Involuntary movement is defined as movement that is not under the control of the brain. Movement disorders are neurological conditions that affect the speed, fluency, quality, and/or ease of movement. Abnormal fluency or speed of movement might manifest as excessive or involuntary movement, or slow or absent voluntary movement. There are various kinds of involuntary movements, e.g., dyskinesia, dystonia, tics, tremors, athetosis, myokymia, myoclonus, and chorea. The causes of involuntary movements remain unclear. However, dystonia is considered to be caused by functional abnormalities of the basal ganglia, which controls movement and posture, and can also develop in patients who have been taking oral psychiatric drugs for long period. The symptoms of dystonia are often observed after dental treatment (insertion of a new denture, tooth extraction, etc.) or a trauma involving the jaw or mouth. However, even though dental care can trigger the condition it does not directly cause it. Dystonia patients who experience mouth-related symptoms caused by involuntary contractions of the muscles of the jaw and/or tongue, particularly when they try to speak, often have professions that require them to speak regularly such as receptionists, sales staff, announcers, and teachers. Talking in a very stressful state for a long period of time can also contribute to dystonia and could be considered to be a kind of occupational dystonia, which is a type of dystonia in which the same movement is repeated excessively during a particular occupation, e.g., by a musician or craftsman causing muscle cramps.