title: Effect of friction coefficient on Akers clasp retention.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Removable Prosthodontics, Hiroshima University School of Dentistry, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Sato
authors.forename: Y
authors.initials: Y
authors.lastname: Abe
authors.forename: Y
authors.initials: Y
authors.lastname: Yuasa
authors.forename: Y
authors.initials: Y
authors.lastname: Akagawa
mesh_terms: D000704:Analysis of Variance; D002858:Chromium Alloys / Q000737:chemistry; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D016734:Dental Clasps; D003743:Dental Enamel / Q000502:physiology; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D003779:Denture Design; D003781:Denture Retention; D003832:Denture, Partial, Removable; D017276:Friction; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D016014:Linear Models; D010165:Palladium / Q000737:chemistry; D012463:Saliva / Q000502:physiology; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water
chemical_list: D002858:Chromium Alloys; D003722:Dental Alloys; D003764:Dental Materials; D006047:Gold Alloys; D014867:Water; D010165:Palladium