The effect of occlusal rest size and shape on yield strength.
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.
Sato
Yuuji
Y
Department of Geriatric Dentistry, School of Dentistry, Showa University, Tokyo, Japan. sato@senzoku.showa-u.ac.jp
Shindoi
Nobuaki
N
Koretake
Katsunori
K
Hosokawa
Ryuji
R
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