Many blended or dispersed phase high Cu amalgams show excellent clinical performance in long term clinical trials. However, little is known concerning the microstructural changes that occur during clinical use of these systems. This investigation sought to characterize some of the changes that occur in the Ag-Cu particles and their surrounding reaction zones based on a study by backscattered scanning electron microscopy (BSEM), energy dispersive spectroscopy and a new rnicroprobe technique called Colorad which assigns various colors to elements and element combinations and indicates changes in elemental concentration by changes in color value (brightness). Restorations were retrieved from clinical trials and compared to control restorations prepared and retrieved in the same way. The clinical restorations showed marked changes in the composition of the Ag-Cu particles with the composition approaching that of the surrounding matrix phase so that they appear as pale particles in BSEM. These particles were often surrounded by a ring of Sn-rich corrosion product which replaced the normal reaction zone. The reaction zones appeared to be complex and have a number of subzones of varying composition. Many of the reaction zones also underwent coarsening of their structure. Corrosion is thought to play a prominent role in the conversion of the Ag-Cu particles to a Ag-Hg composition similar to the surrounding matrix. There appeared to be more transformation in the L system, a dispersed phase system without Zn, which has poorer clinical survival, than in the D system, a dispersed phase system with 1 % Zn, which shows superior clinical performance.
Marshall, Grayson W. Jr.; McCoy, D. D.; Kinney, John H.; Letzel, Hugo; and Marshall, Sally J.
"Microstructural Changes in Retrieved Amalgam Restorations,"
Cells and Materials: Vol. 2
, Article 4.
Available at: http://digitalcommons.usu.edu/cellsandmaterials/vol2/iss1/4