title: [Effect of core: dentin thickness ratio on the flexure strength of IPS Empress II heat-pressed all-ceramic restorative material].
abstract: OBJECTIVE
  To evaluate the effect of core:dentin thickness ratio on the flexure strength, fracture mode and origin of bilayered IPS Empress II ceramic composite specimens.
  
  
  METHODS
  IPS Empress II core ceramic, dentin porcelain and bilayered composite specimens with core:dentin thickness ratio of 2:1 and 1:1 were tested in three-point flexure strength. Mean strengths and standard deviations were determined. The optical microscopy was employed for identification of the fracture mode and origin.
  
  
  RESULTS
  The flexure strength of dentin porcelain was the smallest(62.7 MPa), and the strength of bilayered composite specimens was smaller than single-layered core ceramic(190.2 MPa). The core: dentin ratio did not influence the strength of bilayered composite specimens. The frequency of occurrence of bilayered specimen delaminations was higher in the group of core: dentin thickness ratio of 1:1 than in the group of 2:1.
  
  
  CONCLUSIONS
  IPS Empress II core ceramic was significantly stronger than veneering dentin porcelain. Core:dentin thickness ratio could significantly influence the fracture mode and origin, and bilayered IPS Empress II ceramic composite specimens showed little influence in the fracture strength.
authors.affiliation: Department of Prosthetics, Peking University School & Hospital of Stomatology, Beijing 100081, China.
authors.forename: Yi-hong
authors.initials: YH
authors.lastname: Liu
authors.forename: Hai-lan
authors.initials: HL
authors.lastname: Feng
authors.forename: Yi-wang
authors.initials: YW
authors.lastname: Bao
authors.forename: Yan
authors.initials: Y
authors.lastname: Qiu
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002516:Ceramics / Q000737:chemistry*; D019245:Compressive Strength; D003776:Dental Porcelain / Q000737:chemistry*; D004548:Elasticity; D008422:Materials Testing / Q000379:methods*; D018583:Pliability; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D000538:Aluminum Silicates; C075815:IPS-Empress ceramic; D003776:Dental Porcelain