Temporomandibular joint dysfunction (sometimes abbreviated to TMD or TMJD and also termed temporomandibular joint dysfunction syndrome, temporomandibular disorder or many other names), is an umbrella term covering pain and dysfunction of the muscles of mastication (the muscles that move the jaw) and the temporomandibular joints (the joints which connect the mandible to the skull). The most important feature is pain, followed by restricted mandibular movement, and noises from the temporomandibular joints (TMJ) during jaw movement. Although TMD is not life-threatening, it can be detrimental to quality of life, because the symptoms can become chronic and difficult to manage. About 20% to 30% of the adult population are affected to some degree. Usually people affected by TMD are between 20 and 40 years of age, and it is more common in females than males. TMD is the second most frequent cause of orofacial pain after dental pain (i.e. toothache). TMD is a symptom complex rather than a single condition, and it is thought to be caused by multiple factors. However, these factors are poorly understood, and there is disagreement as to their relative importance. There are many treatments available, although there is a general lack of evidence for any treatment in TMD, and no widely accepted treatment protocol exists. Common treatments that are used include provision of occlusal splints, psychosocial interventions like cognitive behavioural therapy, and medications like analgesics (pain killers) or others. Most sources now agree that no irreversible treatment should be carried out for TMD.