title: Fracture toughness improvements of dental ceramic through use of yttria-stabilized zirconia (YSZ) thin-film coatings.
abstract: OBJECTIVE
  The aim of this study was to evaluate strengthening mechanisms of yttria-stabilized zirconia (YSZ) thin film coatings as a viable method for improving fracture toughness of all-ceramic dental restorations.
  
  
  METHODS
  Bars (2mm×2mm×15mm, n=12) were cut from porcelain (ProCAD, Ivoclar-Vivadent) blocks and wet-polished through 1200-grit using SiC abrasive. A Vickers indenter was used to induce flaws with controlled size and geometry. Depositions were performed via radio frequency magnetron sputtering (5mT, 25°C, 30:1 Ar/O2 gas ratio) with varying powers of substrate bias. Film and flaw properties were characterized by optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Flexural strength was determined by three-point bending. Fracture toughness values were calculated from flaw size and fracture strength.
  
  
  RESULTS
  Data show improvements in fracture strength of up to 57% over unmodified specimens. XRD analysis shows that films deposited with higher substrate bias displayed a high %monoclinic volume fraction (19%) compared to non-biased deposited films (87%), and resulted in increased film stresses and modified YSZ microstructures. SEM analysis shows critical flaw sizes of 67±1μm leading to fracture toughness improvements of 55% over unmodified specimens.
  
  
  CONCLUSIONS
  Data support surface modification of dental ceramics with YSZ thin film coatings to improve fracture toughness. Increase in construct strength was attributed to increase in compressive film stresses and modified YSZ thin film microstructures. It is believed that this surface modification may lead to significant improvements and overall reliability of all-ceramic dental restorations.
authors.affiliation: Department of Materials Science and Engineering, North Carolina State University, 911 Partner's Way, Raleigh, NC 27695, USA.
authors.forename: Ryan N
authors.initials: RN
authors.lastname: Chan
authors.forename: Brian R
authors.initials: BR
authors.lastname: Stoner
authors.forename: Jeffrey Y
authors.initials: JY
authors.lastname: Thompson
authors.forename: Ronald O
authors.initials: RO
authors.lastname: Scattergood
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Piascik
mesh_terms: D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D017655:Silicon Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D017554:Carbon Compounds, Inorganic; D020099:Coated Materials, Biocompatible; D003764:Dental Materials; C454801:ProCAD Ceramic; D017655:Silicon Compounds; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide; C022088:silicon carbide
keywords: All-ceramic; Dental material; Failure; Fracture toughness; Stress; Thin film; Zirconia