localized, and intermittent, although it can sometimes be constant. The pain is more usually unilateral (located on one side) rather than bilateral. It is rarely severe. Limited range of mandibular movement, which may cause difficulty eating or even talking. There may be locking of the jaw, or stiffness in the jaw muscles and the joints, especially present upon waking. There may also be incoordination, asymmetry or deviation of mandibular movement. Noises from the joint during mandibular movement, which may be intermittent. Joint noises may be described as clicking, popping, or crepitus (grating). TMJ dysfunction is commonly associated with symptoms affecting cervical spine dysfunction and altered head and cervical spine posture. Other signs and symptoms have also been described, although these are less common and less significant than the cardinal signs and symptoms listed above. Examples include: Headache (possibly), e.g. pain in the occipital region (the back of the head), or the forehead; or other types of facial pain including migraine, tension headache. or myofascial pain. Pain elsewhere, such as the teeth or neck. Diminished auditory acuity (hearing loss). Tinnitus (occasionally). Dizziness. Sensation of malocclusion (feeling that the teeth do not meet together properly). Causes TMD is a symptom complex (i.e. a group of symptoms occurring together and characterizing a particular disease), which is thought to be caused by multiple, poorly understood factors, but the exact etiology is unknown. There are factors which appear to predispose to TMD (genetic, hormonal, anatomical), factors which may precipitate it (trauma, occlusal changes, parafunction), and also factors which may prolong it (stress and again parafunction). Overall, two hypotheses have dominated research into the causes of TMD, namely a psychosocial model and a theory of occlusal dysharmony. Interest in occlusal factors as a causative factor in TMD was especially widespread in the past, and the theory has since fallen out of favor and become controversial due to lack of evidence. Disc displacement In people with TMD, it has been shown that the lower head of lateral pterygoid contracts during mouth closing (when it should relax), and is often tender to palpation. To theorize upon this observation, some have suggested that due to a tear in the back of the joint capsule, the articular disc may be displaced forwards (anterior disc displacement), stopping the upper head of lateral pterygoid from acting to stabilize the disc as it would do normally. As a biologic compensatory mechanism, the lower