Fatigue of dental ceramics in a simulated oral environment

Fatigue in ceramics refers to the subcritical growth of cracks, aided by the combined influence of water and stress. The dynamic fatigue (constant stressing rate) method was used to obtain subcritical crack growth parameters for three dental ceramics: a feldspathic porcelain, an aluminous porcelain, and a fine-grain, polycrystalline core material. The constant stressing rate experiments were carried out at 37 degrees C for all three ceramics in distilled water, and, for the feldspathic porcelain, in artificial saliva as well. Considerable differences were found in the value of the crack growth exponent (n) among the three ceramics. The feldspathic porcelain was lowest in n-value, while the fine-grain ceramic had the highest n-value. No differences were found for the feldspathic porcelain with respect to n measured in water and in the artificial saliva. Lifetime prediction curves in 37 degrees C water, constructed from the n-values and inert strengths, showed that fatigue failure within five years is a good possibility for feldspathic porcelain specimens at stress levels which can reasonably be anticipated to occur in the oral environment. Little likelihood of failure was perceived for the fine-grain ceramic. The aluminous porcelain was intermediate between these two materials with respect to failure probability.