For more than 150 years, dentists all over the world used Dental amalgam as a filling material.
As the name implies, this material is a combination of metal alloys, silver tin and copper mixed in liquid (elemental) mercury.
The setting reaction between mercury and these metals is called an amalgamation reaction.
Wikipedia defines Dental amalgam thus:
“50% of dental amalgam is elemental mercury by weight.”
Therein lies the problem.
While minuscule amounts of mercury are ingested as the patient chews on the set filling; there is at present no scientific evidence that Mercury in amalgam fillings results in high mercury within the blood.