Amalgam Fillings

Silver Amalgams:

Silver amalgam has been used to fill the cavities made by dentists during the removal of dental decay from teeth. When pure silver is mixed with mercury it produces a paste of slowly forming intermetallic compounds. When this is packed into the cavity at body temperature, the intermetallic compounds interlock and the amalgam hardens. However, setting is accompanied by a considerable expansion, and 100 years ago it was discovered that this can be controlled by adding tin to the silver. Unfortunately, this produces corrodible tin-mercury intermetallic phases, and their loss can cause breakdown of the filling. By adding copper, the tin-mercury phase is eliminated and modern dental amalgams are made by mixing silver-tin-copper alloy powder with mercury. This results in fillings that resist both the mechanical and chemical onslaughts within the mouth for many years. Although the amount of mercury lost from such fillings is like the contamination of a drink by a drowning midge, those determined to deny the benefits of having usefully restored teeth have over emphasised the risk, and this has generated a search for an alternative, metallic, mercury-free, filling material.