Investigations of subcritical crack propagation of the Empress 2 all-ceramic system

摘要

Introduction. The mechanical properties and slow crack propapagation of the all-porcelain system Empress~® 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress~® 2 and the veneering compounds "Empress~® 2 and Eris~® were examined. Methods. For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress~® 2 system, the fracture toughness K_(IC) was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. Results. The newly developed veneering ceramic Eris~® showed a higher fracture strength (σ_0 = 66.1 MPa) at a failure probability of P_F = 63.2%, and crack growth parameters (n = 12.9) compared to the veneering ceramic Empress~® 2 (σ_0 = 60.3 MPa). For Empress~® 2 veneer the crack propagation parameter n could only be estimated (n = 9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress~® 2 framework m = 4.6; Empress~® 2 veneer m = 7.9; Eris~® m = 6.9) were much lower than the minimum demanded by the literature (m = 15). Significance. The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.