Fracture toughness and hardness evaluation of three pressable all-ceramic dental materials.
OBJECTIVE
This study evaluates the fracture toughness and hardness of three pressable all-ceramic materials: IPS-Empress, Empress 2 and an experimental ceramic material.


METHODS
Fifteen discs and 15 bars per material were prepared. Fracture toughness was measured with two different techniques: indentation fracture and indentation strength. During the indentation fracture tests the hardness of each material was also measured. Statistical significance among groups of population was studied using one-way Anova and Tukey's multiple comparison tests.


RESULTS
Fracture toughness results using the indentation strength technique (with three-point bending and biaxial flexure tests) were: IPS-Empress (1.39 (SD 0.3) and 1.32 (SD 0.3)); Empress 2 (3.14 (SD 0.5) and 2.50 (SD 0.3)) MPa x m(1/2); and the experimental ceramic (3.32 (SD 0.6) and 2.43 (SD 0.3)) MPa x m(1/2). The indentation fracture technique generated orthogonal cracks of different lengths for Empress 2 and the experimental ceramic, whether perpendicular or parallel to the lithium disilicate elongated crystals. Thus, two values were reported: Empress 2 (1.5 (SD 0.2) and 1.16 (SD 0.2)) MPa x am(1/2) and the experimental ceramic (1.67 (SD 0.3) and 1.15 (SD 0.15)) MPa x m(1/2). The IPS-Empress indentation fracture result was 1.26 (SD 0.1). The hardness results were: 6.6, 5.3 and 5.5 GPa for IPS-Empress, Empress 2 and the experimental ceramic, respectively.


CONCLUSIONS
No significant differences in fracture toughness and hardness results were found between Empress 2 and the experimental ceramic (P>0.05 ANOVA). Both materials exhibited fracture toughness anisotropy following pressing. They demonstrated improved fracture toughness and reduced hardness compared with IPS-Empress P<0.05(ANOVA), which should be beneficial for clinical applications.
Albakry
Mohammad
M
Biomaterials Science Research Unit, Faculty of Dentistry, The University of Sydney, Suite G11, National Innovation Centre, Australian Technology Park, Eveleigh, NSW 1430, Australia. albakrym@hotmail.com
Guazzato
Massimiliano
M
Swain
Michael Vincent
MV
D000704:Analysis of Variance; D018360:Crystallography, X-Ray; D003776:Dental Porcelain; D004548:Elasticity; D006244:Hardness; D006245:Hardness Tests; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D018709:Statistics, Nonparametric; D013718:Tensile Strength
D003776:Dental Porcelain