High copper alloys for dental amalgam.
The nature, physical properties and clinical performance of amalgams made from alloys containing copper in excess of 6 per cent by weight are reviewed. There are two basic types of high copper alloy: (a) mixtures of 'spherical' silver/copper or silver/tin/copper particles with low copper low copper lathe-cut or 'spherical' and (b) single composition silver/tin/copper spherical or lathe-cut particles. Copper contents range from 8.5 per cent to 30 per cent. In amalgams made from high copper alloys the soft corrodible gamma 2 (Sn7Hg) phase is reduced or eliminated by preferential formation of the eta (Cu6Sn5) phase. Improved clinical performance (less marginal breakdown) has been related to low creep, little or no gamma 2 phase and the presence of zinc. The possible roles played by these factors in the mechanism of marginal breakdown are discussed. Physical properties are not a reliable guide to the clinical performance of amalgams. Although high copper amalgams as a group show 'superior' physical properties and clinical performance to low copper amalgams, a high copper content does not necessarily mean improved clinical performance. Indeed, certain well-manipulated low copper amalgams can show clinical results comparable with some high copper amalgams, but not as good as the best high copper amalgams. In most clinical studies the silver/copper plus lathe-cut (dispersed phase) alloys and some of the single composition high copper alloys show the greatest clinical durability. The most significant factor in clinical performance is the choice of alloy.
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003300:Copper / Q000032:analysis; D003343:Corrosion; D003722:Dental Alloys / Q000032:analysis; D003723:Dental Amalgam; D010316:Particle Size; D013314:Stress, Mechanical
D003722:Dental Alloys; D003300:Copper; D003723:Dental Amalgam