The evaluation of post‐retained crowns using a custom designed fatigue machine

Abstract

There are many published reports of static tests on dental materials that are required to perform clinically under a range of load amplitudes and cyclic frequencies. There are fewer reports in the dental literature of fatigue tests on dental structures and materials, and these are reviewed in this paper along with a description of the design, manufacture and commissioning of a machine which can apply chosen cyclic load/time characteristics up to a maximum amplitude of 700 N and frequency of 5 Hz. The machine design is not specific to particular test specimens but is widely applicable within dental materials testing. The machine is being used for a continuing study of post-retained crowns, cemented with glass-ionomer cement. The planning of fatigue tests and the interpretation of results is discussed with reference to the experience of previous authors, and it is concluded that a survival analysis approach offers a means of understanding materials' performances. The initial results from a random, blocked comparison of three glass-ionomer luting cements indicated that cyclic loads can be identified to give a 50% survival probability for specimens. It is expected that loads experienced in vivo have lower amplitude than those applied in this study, however, such loading cycles have been chosen to facilitate material comparisons. It is concluded that gaining significant results under laboratory fatigue conditions is difficult, but that they may usefully complement clinical trials.