Abstract: Objective: To compare fatigue attenuation of high Co-Cr-Mo alloy and Co-Cr alloy clasps which were in the same deformation and cyclic number under different pH values. Methods: V and W were used to cast twenty straight clasps respectively which were divided into 4 groups and tested in the air and in the artificial saliva of pH equal to 4.0,6.7 and 8.0 separately.Then the load-deformation test was carried on specimens to get terminal load as a percentage of initial load with the universal testing machine for 0.8 mm deformation and condition of cyclic loading 20000 times. Surfaces were examined by SEM. Results: The attenuation of W group was higher than that of V group. The minimum ones was in the air. And specimen attenuation increased with increment of experimental pH value. The attenuation of V was the most in the pH=4 group. Conclusion: Using Vitallium 2000 plus casting clasps, the removable partial denture can keep the longer initial treatment effect.

Key words: Attenuation, Clasp, pH, Fatigue