C03    Discuss the composition of high copper amalgams and contrast admixed and single composition alloys.

Admixed High-Copper Dental Amalgam Alloy Powder

As seen from the above table, the admixed high copper amalgam alloy contains both lathe-cut and spherical particles. The lathe-cut particles have the same composition as the traditional low copper dental amalgam alloys, while the spherical particles consist of the eutectic Ag-Cu composition. The original idea was that the spherical particles would dispersion strengthening the conventional amalgam. This improvement, though, was not significant. Instead it was found that the set admixed high-copper amalgam did not contain the corrosive gamma-2 phase (g₂ ), and consequently, the marginal fracture frequency of these amalgams was lower than that of the traditional amalgam.

Spherical (single composition) High-Copper Dental Amalgam Alloy Powder

As seen from the above table, the spherical dental amalgam alloy particles consist of a single particle composition. What is not shown from the table is that each particle contain two phases, the Ag₃Sn and the Cu₃Sn. These alloys do not need any zinc, since they are atomized inside a container filled with an inert gas.

Comparing the two high-copper dental amalgam alloys show that they during setting deliver copper from different phases. The eutectic Ag-Cu particles release copper in the admixed amalgam, while the Cu₃Sn particles is the copper source in the spherical high-copper amalgams.