Flexural strength and fracture toughness of dental core ceramics

Statement of problem. Many different strengthened all -ceramic core materials are available. In vitro study of their mechanical properties, such as flexural strength and fracture toughness, is necessary before they are used clinically. Purpose. The purpose of this study was to evaluate and compare the mechanical properties of 6 commonly used all-ceramic core materials using blaxial flexural strength and indentation fracture toughness tests. Material and methods. Specimens of 6 ceramic core materials (Finesse, Cergo, IPS Empress, In-Ceram Alumina, In-Ceram Zirconia, and Cercon Zirconia) were fabricated (n=25) with a diameter of 15 mm and width of 1.2 +/- 0.2 mm. For each group, the specimens were tested to compare their blaxial flexural strength (piston on 3 balls) (n=15), Weibull modulus, and indentation fracture toughness (n=10) (IF method). The data were analyzed with 1-way ANOVA test (alpha=.05). The Tamhane multiple comparison test was used for post hoc analysis. Results. Mean (SD) of blaxial flexural strength values (MPa) and Weibull modulus (m) results were: Finesse (F): 88.04 (31.61), m=3.17; Cergo (C): 94.97 (13.62), m=7.94; IPS Empress (E): 101.18 (13.49), m=10.13; In-Ceram Alumina (ICA): 341.80 (61.13), m=6.96; In-Ceram Zirconia (ICZ): 541.80 (61.10), m=10.17; and Cercon Zirconia (CZ): 1140.89 (121.33), m=13.26. The indentation fracture toughness results showed that there were significant differences between the tested ceramics. The highest fracture toughness values (MPa x m(0.5)) were obtained with the zirconia-based ceramic core materials. Conclusions. Significant differences were found in strength and toughness values of the materials evaluated. Cercon Zirconia core material showed high values of blaxial flexural strength and indentation fracture toughness when compared to the other ceramics studied.