title: Flexural strength of a layered zirconia and porcelain dental all-ceramic system.
abstract: BACKGROUND
  New processing techniques have facilitated the use of zirconia core materials in all-ceramic dental prostheses. Zirconia has many potential advantages compared to existing core materials; however, its performance when layered with porcelain has not been evaluated.
  
  
  OBJECTIVE
  This study investigated the strength of a wide variety of layered zirconia and porcelain beams to determine whether the inclusion of zirconia cores results in improved strength.
  
  
  METHODS
  Eight types of layered or simple zirconia and porcelain beams (n = 10), approximately fixed partial denture-size, were made of a tetragonal polycrystalline zirconium dioxide partially stabilized with yttria core (Lava System Frame) and a feldspathic dental porcelain (Lava Ceram veneer ceramic). Elastic moduli of the materials were measured using an acoustic method. Maximum force and modulus of rupture were determined using 3-point flexural testing and a universal testing machine. Descriptive statistical methods were used.
  
  
  RESULTS
  Beams with porcelain tensile surfaces recorded mean tensile strengths or moduli of rupture from 77 to 85 MPa, whereas beams with zirconia tensile surfaces recorded moduli of rupture almost an order of magnitude higher, 636 to 786 MPa. The elastic moduli of the porcelain and zirconia materials were 71 and 224 GPa, respectively. Crack propagation following initial tensile cracking often involved the porcelain-zirconia interface, as well as bulk porcelain and zirconia.
  
  
  CONCLUSIONS
  The layered zirconia-porcelain system tested recorded substantially higher moduli of rupture than have been previously reported for other layered all-ceramic systems.
authors.affiliation: University of California Los Angeles, School of Dentistry, Los Angeles, CA 90095-1668, USA. snwhite@ucla.edu
authors.forename: S N
authors.initials: SN
authors.lastname: White
authors.forename: V G
authors.initials: VG
authors.lastname: Miklus
authors.forename: E A
authors.initials: EA
authors.lastname: McLaren
authors.forename: L A
authors.initials: LA
authors.lastname: Lang
authors.forename: A A
authors.initials: AA
authors.lastname: Caputo
mesh_terms: D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D004548:Elasticity; D008422:Materials Testing; D018583:Pliability; D013718:Tensile Strength; D015019:Yttrium; D015040:Zirconium
chemical_list: C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide