In dentistry, amalgam is an alloy of mercury used to fill teeth cavities. It is made by mixing a combination of liquid mercury and particles of solid metals such a silver, copper or tin. The amalgam is mixed by the dentist just before use. It remains soft for a short while after mixing, which facilitates it being snugly packed into the cavity and shaped before it sets hard.

Mercury is a chemical element; it has symbol Hg and atomic number 80. It is also known as quicksilver and was formerly named hydrargyrum from the Greek words hydor (water) and argyros (silver). A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure; the only other element that is liquid under these conditions is the halogen bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.