Mercury in dental amalgam: a risk analysis

Mercury is a highly potent cell toxin with effects on human and animal nervous systems. Mercury vapour released from dental amalgam is the predominant source of mercury in the human adult and foetal central nervous system in populations of developed countries. Only in small populations with high consumption of methyl mercury containing fish can the contribution from fish consumption reach or surpass that of amalgam fillings. The most severe health risk is that of interference with foetal and child brain development. This effect of mercury vapour exposure has been demonstrated in animal experiments on monkeys and rats and in nerve cell cultures at nanomolar concentrations. The effect is also supported by epidemiological studies on women occupationally exposed to mercury vapour during pregnancy. However, there is no data permitting an assessment of dose-response relations for this effect in humans. In epidemiological studies on populations with occupational exposure to mercury vapour, subclinical effects on kidneys, the immune system, thyroid function, and CNS function have been observed at an exposure level equal to the upper range of the exposure range seen in amalgam bearers and measured as urine excretion rate of inorganic mercury. The cell toxic effect of mercury is likely to be based on the ability of mercury to modify protein tertiary and quaternary structure. As protein structure is genetically determined, there is ample scope for genetic polymorphism to manifest itself in varying sensitivity and reaction to mercury exposure. It is also likely that mercury exposure from dental amalgam exerts side effects like most potent pharmaceuticals. The clinical support for this assumption is reviewed. An incidence of side effects exceeding 10% is unlikely considering available epidemiological evidence. However, an incidence of 1% or below is highly probable. It is recommended that use of amalgam for dental restorations is abandoned and substituted with available less toxic material and that amalgam restorations in children and women of childbearing age should be avoided due to the potential risk of interference by mercury with brain development.