Fatigue resistance and stress of wrought-steel wire clasps.

PURPOSE

The objective of this study was to determine the fatigue resistance of wrought-steel wire clasps used for removable partial dentures.

MATERIALS AND METHODS

Five wrought-steel wires with cross-sectional diameters of 1.2, 1.1, 1.0, 0.9, and 0.8 mm were tested using a deflection fatigue test with deflections of 0.4 to 0.7 mm. The force and stress required to cause deflection was determined, as well as the number of loading cycles required to cause fatigue fracture. The fracture surfaces of the wrought-steel wire clasps were examined with a scanning electron microscope.

RESULTS

The number of loading cycles required to cause fatigue fracture increased with reduced deflection of the wrought wire (p < .005). To obtain fatigue resistance for loading cycles of over 10(6), the stress in the wrought-steel wire clasp should remain under 1.0 GPa.

CONCLUSIONS

These results suggest that to avoid fractures of wrought-steel wire clasps caused by bending fatigue, the stress on the clasp during its deflection should be taken into account.