Effect of friction coefficient on Akers clasp retention.

STATEMENT OF PROBLEM

Retentive force control of clasp retainers is one of the most essential factors for the successful function of removable partial dentures. However, it is not yet known how the friction coefficients differ among restored abutments and clasp materials, and how the friction coefficients affect the retention of clasps.

PURPOSE

The purposes of this study were to clarify the friction coefficients among restored abutments and clasp materials and to estimate the effect of friction coefficients on the retention of clasps.

MATERIAL AND METHODS

The coefficients of static friction between three clasp materials (type IV gold, high Pd, and cobalt-chromium [Co-Cr] alloys) of two surface treatments (polished and sandblasted) and four abutment materials (human enamel, porcelain, type IV gold, and high Pd alloys) were evaluated under three conditions (dry, wet with water, and wet with saliva), and theoretically, the effect of the friction coefficients on clasp retention was estimated.

RESULTS

The friction coefficients under various conditions ranged from 0.08 (polished Co-Cr clasp on type IV abutment in dry condition) to 0.37 (sandblasted Co-Cr clasp on high Pd abutment in dry condition). The theoretical estimation clarified that the retentive force of the clasp was linear to the friction coefficient.

CONCLUSION

The retentive force increased linearly with increasing friction coefficient between abutment material and clasp material according to the newly developed formula. This study suggested that clasp designs should be changed depending on abutment materials.