A filling is a way to restore a tooth damaged by decay back to its normal function and shape. When a dentist gives you a filling, he or she first removes the decayed tooth material, cleans the affected area, and then fills the cleaned out cavity with a filling material. By closing off spaces where bacteria can enter, a filling also helps prevent further decay.
Materials used for fillings include a composite resin (tooth-colored fillings), an amalgam (an alloy of mercury, silver, copper, tin and sometimes zinc), and sometimes porcelain.