Finite element stress analysis of a restored axisymmetric first molar.

First molars with full gold crown preparations and a shoulder geometry were ideaIized by an axisymmetric model and analyzed by the photoelastic. as uell as the finite element method. The photoelastic model was constructed in two pieces, the restoration and the tooth with the preparation. The two pieces were then luted together and the model was loaded axisymmetrically with 100 lb; it was stress frozen, sliced, and analyzed with the help of a polariscope. The finite element model was subdivided into 348 elements. The radial and axial stresses were plotted as a function of the radius along various horizontal planes in the model. The maximum shear stresses calculated by the finite element method ivere compared to those obtained by the photoelastic method, and they were found to compare favorably. EXPERIMENTAL stress analysis of dental structures has been a topic of interest over the past quarter century. The object of such research was the determination and improvement of the mechanical strength of these structures. The photoelastic method, a well recognized engineering technique of stress analysis, first appeared in dental research with the publication by Noonan (1949). Noonan’s models were made of Bakelite, with the cavities packed with silver amalgam. A 55 lb load was applied to the center of the restoration. He found that: (a) a flat floor exhibited less stress concentration than the rounded one, and (b) retention points should not be sharp, but rounded to decrease stress concentration. (1955) presented a three-dimensional photoelastic study of an anterior jacket crown. Four models were analyzed and they concluded that the thicker the walls of the jacket, the greater its strength. They also found that maximum mesiodistal width of the preparation was important. Mahler and Peyton (1955) reviewed the general applications of photoelasticity as a research technique for analyzing stresses in dental structures. Haskins. Haack and Ireland (1954) studied the effects of rounding axio-pulpal line angles, as well as the stress distribution associated with the variations of vertical axial walls. They noticed that there was a marked reduction of stress when the pulpal wall was rounded and sloped. Walton and Leven Mahler (1956) published his findings of a disto-occlusal restoration ina primary mandibular first molar. He found that the stresses in the restoration in the region of the isthmus were tensile in nature. He also found that the sloping pulpal floor and the beveled pulpal floor exhibited less adverse stress than the flat pulpal floor. A study of strain patterns in jacket crowns on anterior teeth was published by Lehman and Hampson ( 1962) in England. They pointed out the effects of leaving rough surfaces on the prepared tooth and the ‘Receiced 11 September 1972. +Research Associate, Department of Dental Materials, School of Dentistry. SProfessor and Chairman. Department of Dental Materials, School of Dentistry. BAssociate Professor. krospace Engineering Department, School of Engineering.