acupuncture is best employed as an adjuvant to other treatments in TMD. However, some suggest that acupuncture may be no more effective than sham acupuncture, that many of the studies investigating acupuncture and TMD have significant risk of bias, and that the long term efficacy of acupuncture for TMD is unknown. Chiropractic Chiropractic adjustments (also termed manipulations or mobilizations) are sometimes used in the belief that this will treat TMD. Related conditions that are also claimed to be treatable by chiropractic include tension headaches and neck pain. Some sources suggest that there is some evidence of efficacy of chiropractic treatment in TMD, but the sources cited for these statements were case reports and a case series of only 9 participants. One review concluded "inconclusive evidence in a favorable direction regarding mobilization and massage for TMD". Overall, although there is general agreement that chiropractic may be of comparable benefit to other manual therapies for lower back pain, there is no credible evidence of efficacy in other conditions, including TMD. However, there is some evidence of possible adverse effects from cervical (neck) vertebral manipulation, which sometimes may be serious. Prognosis It has been suggested that the natural history of TMD is benign and self-limiting, with symptoms slowly improving and resolving over time. The prognosis is therefore good. However, the persistent pain symptoms, psychological discomfort, physical disability and functional limitations may detriment quality of life. It has been suggested that TMD does not cause permanent damage and does not progress to arthritis in later life, however, degenerative disorders of the TMJ such as osteoarthritis are included within the spectrum of TMDs in some classifications. Epidemiology TMD mostly affects people in the 20 – 40 age group, and the average age is 33.9 years. People with TMD tend to be younger adults, who are otherwise healthy. Within the catchall umbrella of TMD, there are peaks for disc displacements at age 30, and for inflammatory-degenerative joint disorders at age 50. About 75% of the general population may have at least one abnormal sign associated with the TMJ (e.g. clicking), and about 33% have at least one symptom of TMD. However, only in 3.6–7% will this be of sufficient severity to trigger the individual to seek medical advice. For unknown reasons, females are more likely to be affected than males, in a ratio of about 2:1, although others report this ratio to be as high as