The effects of cyclic stress on dental polymethylmethacrylate. II. Flexural fatigue.

Mechanisms of fatigue failure in polymers and the aims of fatigue testing have been examined, and factors affecting testing summarized. In the light of available work in several fields, parameters have been suggested for realistic flexural fatigue testing of denture base resins. A testing machine has been developed, with which the changes in properties of acrylic resin after fatigue in different environments can be studied. These changes developed gradually after 10(4) cycles and were related to the development of bulk crazing rather than to thermal effects. The amount of decay in the elastic modulus was not such that the material could have been said to have "failed".