TMJ disorder may be caused by a number of different conditions. An injury to the face, for example, or a bad bite, can make the temporomandibular joints and surrounding muscles work too hard. By and large, though, most cases of TMJ disorder are an issue of overuse. Some people develop uncomfortable symptoms as a result of excessive gum-chewing or from bruxism. This is the unconscious habit of clenching and grinding the teeth. It usually happens when you’re sleeping, so you may never be aware that you’re causing potential harm to your joints and teeth.