Does amalgam affect the immune system? A controversial issue.

Although in use for more than 150 years, dental amalgam has been questioned more or less vigorously as a dental restoration material due to its alleged health hazard. Humans are exposed to mercury and the other main dental amalgam metals (Ag, Sn, Cu, Zn) via vapour, corrosion products in swallowed saliva, and direct absorption into the blood from the oral cavity. Dental amalgam fillings are the most important source of mercury exposure in the general population. Local, and in some instances, systemic hypersensitivity reactions to dental amalgam metals, especially mercury, occur at a low frequency among amalgam bearers. Experimental and clinical data strongly indicate that these and other subclinical systemic adverse immunological reactions to dental amalgam metals in humans will be linked to certain MHC genotypes, and affect only a small number of the exposed individuals. These individuals will be very difficult to detect in a mixed population of susceptible and resistant individuals, including persons with alleged symptoms due to dental amalgam fillings, where many of the individuals are likely to suffer from conditions with no proven immunological background such as multiple chemical sensitivity syndrome. Intensified studies should be performed to identify such susceptible MHC genotypes, taking advantage of the reported cases of more heavily metal-exposed humans with systemic autoimmune reactions. Further studies will also be needed to ascertain whether the combined exposure to the metals in dental amalgam may lower the threshold for adverse immunological reactions, since recent studies have shown that the metals in alloy, especially silver, may induce autoimmunity in genetically susceptible mice.