It is often difficult to determine the actual cause of this disorder. Sometimes excessive strain is the main cause of symptoms related to chewing, swallowing, and speaking. It is possible that this strain is caused by bruxism. Essentially, this is the result when you grind or clench your teeth involuntarily and habitually. However, TMJ can be caused by trauma to the jaw, head, or neck. TMJ pain can also be caused by arthritis and disk displacement in the jaw joint. The pain of TMJ may also be aggravated or overlapped by fibromyalgia or irritable bowel syndrome.