Effect of water and artificial saliva on the low cycle fatigue resistance of cobalt-chromium dental alloy

Statement of problem. Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little informat ion is available on how the environment (dry, water, artificial saliva) eff ects the fatigue behavior of cast cobalt-chromium alloy clasps. Purpose. This study determined the effect of water and the artificial saliv a on the resistance of cast cobalt-chromium alloy to the deflection fatigue . Material and methods. Test bars (n = 10) were tested either dry, in water, or in artificial saliva (Fusayama type) with a constant deflection fatigue test. The number of loading cycles before fracture was registered as resist ance to fatigue. To establish whether there were indications of alloy corro sion occurring during the fatigue test, the testing liquid was analyzed ret rospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars we re analyzed with a scanning electron microscope and energy dispersive spect roscopy. Results. The bars that were tested dry had a mean fatigue resistance of 78, 000 loading cycles, whereas test specimens tested in artificial saliva had a resistance of 59,000 loading cycles and 36,000 for those tested in water. Atomic absorbance spectroscopy revealed small amounts of cobalt (Co) in te sting water and in artificial saliva. Energy dispersive spectroscopy analys is revealed differences in elemental composition of a fatigue fracture surf ace compared with that of a 1-bend fracture. Conclusions. The results suggest that both water and artificial saliva redu ce the fatigue strength of cobalt chromium alloy, explained by corrosion of the alloy in the wet environment.