title: The effect of core:dentin thickness ratio on the bi-axial flexure strength and fracture mode and origin of bilayered dental ceramic composites.
abstract: OBJECTIVE
  The aim of the current study was to assess the effect of core:dentin thickness ratio on the flexure strength, fracture mode and origin of bilayered dental ceramic composite disc specimens.
  
  
  METHODS
  Sets of 30 bilayered composite discs with core:dentin thickness ratio of 2:1, 1:1 and 1:2 were tested in bi-axial flexure with both the reinforcing core and veneering dentin loaded in tension. Mean flexure strengths, standard deviations and associated Weibull Moduli (m) were determined. A combination of optical and scanning electron microscopy was employed for identification of the fracture mode and origin.
  
  
  RESULTS
  The core:dentin ratio influenced the bi-axial flexure strength and reliability of the flexure strength data when both the reinforcing core and veneering dentin porcelain were tested in tension. The strength and reliability was increased for a core:dentin thickness of 2:1. The number of fracture fragments, the frequency of occurrence of specimen delaminations, Hertzian cone formations and sub-critical radial cracking in the bilayered dental ceramic composite disc shaped specimens was also dependent on the core/dentin ratio and the surface loaded in tension.
  
  
  CONCLUSIONS
  Core:dentin thickness ratio influences the bi-axial flexure strength and fracture mode and origin in bilayered dental ceramic composite specimens.
authors.affiliation: Biomaterials Unit, School of Dentistry, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, UK. g.j.fleming@bham.ac.uk
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
authors.forename: Sherin F A
authors.initials: SF
authors.lastname: El-Lakwah
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Harris
authors.forename: Peter M
authors.initials: PM
authors.lastname: Marquis
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D019245:Compressive Strength; D003776:Dental Porcelain / Q000737:chemistry*; D003801:Dental Veneers; D004548:Elasticity; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: C483027:vitadur alpha; D003776:Dental Porcelain