C01    Define the terms amalgam, amalgamation, dental amalgam alloys, low copper amalgams, high copper amalgams, lathe-cut powder, atomized powder, trituration, and condensation.

Amalgam = an alloy that contains mercury

Amalgamation = reaction between a metal and mercury

Dental amalgam alloy = the alloy powder that is mixed with mercury to produce a dental amalgam

Low copper amalgams = an amalgam which dental amalgam alloy contains 0-6% copper

High copper amalgams = an amalgam which dental amalgam alloy contains more than 6% copper (often 20-30% copper)

Lathe-cut powder = a dental amalgam alloy powder that has been made by grinding and milling a dental amalgam alloy until particles that are 1-40 µm have been formed.

Atomized powder = a dental amalgam alloy powder that has been made by spraying molten metal

Trituration = mixing the dental amalgam alloy powder with the mercury

Condensation = after insertion of the plastic amalgam into the cut cavity, the material is packed into the cavity with a condenser

Composition of Dental Amalgam Alloys

Traditional dental amalgam alloys come as either lathe-cut or atomized (spherical) particles consisting mainly of Ag₃Sn and smaller amounts of elements such as copper and zinc. The lathe-cut alloys of this composition has been used from the late 19^th century, while the spherical particles have been available since 1962.

Admixed high-copper dental amalgam alloys consist of a mixture of a lathe-cut powder (Ag₃Sn) and a spherical Ag-Cu (eutectic composition) powder. The original idea was to use the Ag-Cu particles as reinforcing particles, but the main benefit was that in this amalgam no gamma-2 phase (Sn_7-8Hg) was formed during setting. These amalgams have been available since 1963.

Spherical high-copper dental amalgam alloys were develop to solve a problem associated with the admixed high-copper dental amalgam alloys. This problem was that the two particle types present in the admixed dental amalgam alloys separated during storage of the powder. By melting silver-tin-copper and spraying the molten alloy into small spheres, it was possible to produce spheres containing both Ag₃Sn and Cu₃Sn in each spheres. These spheres when mixed with mercury formed an amalgam that was also free from the gamma-2 phase. These dental amalgam alloys were introduced in 1967.

Shapes of Dental Amalgam Alloy Particles

Important knowledge

Both dental amalgam alloy particle shape and composition determine the properties of the amalgam.

Spherical dental amalgam alloy particles require less mercury, lower condensation pressure because of their lower "internal friction" and produce amalgams that set faster than those containing lathe-cut particles.

High-copper amalgams do not contain the corrosion prone gamma-2 phase (Sn_7-8Hg). Because of the latter the high-copper amalgams have superior marginal stability. The high-copper amalgams should be used rather than the low-copper amalgams (also called "traditional" or "conventional").