Amalgam allergies are extremely rare reactions to the mercury used in the most popular form of dental filling.  The condition is so unusual that fewer than 100 cases have ever been reported, according to the American Dental Association.

Amalgam has been used for more than 150 years to repair teeth damaged by decay. The amalgam itself is a mixture of equal parts liquid mercury and alloy powder containing silver, tin, and copper. Sometimes, lesser amounts of zinc, palladium or indium also are used. Mercury is the only element known to bind together these metals in a way that can be used to fill a cavity (a small hole in a tooth caused by tooth decay).

Dentists long have preferred working with amalgam because of its relatively low sensitivity to moisture, such as saliva. This means dentists do not have to be quite as precise when placing amalgam, as it is more durable and “forgiving” than other substances used in tooth repair.  

An amalgam allergy occurs when the immune system becomes sensitized to a component in amalgam and then mistakes the substance as a foreign invader. The immune system then attacks the substance, producing symptoms of an allergic reaction (e.g., skin rash, itching). The substance in amalgam that is a potential trigger for this allergic reaction (allergen) is liquid mercury. Individuals with this condition must have other restorative materials (e.g., resin, porcelain, gold) used on them during dental procedures.

Patients who suffer amalgam allergies typically have a personal history or family history of allergies to metals.