A comparison of the tensile and bending properties of dental gold wires.

M ODERN dental practice makes wide use of precious metal alloys in wire form as partial denture clasps and as orthodontic appliances. When used in such applications, these alloys are subject only to bend loading and never to pure tensile loading. For this reason, there has long been a feeling within the dental profession that the tensile test for wires was somewhat inappropriate and might be replaced advantageously by a bend test. However, the absence of any previous correlation between the test values obtained from the two types of loading, as well as the large amount of effort represented by collected tensile data on these alloys, has heretofore prevented any serious consideration of a possible change of standards from one test to the other. The technical representatives of several manufacturers have displayed a continuing interest in the development of possible relationships between tension and bend tests. This interest was expressed through the loan, by these manufacturers, of gold alloy wires of high intrinsic value for use in this investigation. Further support was received from the Office of Naval Research which sponsored the project as a part of its program of research on the properties of restorative dental materials. The specific purpose of this investigation was to determine what correlation, if any, existed between the mechanical properties of wrought gold alloys as found in a standard tensile test and those as found in a bend test. The type of bend test used in this investigation was the cantilever loading of a wrought gold wire. It is believed that the conditions of such a bend test much more nearly approach the actual conditions under which these alloys are used than does the tensile test. The program of the project was set up as follows: An attempt was made to obtain a wide range of inherent mechanical properties in the alloys to be tested, at the same time reducing as far as possible other variables such as wire size, sample length, and heat treatment. A total of twelve alloys was selected, all of the same size and all to be subjected to identical heat treatment and testing. These alloys were to be tested in two conditions, fully soft (10 min. at 7000 C., quench), and age hardened (softened as above, then 15 min. at 360° C.). It was recognized that this hardening practice might not produce either the maximum or optimum properties of any one alloy, but it was