Effects of cyclic loading on the strength of all-ceramic materials.
OBJECTIVE
To investigate the effects of fatigue on the strength of materials used in all-ceramic crowns, the biaxial flexural strength of all-ceramic restorative materials was measured with precracked and laminated specimens after cyclic loading.


METHODS
Two types of all-ceramic systems were used to prepare specimens: a glass-infiltrated alumina core system (In-Ceram) and a leucite-reinforced feldspathic porcelain system (IPS-Empress). Monolayer and laminated disks with a diameter of about 11.75 mm and a thickness of 1.20 +/- 0.05 mm were prepared. The biaxial flexural strength of the specimens that were polished and/or created with a precrack was measured. Their strength was also measured following cyclic loading. A cyclic load that was 60% of the mean breaking load of the specimens (before cyclic loading) was applied to specimens for 10(5) cycles in 37 degrees C water.


RESULTS
Although 20% to 30% of the polished specimen samples fractured during cyclic loading, the biaxial flexural strength of specimens that survived the cyclic loading was nearly the same as that of specimens not subjected to the cyclic loading. The strength of the alumina system decreased with the introduction of precracks, and nearly all specimens fractured during cyclic loading. The strength of the leucite system, however, did not decrease with the presence of precracks, and no fractures were observed on these specimens during cyclic loading.


CONCLUSIONS
These results suggest that although the alumina system has high flexural strength, it is more sensitive to flaws and susceptible to fatigue fracture. The effect of fatigue on the leucite system appears to be low.
Ohyama
T
T
Department of Dental Materials Science, Tokyo Dental College, Chiba, Japan. t-ohyama@kb3.so-net.ne.jp
Yoshinari
M
M
Oda
Y
Y
D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D000704:Analysis of Variance; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry*; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D013718:Tensile Strength; D016474:Weight-Bearing
D000538:Aluminum Silicates; C075815:IPS-Empress ceramic; D003776:Dental Porcelain; C078519:leucite; C070870:In-Ceram; D000537:Aluminum Oxide