title: Interfacial modulus mapping of layered dental ceramics using nanoindentation.
abstract: OBJECTIVE
  The aim of this study was to test the modulus of elasticity (E) across the interfaces of yttria stabilized zirconia (YTZP) / veneer multilayers using nanoindentation.
  
  
  METHODS
  YTZP core material (KaVo-Everest, Germany) specimens were either coated with a liner (IPS e.max ZirLiner, Ivoclar-Vivadent) (Type-1) or left as-sintered (Type-2) and subsequently veneered with a pressable glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent). A 5 µm (nominal tip diameter) spherical indenter was used with a UMIS CSIRO 2000 (ASI, Canberra, Australia) nanoindenter system to testEacross the exposed and polished interfaces of both specimen types. The multiple point load - partial unload method was used forEdetermination. All materials used were characterized using Scanning Electron Microscopy (SEM) and X - ray powder diffraction (XRD).Emappings of the areas tested were produced from the nanoindentation data.
  
  
  RESULTS
  A significantly (P<.05) lowerEvalue between Type-1 and Type-2 specimens at a distance of 40 µm in the veneer material was associated with the liner. XRD and SEM characterization of the zirconia sample showed a fine grained bulk tetragonal phase. IPS e-max ZirPress and IPS e-max ZirLiner materials were characterized as amorphous.
  
  
  CONCLUSIONS
  The liner between the YTZP core and the heat pressed veneer may act as a weak link in this dental multilayer due to its significantly (P<.05) lowerE. The present study has shown nanoindentation using spherical indentation and the multiple point load - partial unload method to be reliable predictors ofEand useful evaluation tools for layered dental ceramic interfaces.
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, Mile End, London, UK.; Cork University Dental School and Hospital, Wilton, Cork, Ireland.
authors.forename: Antonios L
authors.identifier: 0000-0002-1182-3534
authors.initials: AL
authors.lastname: Theocharopoulos
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, Mile End, London, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bushby
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, Mile End, London, UK.
authors.forename: Ken My
authors.initials: KM
authors.lastname: P'ng
authors.affiliation: School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, Mile End, London, UK.
authors.forename: Rory M
authors.initials: RM
authors.lastname: Wilson
authors.affiliation: Department of Civil and Mechanical Engineering, University of Glasgow, Glasgow, UK.
authors.forename: K Elizabeth
authors.identifier: 0000-0003-2257-0218
authors.initials: KE
authors.lastname: Tanner
authors.affiliation: Barts & The London School of Dentistry, Centre for Adult Oral Health, Stepney Way, Whitechapel, London, UK.
authors.forename: Michael J
authors.identifier: 0000-0002-5561-4531
authors.initials: MJ
authors.lastname: Cattell
keywords: Elastic modulus; Fluorapatite; Zirconia