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

Dent Mater. 2008 Feb;24(2):267-73. doi: 10.1016/j.dental.2007.05.010. Epub 2007 Jul 12.

Abstract

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 (sigma(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 (sigma(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.

Publication types

  • Comparative Study

MeSH terms

  • Algorithms
  • Ceramics / chemistry
  • Dental Porcelain / chemistry*
  • Dental Restoration Failure
  • Dental Veneers
  • Elasticity
  • Hardness
  • Humans
  • Lithium Compounds / chemistry*
  • Materials Testing
  • Pliability
  • Probability
  • Stress, Mechanical
  • Surface Properties
  • Time Factors

Substances

  • Empress 2
  • Eris ceramic
  • Lithium Compounds
  • Dental Porcelain