Mercury amalgam dental fillings: an epidemiologic assessment.

Dental amalgam fillings containing approximately 50% mercury have been used for almost 200 years and have been controversial for almost the same time. Allegations of effects caused by amalgams have involved many diseases. Recent evidence that small amounts of mercury are continuously released from amalgam fillings has fuelled the controversy. This is a comprehensive review of the epidemiologic evidence for the safety of dental amalgam fillings, with an emphasis on methodological issues and identifying gaps in the literature. Studies show little evidence of effects on general chronic disease incidence or mortality. Limited evidence exists for an association with multiple sclerosis, but few studies on either Alzheimer's or Parkinson's diseases. The preponderance of evidence suggests no renal effects and that ill-defined symptom complexes, including chronic fatigue syndrome, are not caused by amalgams. There is little direct evidence that can be used to assess reproductive hazards. Overall, few relevant epidemiologic studies are available. Most prior assessments of possible amalgam health effects have been based on comparisons of dental mercury exposures with occupational exposures causing harm. However, the amalgam-exposed population contains a broader, possibly more susceptible, spectrum of people. Common limitations of population-based studies of dental amalgam effects include inadequate longitudinal exposure assessment and negative confounding by better access to dental care in higher socioeconomic groups. Better designed studies are needed, particularly for investigation of neurodegenerative diseases and effects on infants and children.