Dynamic mechanical properties of amalgams

A recently developed dynamic mechanical analysis technique was utilized to determine the setting rates of dental amalgams. Via a compound parallel beam apparatus the dynamic mechanical properties of five amalgam materials were continuously measured at 37 degrees C within ca. 7 min after the start of trituration. Over a 15 hr period results showed that the modulus of elasticity (Ea) increased from 1.2 X 10(10) Pa to 6.5 X 10(10) Pa--the latter generally approaching those values reported via ultrasonic techniques. Moduli results via compression tests on microspecimens (3 X 2 X 1 mm) paralleled previous reliable literature data, nominally yielding values for Ea of 2-3 X 10(10) Pa. The extent of Ea scatter from both inter- and intrapreparer experiments appeared similar, although superior technique generally could be recognized by a systematic shift of the mean results to higher Ea's. In addition to modulus studies both compressive strengths (sigma max) and their corresponding strains (epsilon) were measured on microspecimens at a strain rate (epsilon) of 0.031 min-1, with a significant increase being noted in sigma max for the one material tested at over an order of magnitude increase in epsilon.