Temporomandibular disorders (TMD) are a diverse group of disorders that are characterized by pain specific to the jaws. These disorders may be divided into the following primary groups: those related to the muscles acting on the joint (myofascial) and those related to the joint itself (ar-throgenic). TMD may be associated with headache, peri-auricular pain, neck pain, decreased jaw excursion, locking episodes, and noisy joint movement ("clicking" or "popping" sounds). The pain of TMD may be unilateral or bilateral. Epidemiologic data on TMD is difficult to accurately measure because its symptoms are variable and there are no universally accepted specific diagnostic criteria. TMD is believed to be the most common cause of facial pain after toothache. It may be present in 10% of the population at any given point in time, and approx 25% to 30% of the population will seek medical care for TMD during their lifetimes. TMD afflicts young adults between the ages of 20 and 40 years and females more frequently than males.
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