Fracture toughness of dental amalgams

The fracture toughness of selected low and high copper content amalgams has been determined using three testing methods. A miniature single edge notched three point bend specimen, based on BS 5447, was found to give the most reliable values of fracture toughness, determined both as the work of fracture and as the opening mode plane strain critical stress intensity factor. The conventional low copper amalgam, Aristaloy, proved to be tougher under all test conditions than the high copper amalgams. It is suggested that time-dependent plastic flow mechanisms are responsible for this behaviour.