Dental amalgam

An amalgam is an alloy composed of mercury and other metals. Dental amalgam is produced by mixing liquid mercury with an alloy made of silver, tin, and copper solid particles. Small quantities of zinc, mercury and other metals may be present in some alloys. This combination of solid particles is known as amalgam alloy. The composition of the alloy particles are controlled by the ISO Standard (ISO 1559) for dental amalgam alloy in order to control properties of set amalgam such as corrosion and setting expansion. It is important to differentiate between dental amalgam and the amalgam alloy that is commercially produced and marketed as small filings, spheroid particles, or a combination of these, suitable for mixing with liquid mercury to produce the dental amalgam. Amalgam is used most commonly for direct, permanent, posterior restorations and for large foundation restorations, or cores, which are precursors to placing crowns.

The reaction between mercury and alloy when mixed together is termed an amalgamation reaction. It will result in the formation of silver-grey workable mass which can be condensed into cavities. After condensing, the dental amalgam is carved to generate the required anatomical features and then hardens with time. In the pre-1986, the standard composition of alloy is referred to as conventional amalgam alloy. More recently (post-1986), there have been a change in the compositional standard of the alloy due to better understanding of structure-property relationships for the materials. Conventional amalgam alloy commonly consists of silver (~65% ), tin (~29%), copper (~8%) and other trace metals. While current amalgam alloy consists of silver (40%), tin (32%), copper (30%) and other metals.

Dental amalgams were first documented in a Tang Dynasty medical text written by Su Kung in 659, and appeared in Germany in 1528. In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability.

Concern for appearance, environmental pollution, health, and the availability of improved, reliable, composite materials have diminished its popularity. In addition, amalgam restorations are brittle and susceptible to corrosion. In particular, concerns about the toxicity of mercury have made its use increasingly controversial. However, dental amalgam is a highly successful restorative material and cost effective.

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