The current precious metal dental alloys are apt to contain base metal additions that tend to "fire refine" out of the alloy. In the set of representative alloys examined, the copper and silver contents remained relatively stable. Iron oxidized out severely using torch or induction melting; it oxidized out mildly using resistance furnace melting. New metal additions to the charge can offset the base metal losses.

Mechanical and heat treatment characteristics of two nickel-chromium-based dental casting alloys were investigated. Both alloys showed rapid response to heat treatment. In their softened state the alloys lost 25 to 50% of their as-cast hardness. Elongation was 20 to 45%. Rehardening nearly restored as-cast strength, whereas elongation values remained at 10 to 17%.In recent years base metal alloys have almost replaced gold in the fabrication of large dental appliances and have made inroads with the smaller castings through the porcelain-fused-to-metal restoration. The main problems with the base metal alloys can be associated with their excessive hardness and inadequate elongation. Modification of the properties of cobalt-chromiumand of cobalt-nickel-chromium-based alloys through heat treatment, compositional alterations, and variations in investing and casting techniques have been described by other authors.1-8 Little information is available, however, regarding the properties of the newer nickel-chromium-based casting alloys.The purpose of this study was to investigate heat treatment effects on the mechanical properties of two commercial nickelchromium-based alloys,* to define critical treatment parameters such as heat treatment temperature and time, and to suggest practical application of the experimental results.

No abstract

No abstract