title: Investigations of subcritical crack propagation of the Empress 2 all-ceramic system.
abstract: BACKGROUND
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Clinic for Prosthetic Dentistry and Dental Materials Science, University of Saarland, Kierbergerstrasse 1, 66421 Homburg/Saar, Germany. zmgimi@uniklinik-saarland.de
authors.forename: Gergo
authors.initials: G
authors.lastname: Mitov
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
authors.forename: Mohammad Abed
authors.initials: MA
authors.lastname: Rabbo
authors.forename: Anselm
authors.initials: A
authors.lastname: Petschelt
authors.forename: Peter
authors.initials: P
authors.lastname: Pospiech
mesh_terms: D000465:Algorithms; D002516:Ceramics / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003801:Dental Veneers; D004548:Elasticity; D006244:Hardness; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry*; D008422:Materials Testing; D018583:Pliability; D011336:Probability; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
chemical_list: C118557:Empress 2; C500744:Eris ceramic; D018020:Lithium Compounds; D003776:Dental Porcelain