Compressive Properties of Enamel , Dental Cements , and Gold

The compressive properties of human enamel and dentin have been reported by Stanford, Paffenbarger, Kumpula, and Sweeney.' The elastic modulus of occlusal, side, and cusp enamel was reported to be 1.8, 6.0, and 8.2 X 106 psi, respectively. The corresponding values for the proportional limit were 16,800, 21,000, and 34,200 psi and, for the compressive strength, 19,400, 28,300, and 40,200 psi. An improved procedure for preparing compressive specimens of hard tooth tissues and some restorative materials was published by Stanford, Weigel, Paffenbarger, and Sweeney.2 The compressive properties of enamel were within the experimental error of the earlier values, and additional values relating compressive properties to environment of development and orientation were reported. In addition, the compressive properties of plastics, amalgam, silicate cement, zinc phosphate cements, and dental golds were listed. Tyldesley3 determined the mechanical properties of enamel by using a transverse type of loading system. The elastic modulus of enamel was reported to be 19 X 106 psi in bending. The proportional limit and compressive strength were found to coincide at an average value of 11,000 psi. The published values for the compressive strength of enamel appear low when compared with the values listed for human dentin. Craig and Peyton4 reported an average compressive strength for dentin of 43,100 psi; Stanford et al.1 gave a value of 50,400 psi; and Tyldesley3 published a value of 38,800 for the breaking stress. The highest average compressive-strength value of 40,200 psi reported for cusp enamel is, in general, lower than those reported for dentin.' 2 These results do not appear reasonable when the hardness and general working characteristics of enamel and dentin are compared. The principal purpose of this investigation, therefore, was to re-evaluate the compressive properties of proportional limit, compressive strength, and elastic modulus of human enamel, using improved procedures for sample preparation. In addition, the dental literature included little information concerning the compressive properties of restorative materials measured on specimens approaching the size normally used in dentistry.2 Investigations of the effect of sample size on the compressive properties of amalgam indicated that higher values were obtained with smaller specimens. The second object of this study, therefore, was to determine the compres-