A dental filling is a way to restore a damaged or  decayed tooth back to its normal function and shape. When a dentist gives you a filling, they first remove the decayed tooth by using a drill to clean 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 gold, porcelain, a composite resin (tooth-colored fillings), and an amalgam (an alloy of mercury, silver, copper, tin and sometimes zinc).