticatory muscle tendon-aponeurosis hyperplasia. The cause of the symptoms may be one of these diseases, however more than one disease may coexist. A variety of involuntary movements can occur in the orofacial region, most of which are not diagnosed correctly. In fact, the misdiagnosis of oromandibular dystonia as temporomandibular joint disorder, psychogenic disease, bruxism, or temporomandibular joint ankylosis is very common. Most patients that are diagnosed by dentists or oral surgeons are initially treated with dental appliances. In fact, 80% of our patients with jaw closing dystonia, the most common type of oromandibular dystonia, initially visited dentists or oral and maxillofacial surgeons. None of these patients were diagnosed with dystonia. Accordingly, they did not receive appropriate treatment, and their conditions deteriorated. In addition, dental students are not taught about involuntary movements other than oral dyskinesia and bruxism, and thus, probably do not recognize the symptoms of dystonia.