Fracture toughness of heat-pressed andlayered ceramics
Richard Ansong, DDS, MSD,a Brian Flinn, MS, PhD,b
Kwok-Hung Chung, DDS, PhD,c Lloyd Mancl, PhD,d Motoaki
Ishibe, DDS, MSD,e and Ariel J. Raigrodski, DMD, MSf
Columbia University College of Dental Medicine, New York, NY;
University of Washington School of Engineering, Seattle, Wash;
University of Washington School of Dentistry, Seattle, Wash
Statement of problem. Veneering ceramic materials designed to be used with high noble alloy and zirconia-based
restorations have been reported to be susceptible to chipping in vivo.
Purpose. The purpose of this study was to evaluate and compare the fracture toughness of heat-pressed and layered
ceramics intended for zirconia and high-noble alloy substrates.
Material and methods. Bar specimens were fabricated from 8 different ceramics (Ivoclar-Vivadent [I] and Noritake[N]) intended for pressing (P) and layering (L) to high noble alloy (M) and zirconia (Z) substrates, following theISO 6872 protocol. The single edge notch beam test method was used to create a notch in the center of each specimen, which was then tested with a universal testing machine (n=6, cross-head speed=0.5 mm/min) and the fracture
force values recorded. These values were used to calculate the fracture toughness (K1c) for each specimen. Fracturesurfaces were examined with a scanning electron microscope, and the basic components of the tested ceramics weredetermined by using energy dispersive x-ray (EDX) spectroscopy. Data were analyzed with 3-way ANOVA, followed bymultiple comparisons using the Holm method (α=.05).
Results. The mean (SD) of the calculated fracture toughness values obtained ranged from 1.20 (0.04) MPa·m1/2(group NZL) to 1.74 (0.04) MPa·m1/2 (group IZL). Fracture toughness was significantly higher in group IZL (1.74) thangroup IZP (1.41), but lower in group NZL (1.20) than group NZP (1.36) (P<.001). Fracture toughness was somewhat
lower in group IML (1.36) than group IMP (1.47) (P=.018), and no significant difference was found between group
NML and group NMP (P=.14). Veneering ceramics used with a metal substrate showed a crystalline structure mixed
with a glassy phase pattern on the fracture surface. The results of EDX analysis on the fracture surfaces indicated thatthe tested ceramics were composed of Si, Al, K, Na, Mg, and oxygen elements.
Conclusions. Ceramics used for veneering zirconia substrate may have various fracture toughness values that relate
primarily to the processing technique. (J Prosthet Dent 2013;109:234-240)

Clinical Implications

Results of this study suggest that, in general, and assuming all otherphysical characteristics remain virtually the same, it is desirable touse a ceramic veneering material with a higher K1C.
Associate Clinical Professor, Department of Restorative Dentistry, Columbia University, College of Dental Medicine.
Research Associate Professor, Materials Science & Engineering, University of Washington School of Engineering.
cProfessor, Department of Restorative Dentistry, University of Washington School of Dentistry.
dResearch Associate Professor, Oral Health Sciences, University of Washington School of Dentistry.
eAffiliate Assistant Professor, Graduate Prosthodontics, Department of Restorative Dentistry, University of Washington School ofDentistry.
fProfessor and Director, Graduate Prosthodontics, Department of Restorative Dentistry, University of Washington School ofDentistry.
abThe Journal of Prosthetic Dentistry

Ansong et al