title: Dynamic retentive force of a mandibular unilateral removable partial denture framework with a back-action clasp.
abstract: OBJECTIVE
  The purpose of this study was to investigate the dynamic retentive force of a mandibular unilateral distal-extension partial denture framework with a back-action clasp that was designed in a buccally tilted cast on a dental surveyor. The retention mechanism of this framework was analyzed in comparison with other typical unilateral and bilateral frameworks for the mandibular Kennedy class II case.
  
  
  METHODS
  Experimental gold alloy frameworks of three designs were repositioned to the master cast, and lifted upward to the vertical direction to the occlusal plane. The load required to dislodge each framework was recorded. The retentive force of each framework was determined by the maximum load in a dislodgment cycle. The bending strength of a plain clasp pattern of the same length as the clasp arm used in each framework was also measured by cantilever beam test.
  
  
  RESULTS
  The mean retentive force of the unilateral framework with a back-action clasp of relatively low bending strength was significantly higher (P < 0.01) than that of the unilateral framework with two Akers clasps of relatively high bending strength, and 70 to 80% of the bilateral framework with two Akers clasps on the edentulous side and a double Akers clasp on the contralateral side. The unilateral framework with a back-action clasp showed the greatest early load resistance in the dislodgment cycle among the three designs.
  
  
  CONCLUSIONS
  The reasonable retention mechanism was demonstrated by the unilateral framework with a back-action clasp.
authors.affiliation: Department of Masticatory Function Rehabilitation, Graduate School, Tokyo Medical and Dental University, Japan. park.rpro@tmd.ac.jp
authors.forename: I
authors.initials: I
authors.lastname: Park
authors.forename: M
authors.initials: M
authors.lastname: Eto
authors.forename: N
authors.initials: N
authors.lastname: Wakabayashi
authors.forename: M
authors.initials: M
authors.lastname: Hideshima
authors.forename: T
authors.initials: T
authors.lastname: Ohyama
mesh_terms: D000044:Dental Abutments; D016734:Dental Clasps; D019232:Dental Restoration Failure; D003779:Denture Design; D003781:Denture Retention; D003832:Denture, Partial, Removable; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000145:classification / Q000534:rehabilitation; D008334:Mandible; D008422:Materials Testing; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D016474:Weight-Bearing
chemical_list: D006047:Gold Alloys