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°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 × 1010 Pa to 6.5 × 1010 Pa—the latter generally approaching those values reported via ultrasonic techniques. Moduli results via compression tests on microspecimens (3 × 2 × 1 mm) paralleled previous reliable literature data, nominally yielding values for Ea of 2–3 × 1010 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 (σmax) and their corresponding strains (ϵ) were measured on microspecimens at a strain rate (ϵ) of 0.031 min−1, with a significant increase being noted in σmax for the one material tested at over an order of magnitude increase in ϵ.