Experimental stress analysis of dental restorations. Part IX. Two-dimensional photoelastic stress analysis of porcelain bonded to gold crowns

Abstract

A two-dimensional photoelastic model study of porcelain fused to gold restorations was conducted on models that were 20 times normal size, using three plastics having a ratio of the elastic moduli similar to those of the actual materials. Isochromatic and isoclinic patterns were obtained and the principal stresses were separated in critical regions. The study resulted in the following generalizations based on the models used. (1) In a crown restoration the cement functions as a stress distributor. (2) A restricted occlusal surface provides a more favorable stress distribution. (3) A shoulder type preparation with rounded angles seems to be the best geometry for the porcelain bonded to gold crown restorations. (4) The gold part of the crown acts as a stress distributor and absorbs most of the stress put on the crown. (5) Sharp grooves should be avoided in carving the occlusal surface of the porcelain.