"The use of dental amalgam as a restorative material has long been a contentious issue because of its elemental mercury component. While microleakage of mercury from amalgam has been conclusively confirmed over the past 30 years intensive research has failed to identify deleterious health outcomes. Mercury, as with other metals entering the body tissues, appears to be tolerated at low levels. Nevertheless, a contrary opinion is held by some professional and lay groups who advocate a zero tolerance for inhaled or ingested elemental mercury. They identify dental amalgam as an aetiological factor for neurological conditions such as chronic fatigue syndrome, multiple sclerosis and Alzheimer's disease resulting from chronic mercury poisoning. Epidemiological and clinical evidence of widespread chronic mercury toxicity associated with a body burden of amalgam has consistently failed to be established even in populations with a high prevalence of dental amalgam restorations. On current evidence, international consensus heavily supports the statement that amalgam does not constitute a health risk to patients. However, exposure to volatile free mercury in dental clinics should be controlled to eliminate occupational risk."
So the opionion of the dentists is: There is no health risk. The biggest risk may be to have all the amalgam replaced because this might actually cause some type of intoxication.
More information about wrong assumptions concerning amalgam at the great Quackwatch-webpage