Surface contact fatigue and flexural fatigue of dental restorative materials

Antagonistic contact on a dental restoration may produce surface and subsurface stresses leading to fatigue wear as well as to bulk stressing, eventually causing catastrophic failure. It was the aim of the present work to study the outcome of two different approaches to fatigue testing of materials involving either surface contact fatigue or flexural fatigue mechanisms. A range of materials was tested, including conventional glass-ionomers, resin-modified glass-ionomers, poly-acid modified composites, and composites. Materials were prepared and tested using both surface contact and flexural fatigue. The results show that conventional glass-ionomers have the least resistance to fatigue under both regimes while composites have the longest fatigue lives and the highest values of flexural fatigue limit. However, the results also support the fact that catastrophic failure should be investigated separately from surface contact fatigue. Within the group of composite products tested, a hybrid composite material had a significantly greater flexural fatigue limit than a microfilled one, but the latter material had a significantly greater surface contact fatigue life, indicating that wear behavior cannot be predicted from bulk fracture characteristics and vice versa. The process of wear occurs by a combination of a number of fundamental processes, and the contribution fatigue makes will vary according to the environment and nature of the material.