Review of temporomandibular joint pathology. Part I: classification, epidemiology and risk factors.

Pathology of the temporomandibular joint (TMJ) affects an important part of the population, though it is not viewed as a public health problem. Between 3-7% of the population seeks treatment for pain and dysfunction of the ATM or related structures. The literature reports great variability in the prevalence of the clinical symptoms (6-93%) and signs (0-93%), probably as a result of the different clinical criteria used. In imaging studies it is common to observe alterations that have no clinical expression of any kind. Radiographic changes corresponding to osteoarthrosis are observed in 14-44% of the population. Age is a risk factor, though with some particularities. In elderly patients there is an increased prevalence of clinical and radiological signs, though also a lesser prevalence of symptoms and of treatment demands than in younger adults. Approximately 7% of the population between 12 and 18 years of age is diagnosed with mandibular pain-dysfunction. Temporomandibular dysfunction (TMD) is more frequent in females. No clear relationship has been established between occlusal alterations and TMJ disease. Only disharmony between centric relation and maximum intercuspidation, and unilateral crossbite, have demonstrated a certain TMJ disease-predictive potential. Both local and systemic hyperlaxity has been postulated as a possible cause of TMD. Parafunctional habits and bruxism are considered risk factors of TMD with odds ratios (ORs) of up to 4.8. Psychophysiological theory holds stress as a determinant factor in myofascial pain. Genetic factors and orthodontic treatment have not been shown to cause TMD.