Deflection fatigue of cobalt-chromium, titanium, and gold alloy cast denture clasp

The aim of this study was to determine the fatigue resistance of the cast clasps of removable partial dentures. The different commercial types of metals used included five cobalt-chromium alloys, pure titanium, one titanium alloy (Ti-6A1-4V) and one gold alloy (type IV) that was either unhardened or age-hardened (n = 5 per group). The test method used was a constant-deflection fatigue test in which the force required to deflect the clasp for 0.6 mm and the number of loading cycles required to fracture the clasp were determined. The fatigue fracture surface of the clasps was examined with a scanning electron microscope. The results revealed that a fatigue fracture occurred in the cobalt-chromium clasp after approximately 25,000 loading cycles, in the pure titanium clasps after 4500 loading cycles, in the titanium alloy clasp after 20,000 loading cycles, and in the gold alloy clasp after 21,000 loading cycles. The means differed significantly (p < 0.001). Activation of the clasp by bending it 0.5 mm increased the fatigue resistance of the cobalt-chromium alloy and gold alloy clasps but decreased the fatigue resistance of both pure titanium and titanium alloy clasps (p < 0.005). The results of this study suggest that significant differences exist in the fatigue resistance of removable denture clasps made from different commercial cast metals, which may cause loss of retention of the removable partial denture and clasp failures.