Temporomandibular disorders: Definition and etiology

Temporomandibular disorders (TMDs) are a group of musculoskeletal conditions affecting the masticatory system and which are best defined based on symptoms and signs reflective of the underlying disease process. Etiology – the cause of disease – is best considered as risk determinants due to the complexity of TMDs in terms of the broad range of factors that place an individual at risk for initial development of a TMD and at risk for transition from an acute disorder to a chronic disorder. Identified risk determinants act together in unique patterns across individuals; notably, painful TMDs seldom occur in isolation of other risk determinants. While occlusal characteristics have been proposed as a primary etiology for TMDs, the evidence remains weak and unconvincing. In contrast, the evidence is strong for a wide range of intersecting factors to act as risk determinants for initial onset of a painful TMD, and which contribute further when pain becomes chronic due to bidirectional relationships between a primary pain condition and its risk determinants. These include overuse behaviors, pain sensitivity, psychological distress, injury, and the presence of other health and pain disorders. Overall, the evidence points to TMDs as system level disorders residing within a person at risk due to any of these identified risk determinants, and when more than one is present, the risk increases substantially. This complexity requires evolved standards of care for evaluation and treatment of the identified risk determinants based on available evidence.