title: The effect of occlusal rest size and shape on yield strength.
abstract: BACKGROUND
  Occlusal rests, essential for conventional removable partial dentures, may fracture and cause failure of the prosthesis. It is unknown whether alterations in the size or shape of occlusal rests might improve their performance.
  
  
  OBJECTIVE
  In this in vitro study, 3-dimensional finite element analysis was used to evaluate the effects of occlusal rest size and shape on yield strength.
  
  
  METHODS
  An occlusal rest and a minor connector as part of a clasp assembly were modeled for 3-dimensional finite element analysis with 3 variations of width (2.0, 3.0, and 4.0 mm), thickness (0.7, 1.0, and 1.5 mm) and length (2.0, 3.0, and 4.0 mm). A concentrated vertical load of 100 N was applied at the most protruded point of the occlusal rest base. Maximal principal stress and yield strength were calculated. In addition, the following parameters were altered: radius of curvature at the inner connection (r), thickness of the minor connector (m), inclination of horizontal axis of occlusal rest (i), and thickness at the most protruded point (t).
  
  
  RESULTS
  Yield strength increased with increased width (183% to 242% from 2.0 to 4.0 mm) and thickness (141% to 230% from 0.7 to 1.5 mm). Alterations in length had a lesser effect on yield strength (120% to 178% from 4.0 to 2.0 mm). All other parameters except thickness at the most protruded point (t) affected yield strength.
  
  
  CONCLUSIONS
  The results of this in vitro study suggest basic principles for optimizing the size and shape of occlusal rests. In general, increased width and thickness are desirable, whereas overrounded or sharp line angles and excessive rest inclination should be avoided. These principles may be useful in removable partial denture design.
authors.affiliation: Department of Geriatric Dentistry, School of Dentistry, Showa University, Tokyo, Japan. sato@senzoku.showa-u.ac.jp
authors.forename: Yuuji
authors.initials: Y
authors.lastname: Sato
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Shindoi
authors.forename: Katsunori
authors.initials: K
authors.lastname: Koretake
authors.forename: Ryuji
authors.initials: R
authors.lastname: Hosokawa
mesh_terms: D003198:Computer Simulation; D016734:Dental Clasps; D003779:Denture Design; D003832:Denture, Partial, Removable; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D008954:Models, Biological; D013314:Stress, Mechanical; D013499:Surface Properties; D016474:Weight-Bearing