amalgam

An amalgam is an alloy that contains mercury as a constituent. The mercury forms with other metals at room temperature, producing a material that is often more pliable and dense than the constituent metals alone. In chemistry, amalgams describe any mercury-containing alloy; in dentistry, the term refers to a specific filling material used to restore decayed teeth.

Dental amalgam typically comprises about 50% elemental mercury by weight and a powdered alloy of silver, tin, copper, and sometimes zinc. The powder reacts with mercury to form a hard, durable restoration that is resistant to chewing forces. Advantages include low cost, ease of placement, and longevity. Disadvantages include the metallic appearance and, for some, concerns about mercury exposure. The mercury content is largely immobilized in the set material and current guidelines indicate minimal health risk when used as directed, though some populations prefer alternatives.

Amalgamation is also used to extract metals from ores, especially the processing of gold and silver. In historic gold mining, mercury forms an amalgam with metallic gold; the amalgam is then heated to release gold and evaporate mercury. This method is being phased out or tightly controlled because of mercury pollution and health risks.

In materials science, dental amalgams have evolved; high-copper amalgams reduce the gamma-2 phase that predisposes to corrosion and marginal breakdown, improving strength and longevity. Environmental and occupational health concerns have led to regulation and cautions about mercury handling and dental waste.