Fretting-fatigue properties and fracture mechanism of semi-precious alloy for dental applications

Dental Ag-Pd-Cu-Au-Zn system alloy, which is a semi-precious alloy, is one of the most widely used metallic dental materials in Japan due to its excellent mechanical properties and corrosion resistance and applicability to health insurance. Dental products, e.g., inlays and crowns, fabricated from this alloy are used under cyclic loading conditions including frictional wear, when it comes in contact with the same or other dental materials in the oral cavity or an opposing tooth during mastication. The effects of microstructures of Ag-20 mass% Pd-14.5 mass%Cu-12 mass%Au-2 mass%Zn alloy on the fretting-fatigue properties are, therefore, investigated in this study. The fretting-fatigue strength of the Ag-20 mass%Pd-14.5 mass%Cu-12 mass%Au-2 mass%Zn alloy subjected to solution treatment (ST) and aging treatment (AT) decreases significantly as compared to the fatigue strength without fretting (plain-fatigue strength). Moreover, the fretting-fatigue strength after the AT decreases by approximately 60% as compared to that after the ST, especially in the high-cycle fatigue life region. Several traces of fretting wear are observed to be distributed in the slip region of both materials. These wear traces are generated due to the accumulation of wear debris on the fretting pad or the fretting fatigue specimen. These traces of fretting wear are distributed more closely in the slip region of the AT material. Therefore, the fatigue life decreases significantly because the fretting fatigue crack initiation life and the propagation life decrease in the AT material.