No heritability of temporomandibular joint signs and symptoms

The causes of temporomandibular joint (TMJ)-related signs and symptoms are largely unknown. We tested the hypotheses that these signs and symptoms, as well as oral parafunctional habits, are substantially heritable. Questionn aire and clinical data were collected from 494 twins, including pairs of re ared-apart and reared-together monozygotic (MZ) and dizygotic (DZ) twins. A history of joint-area pain, joint noises, and clenching and grinding habit s was scored as present or absent. Twenty-nine percent of the population ex perienced at least one sign or symptom. Nearly one-quarter of subjects clen ched or ground their teeth, and 8.7% reported a history of joint-area pain. Pain was associated with clenching, grinding, sind joint noises. MZ twins were no more similar than DZ twins for any outcome, suggesting that genetic factors do not influence these traits in the population. Reared-together M Z twins were no more similar than reared-apart MZ twins, suggesting a negli gible effect of the family environment on these outcomes. Environmental fac tors unique to each twin appeared to be the major determinants of variation in this population.