Effects of aging and cyclic loading on the mechanical properties of glass ionomer cements.

The purpose of this study was to examine the effect of cyclic loading on the flexural strength and fracture toughness of a conventional glass ionomer cement (GIC), a metal containing GIC, hybrid GICs, and, for comparison, a composite. Two sets of specimens were evaluated: a set of controls (at 37 degrees C and 95% humidity) and a set aged for 9 months at 37 degrees C in water. The specimens were tested in static loading in air and water, and cyclic loaded in water. Cyclic loading and aging decreased the flexure strength of all materials significantly. However, wet static fracture toughness did not change on aging, and occasionally increased. Cyclic fracture toughness was lower with all materials except a hybrid glass ionomer without aging. Deterioration in properties was related to relative amount of glass ionomer vs. the resin component. Both flexural strength and fracture toughness of these materials were significantly affected by testing environment, aging and cyclic loading. The lower the resin component of the material, the lower the mechanical properties. The influence of these parameters should be given importance in considering their clinically durability in the oral environment.