Usually the mechanical properties of
dental alloys are determined from the values obtained through static tests of their tensile strength, hardness, etc. Generally, high tensile strength and ductility are preferred. However, when small stresses within proportional limits are applied repeatedly (even though not amounting to destructive forces in static tests), they may cause
rupture in the
alloy or, at least, cause it to lose its original mechanical properties. This phenomenon is called
metal fatigue. It is estimated that the intraoral stress loads received by dental restorations during mastication or during insertion and removal of appliances are repeated more than 3 x 10(5) times/year. From this standpoint, it may be more appropriate to estimate the fracture strength of such
dental alloys based on the
fatigue properties of the restorative materials used for clasps, bars, and
fixed bridges. For this reason, it is necessary to obtain data through
fatigue tests on the
fatigue strength and the
fatigue endurance limits of
dental alloys, and it is important to find a correlation between these data and the static data on tensile strengths and ductility obtained by tensile tests. Two
alloys are used in these experiments. Both wrought specimens and cast specimens of 12% Au-Pd-Ag and Type III
gold alloy were prepared for the
fatigue tests. The size of the rectangular wrought specimens was 3 x 4 x 110 mm. The 12% Au-Pd-Ag
alloy was heated to 800 degrees C for 15 minutes, quenched, and reheated to 400 degrees C for 20 minutes and quenched again according to the manufacturer's instructions for heat treatment. The Type III
gold alloy was heated to 700 degrees C for 10 minutes, quenched, and reheated to 350 degrees C for 20 minutes and quenched again. The cylindrical cast specimens were 60 mm long and 2 mm in diameter. They were invested by conventional methods and cast in a centrifugal casting machine, Thermotrol Model 2500. The four point bending test for the wrought specimen was performed with a Universal
Fatigue testing machine, Shimazu UF-15 at a stress amplitude rate of 30 Hz. The cylindrical cast specimens were tested in cyclic tension in a Hydraulic IC Servo Machine, Instron Model 8501 at a gauge length of 25 mm and a stress amplitude of 10 Hz. The tensile tests for both wrought and cast specimens were performed with a Universal Testing Machine, Instron Model 1125 and measured at a cross-head speed of 1 mm/min.(ABSTRACT TRUNCATED AT 400 WORDS)