Amalgam (dentistry) packs the plastic mass, before it sets, into the cavity. The amalgam expands ≈0.1% over 6–8 hours on setting. The final structure is a metal matrix composite, where γ, η and γ phases, are a matrix for unreacted original alloy, minus the fast-reacting β-phase and excess Sn. Amalgam is a mixture of two or more metals (alloy) with mercury which has been purified first by distillation to remove impurities. Currently, major components of the alloy are silver tin and copper. The composition of the alloy powder is controlled by ISO standard for dental amalgam alloy (ISO 1559) to control the
Amalgam (dentistry) problem. This phase has been shown to be the weakest phase in the set amalgam and is subject to corrosion, particularly at the tooth-amalgam interface. In 1962 a new amalgam alloy, called Dispersalloy, was introduced with the addition of a spherical silver-copper eutectic particle to the traditional lathe-cut AgSn particle in a ratio of 1:2. The mixture of these two types of particles is known as admix alloy. The benefits of this alloy was to strengthen the set amalgam and reduce the γ phase (SnHg). The increased copper in the silver-copper eutectic reacted preferentially with tin so that SnHg could