Strength, reliability, and mode of fracture of bilayered porcelain/core ceramics.
OBJECTIVE
The aim of this investigation was to compare the biaxial flexural strength, its reliability, and the mode of fracture of bilayered disks made of two core materials (In-Ceram Alumina and In-Ceram Zirconia), both veneered with conventional feldspathic porcelain (Vita Alpha).


METHODS
One hundred forty specimens (monolithic and bilayered) of In-Ceram Alumina, In-Ceram Zirconia, and Vita Alpha were made and tested with the biaxial flexural test. Finite element analysis was used to estimate the maximum tensile stress at fracture. Data were analyzed with one-way ANOVA, Tukey HSD, and Weibull distribution. SEM was used to identify the initial crack and characterize the fracture mode.


RESULTS
All specimens with the core material on the bottom surface were statistically significantly stronger and more reliable than those with the porcelain on the bottom surface. Among them, In-Ceram Zirconia was stronger than In-Ceram Alumina. There was no statistically significant difference among groups when the porcelain underwent tension. Two different modes of fracture were observed in the bilayered samples according to which material was on the bottom surface.


CONCLUSIONS
The material that underwent tensile stress dictated the strength, reliability, and fracture mode of the specimens. The design of the restorations and the actual distribution of the tensile stresses must be taken into account; otherwise, the significant contribution of stronger and tougher core materials to the performance of all-ceramic restorations may be offset by the weaker veneering porcelain.
Guazzato
Massimiliano
M
Biomaterials Science Research Unit, United Dental Hospital, Faculty of Dentistry, University of Sydney, Surry Hills, New South Wales, Australia. mgua2483@mail.usyd.edu.au
Proos
Kaarel
K
Sara
Georges
G
Swain
Michael Vincent
MV
D000704:Analysis of Variance; D003442:Crowns; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D004548:Elasticity; D020342:Finite Element Analysis; D008422:Materials Testing; D016876:Metal Ceramic Alloys; D018583:Pliability; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D013718:Tensile Strength; D015040:Zirconium
C483026:In-Ceram Alumina; C485633:In-Ceram Zirconia; D016876:Metal Ceramic Alloys; C472245:Vita Alpha; D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide