Fatigue behavior of resin composites in aqueous environments

Objectives. Interaction between mechanical and chemical fatigue of resin composites was investigated. Methods. Fatigue fracture resistance of composites after (1) water immersion and under (2) dry and (3) aqueous conditions was analyzed using a fatigue crack propagation test. The characteristics of fatigue crack propagation were expressed as the correlation between the fatigue crack growth rate (da/dN) and stress intensity factor range (AK) and by the fatigue crack growth threshold (Delta Kth). Following the fatigue test, a fractographic examination was performed by scanning electron microscopy. Results. Contrary to common perception, fatigue crack propagation was retarded under aqueous conditions but accelerated after water immersion. In addition, fatigue cracks detoured around inorganic macro-fillers, but penetrated organic fillers. Significance. It was concluded that the inverse effects of water on fatigue resistance of composites are dependent on the experimental conditions. Moreover, inorganic macro-fillers were shown to be functional in retarding fatigue cracks in composites. (C) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.