Yoshitaka Yuasa

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.

Finite Element Analysis on Dimension of I-bar Clasps of Removable Partial Denture Patients.

To establish science-based I -bar clasp design of removable partial denture (RPD), the dimension of I -bar clasps of RPD patients was measured, and the stiffness and stress distribution of these I -bar clasps were evaluated with the finite element method. The results were as follows 1. The thicknesses and widths in cross-sections of I -bar clasps were 0.3•`1.0. 2. The width of the taper of horizontal arms of I -bar clasps was the largest (0.09). 3. The stiffness of I -bar clasps was greater than that of mechanical ideal I -bar clasps. 4. The stress analysis suggests a possibility of fatigue fracture or permanent deformation of I -bar