title: Identification of monoclinic phase in CAD/CAM zirconia FPD frameworks.
abstract: OBJECTIVE
  The aim of this study was to identify the presence of monoclinic zirconia phase (m-ZrO2) in 5 computeraided design/computer-assisted manufacture zirconia systems composed of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP).
  
  
  METHODS
  Three-unit fixedpartial dentures were prepared from Cercon (CR); Lava (LW); Zenotec Zr Bridge (WD); In-Ceram YZ (YZ); and IPS e-max ZirCAD (ZC), all milled in a pre-sintered stage and then fully sintered according to the manufacturers' instructions. Raman spectroscopy was used to identify and map the distribution of the m-ZrO2 phase at cervical crown margins, pontic and connector regions. Three sets of data were obtained from each material (n = 2) and the percentage volume (%Vm) of the m-ZrO2 phase was calculated per region. Statistical analysis was performed by two-way analysis of variance and Tukey test (a = 0.05).
  
  
  RESULTS
  The m-ZrO2 phase was detected in all the specimens, with the highest intensity located at the crown margins. WD showed the lowest %Vm content (0- 3.14%), followed by LW (10.26-12.39%), CR (11.72-13.19%), ZC (11.13-14.10%) and YZ (12.15-14.99%). No statistically significant difference was found among LW, CR, ZC, YZ per region. Within each material group, significant differences were found between margin-pontic/connector (WD, YZ), margin-connector (CR, ZC) and margin-pontic (LW).
  
  
  CONCLUSIONS
  The Y-TZP destabilizing m-ZrO2 phase was identified in all the fully sintered frameworks tested, with the highest %Vm located at the margins. The extent to which the presence of this phase may be implicated with zirconia low temperature degradation or porcelain to zirconia bonding is unknown.
authors.affiliation: Department of Prosthodontics, University of Athens, Athens, Greece.
authors.forename: Villy
authors.initials: V
authors.lastname: Kypraiou
authors.forename: Stavros
authors.initials: S
authors.lastname: Pelekanos
authors.forename: George
authors.initials: G
authors.lastname: Eliades
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003460:Crystallization; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D003779:Denture Design; D003830:Denture, Partial, Fixed; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D044367:Phase Transition; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C485633:In-Ceram Zirconia; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium