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

BACKGROUND

Fatigue of denture clasp alloys causes clasp failures and decreases the retention of removable partial dentures. Little information is available on how the environment (dry, water, artificial saliva) effects the fatigue behavior of cast cobalt-chromium alloy clasps.

OBJECTIVE

This study determined the effect of water and the artificial saliva on the resistance of cast cobalt-chromium alloy to the deflection fatigue.

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 resistance to fatigue. To establish whether there were indications of alloy corrosion occurring during the fatigue test, the testing liquid was analyzed retrospectively with an atomic absorbance spectroscopy. To determine elemental composition of the fracture surface, fracture surfaces of the test bars were analyzed with a scanning electron microscope and energy dispersive spectroscopy.

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 testing water and in artificial saliva. Energy dispersive spectroscopy analysis revealed differences in elemental composition of a fatigue fracture surface compared with that of a 1-bend fracture.

CONCLUSIONS

The results suggest that both water and artificial saliva reduce the fatigue strength of cobalt-chromium alloy, explained by corrosion of the alloy in the wet environment.