Microstructure of dental amalgams containing high and low copper contents

Morphology and electrochemical behavior of Ag-Cu nanoparticle-doped amalgams

The aim of this study was to introduce Ag-Cu phase nanopowder as an additive to improve the corrosion behavior of dental amalgams. A novel Ag-Cu nanopowder was synthesized by the precipitation method. An amalgam alloy powder (World-Cap) was added and mixed with 5 wt.% and 10 wt.% of Ag-Cu nanopowders, respectively, to form experimental amalgam alloy powders. The original alloy powder was used as a control. Alloy powders were examined using X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy and electron probe microanalysis. Amalgam disk specimens of metallurgically prepared were tested in 0.9% NaCl solution using electrochemical methods. The changes in the corrosion potential and anodic polarization characteristics were determined. Corrosion potential data were analyzed statistically (n=3, analysis of variance, Tukey's test, p<0.05). The diameters of lamellar structure Ag-Cu nanoparticles were measured to be approximately 30 nm. The composition of the Ag-Cu nanoparticles determined by TEM-energy-dispersive spectroscopy was 56.28 at.% Ag-43.72 at.% Cu. A light-shaded phase was found mixing with dark Cu-Sn reaction particles in the reaction zones of Ag-Cu nanoparticle-doped amalgams. The Ag-Cu nanoparticle-doped amalgams exhibited zero current potentials more positive than the control (p<0.05) and no current peak was observed at -325mV that related to Ag-Hg phase and Cu6Sn5 phase in anodic polarization curves. The results indicated that the corrosion resistance of high-copper single-composition amalgam could be improved by Ag-Cu nanoparticle-doping.

Microprobe analysis of dental amalgam alloy particles of Ag-Cu eutectic composition

An electron microprobe was used to investigate the composition and microstructure of commercially available, and experimental dental amalgam alloy particles of approximately Ag-Cu eutectic composition. The method of alloy and amalgam specimen preparation and the technique used in microprobe analysis have been briefly outlined. The dispersant particles in one commercial alloy were of Ag-Cu eutectic composition (28.1% Cu), in another commercial alloy they were Cu-rich (31% Cu). Although the dispersant particles were predominantly of uniform appearance, there was evidence in some particles of an internal structure pattern, small spherical inclusions or voids. The possible composition of the Cu-rich inclusions was investigated using particles from an experimental alloy of approximately Ag-Cu eutectic composition.

Microprobe analysis of three high-copper amalgams

Three single-composition, high-copper amalgams were analyzed for the composition of their before- and after-reaction phases. The method used was electron probe microanalysis. The results may be summarized as follows: All alloys consist essentially of Ag3Sn (gamma), Cu3Sn (epsilon), and, in some cases, Ag4Sn (beta). When the original alloy contains higher amounts of Cu, more Cu is found in solution in the Ag3Sn (gamma) and Ag4Sn (beta) phases. The reaction phases in amalgams made from these alloys consist essentially of Ag22Sn Hg27(gamma 1) and Cu6Sn5 (eta'), with no detectable Sn8Hg (gamma 2). When In is present, it is found principally in the Ag3Sn (gamma) and Ag22Sn Hg27(gamma 1) phases, and both the gamma and gamma 1 phases are of different composition than that for the other alloys. When Pd is present, it is found principally in the Cu3Sn (epsilon), Cu6Sn5 (eta'), and Ag22Sn Hg27(gamma 1) phases.

X-ray diffraction analysis of gamma 2 (Sn-Hg) phase in higher copper amalgams of varying mercury content

Microstructures of high copper commercial amalgams containing varying amounts of mercury, ranging from 20% above to 25% below recommended values, were primarily investigated by x-ray diffraction. Mechanisms relating to the absence or presence of gamma 2 (Sn-Hg) phase in these amalgams were discussed in relation to the presence of copper and tin elements in their original alloys. The optimum mercury concentration in some amalgams was determined in order to keep them free of the gamma 2 (Sn-Hg) phase.

Time-dependent phase changes in Cu-rich amalgams

Cu-rich amalgams represent a significant change in amalgam alloy formulations which may result in enhanced performance. Significantly, these systems reduce or eliminate the gamma2 phase. This work studied the phase changes which occurred from one hour to six months in 13 commercial amalgams by x-ray diffraction. This included 9 two-particle or blend systems and 4 single-particle systems. Gamma2 was found in all systems, but was reduced or eliminated on storage at 37 degrees C at rates which varied from system to system. During gamma2 elimination, the Cu6Sn5 content correspondingly increased, indicating that solid-state reaction occurs for up to six months in some systems.

A study of high copper amalgams. II. Amalgamation on a Hg-plated high copper alloy containing 30 wt% Cu

The amalgamation reaction of a low silver, high copper alloy powder has been investigated by plating tablets of compacted powder with Hg. Both gamma1 Ag-Hg and micro Cu-Sn crystals form on the tablets. In spite of large differences in composition, these tablets amalgamated similarly to the T tablets studied and reported in Part I.