Temporomandibular joint dysfunction (TMD or TMJD), also known as temporomandibular joint dysfunction syndrome and temporomandibular disorder among others, 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 the 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).