Measurement of strain rate behaviour in complete mandibular dentures

A major cause of fracture in complete lower dentures is due to the denture falling onto a hard floor. Impact failure has never been investigated in complete dentures and in a material which is strain rate dependent, a knowledge of the maximum strain and strain rate at failure is essential if laboratory tests are to evaluate materials in a realistic manner. The work described includes brittle lacquer studies to establish the strain pattern which occurs when a denture is dropped from a height of 1 metre. This was used to orientate strain gauges and experimental dentures were then hit by a specially constructed ram driven at known velocities by a spring, whilst the strain was recorded on a storage oscilloscope. Photographs of the stored wave form were then used to establish the results at ram velocities equal to that of a denture falling 1 metre. Maximum strains were achieved of 11 x 10(3) microstrain and strain rates of 1.04 x 10(3) microstrain/ms. Laboratory impact machines for testing denture materials should therefore be designed to achieve these figures.