Evaluation of the static frictional coefficients of Co-Cr and gold alloys for cone crown telescope denture retainer applications.

The static frictional coefficients (SFC) of a Co-Cr and a gold alloys were evaluated for the application of a cone crown telescope system in removable prosthesis. The SFCs of the Co-Cr alloy were lower than those of the gold alloy. The SFC of the gold alloy decreased by annealing at 85°C in air and was restored by re-polishing, although that of the Co-Cr alloy was stable irrespective of the annealing. The XPS analysis revealed the formation of a surface oxide layer on the gold alloy after annealing. The decrease in the SFC of the gold alloy may have been caused by the formation of an oxide layer on the surface due to annealing. The relationships among such factors as the retentive force, SFC and cone crown angle indicate that the angle of the Co-Cr alloy should be lower than that of the gold alloy based on the Körber's model.