Amalgam is dental filling material used to fill cavities caused by tooth decay.Dental amalgam is a mixture of metals, consisting of liquid mercury and a powdered alloy composed of silver, tin, and copper. Approximately 50% of dental amalgam is elemental mercury by weight.Dental amalgam fillings are also known as “silver fillings” because of their silver-like appearance.

When placing dental amalgam, the dentist first drills the tooth to remove the decay and then shapes the tooth cavity for placement of the amalgam filling. Next, under appropriate safety conditions, the dentist mixes the powdered alloy with the liquid mercury to form an amalgam putty.  This softened amalgam putty is placed in the prepared cavity, where it hardens into a solid filling.

Dentists use amalgam ("silver") tooth fillings because they're strong and they last a long time -- typically at least seven years, and usually longer. They also are the least expensive type of fillings. Dental amalgam is a mixture of metals; the fillings are known as silver fillings because of their silver color. Dentists often use them for fillings in the back teeth.