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Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400 degrees C or higher. For the cobalt-chromium product the increase started at about 500 degrees C. At temperatures above 500 degrees C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires.

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Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag–Sn–Cu rich alloy powder) and a GF powder (Ag–Sn–Cu–Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag‐based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X‐ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high‐resolution electron microscopy and energy‐dispersive X‐ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag3Sn, cubic Ag9In4, tetragonal β‐Sn and hexagonal Ag2Ga. In addition to these well‐known phases Ga‐rich regions were observed consisting of an intergrowth of tetragonal CuGa2 and one of the cubic γ‐Cu9Ga4 phases. In addition to these phases cubic Ga7Pd3 was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga7Pd3.