title: Mathematical analysis of occlusal rest design for cast removable partial dentures.
abstract: OBJECTIVE
  To establish the minimum dimensions for a non-precious cast metal occlusal rest by using mathematical analysis. An occlusal rest in a removable partial denture (RPD) provides vertical support and allows occlusal forces to be transmitted through the long axis of the abutment tooth.
  
  
  METHODS
  The stress status of an occlusal rest in a posterior tooth-bounded RPD resembles that of a cantilever beam under a uniformly distributed load. A mathematical model based on a short rectangular cantilever beam was derived by using the yield strengths of a cast cobalt-chromium alloy and a cast titanium alloy (Ti-6Al-4V), with an applied static occlusal force of 400 N.
  
  
  RESULTS
  For the cobalt-chromium alloy, the minimum rectangular dimensions for a 2.0 mm long occlusal rest are; when the width is 2.0 mm, the depth or thickness should be at least 1.03 mm. For the titanium alloy, the minimum dimensions are; when the width is 2.0 mm, the depth or thickness should be at least 0.85 mm. A decrease in the occlusal width will increase the bending stress, requiring a thicker rest for compensation, which may lead to dentin exposure during the rest seat preparation.
  
  
  CONCLUSIONS
  The mathematical analysis found that the traditional spoon-shaped occlusal rest seat dimensions comply with the mechanical requirements for non-precious cast metal occlusal rests in RPDs.
authors: Faculty of Dentistry, Prince Philip Dental Hospital, Hong Kong, SAR, PR China.
authors: Nathan K C
authors: NK
authors: Luk
authors: Victor H F
authors: VH
authors: Wu
authors: Bernard M H
authors: BM
authors: Liang
authors: Ya-Ming
authors: YM
authors: Chen
authors: Kevin H K
authors: KH
authors: Yip
authors: Roger J
authors: RJ
authors: Smales
mesh_terms: D003766:Dental Occlusion; D003799:Dental Stress Analysis / Q000379:methods*; D003832:Denture, Partial, Removable; D008962:Models, Theoretical