RELATIONSHIP BETWEEN STATIC CHEMICAL AND CYCLIC MECHANICAL FATIGUE INA FELDSPATHIC PORCELAIN

Objectives. The goal of this study was to determine if static chemical and cyclic mechanical fatigue are independent, or if they interact to produce greater than additive strength loss in a feldspathic porcelai n. Methods. A blunt indentation technique was used to investigate the response of a feldspathic dental porcelain to cyclic mechanical fatigu e and static chemical fatigue. All specimens were fabricated in a dry inert environment and then mechanically fatigued by cyclic loading and strength-tested in dry inert nitrogenous, ambient or wet environments . A series of experiments were performed to evaluate the effects of ch emical and mechanical fatigue, and their interaction on strength loss; to determine the effects of, and interaction between, the factors of cyclic fatigue environment and strength test environment on strength; to ascertain if the type of environment during strength testing influe nced specimen strength; and to distinguish between chemical damage cau sed by exposure to moisture alone and stress corrosion damage resultin g from the strength testing environment, using a pair of two-way analy sis of variance, a single one-way analysis of variance and a t-test (p < 0.05). Results. These experiments indicated that both static chemic al fatigue and cyclic mechanical fatigue significantly reduced specime n strength, but they did not interact to produce greater than summativ e effects. It was also learned that chemical fatigue was not detected on initial exposure to moisture and that it occurred to a small extent during mechanical fatigue cycling, and primarily occurred during stre ngth testing through a stress-corrosion phenomenon. Micrographs visual ly evaluated the effects of mechanical and chemical fatigue on surface contact damage. Significance. As both static chemical and cyclic mech anical fatigue influenced porcelain strength, they should both be cons idered in future evaluations. However, because they largely acted inde pendently, they can be studied separately.