Creep of dental amalgam.

The steady-state creep rates of dental amalgams were measured and the creep rates were correlated with the microstructure of the amalgams. The influence of manipulation variables on creep rate and microstructure are evaluated. The samples were either mechanically or hand triturated, hand condensed, and stored at 20 degrees C for 7 d. The specimens were subjected to a constant tensile load for 24 h, and the elongation was measured with a displacement transducer. The smallest creep rate was found on a spherical amalgam, and the highest on an amalgam made from a preamalgamated fine grain alloy. A correlation between microstructure and creep rate could be demonstrated. The amount of gamma2 phase did not seem to influence the creep rate. Amalgams that had large closely packed gamma particles surrounded by a small volume fraction of gamma1 phase exhibited a low creep rate. Amalgams that had small broken up gamma particles surrounded by a large volume fraction of gamma1 exhibited a high creep rate. Abusive manipulation of lathe-cut amalgam alloys resulted in high creep rates, small broken up gamma particles and a high volume fraction of gamma1.