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[A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact].

OBJECTIVE
To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue.


METHODS
Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant.


RESULTS
Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens.


CONCLUSIONS
Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.