title: Comparison of the microstructure and phase stability of as-cast, CAD/CAM and powder metallurgy manufactured Co-Cr dental alloys.
abstract: OBJECTIVE
  The objective of this study was to identify the different microstructures produced by CC, PM and as-cast techniques for Co-Cr alloys and their phase stability following porcelain firings.
  
  
  METHODS
  Three bi-layer porcelain veneered Co-Cr specimens and one monolithic Co-Cr specimen of each alloy group [cast, powder metallurgy (PM), CAD/CAM (CC)] were manufactured and analyzed using electron backscatter diffraction (EBSD), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Specimens were treated to incremental numbers of porcelain firings (control 0, 5, 15) with crystallographic data, grain size and chemical composition subsequently obtained and analyzed.
  
  
  RESULTS
  EBSD datasets of the cast alloy indicated large grains >200 μm whereas PM and CC alloy consisted of mean arithmetic grain sizes of 29.6 μm and 19.2 μm respectively. XRD and EBSD results both indicated the highest increase in hcp content (>13vol%) for cast Co-Cr alloy after treatment with porcelain firing while PM and CC indicated <2vol% hcp content. A fine grain interfacial layer developed on all surfaces of the alloy after porcelain firing. The depth of this layer increased with porcelain firings for as-cast and PM but no significant increase (p>.05) was observed in CC. EDS line scans indicated an increase in Cr content at the alloy surface after porcelain firing treatment for all three alloys.
  
  
  CONCLUSIONS
  PM and CC produced alloy had superior fcc phase stability after porcelain firings compared to a traditional cast alloy. It is recommended that PM and CC alloys be used for porcelain-fused-to-metal restorations.
authors.affiliation: Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. Electronic address: lika6144@gmail.com.
authors.forename: Kai Chun
authors.initials: KC
authors.lastname: Li
authors.affiliation: Department of Geology, University of Otago, Dunedin, New Zealand.
authors.forename: David J
authors.initials: DJ
authors.lastname: Prior
authors.affiliation: Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand.
authors.forename: J Neil
authors.initials: JN
authors.lastname: Waddell
authors.affiliation: Biomaterials Laboratory, Faculty of Dentistry, University of Sydney, Sydney, Australia.
authors.forename: Michael V
authors.initials: MV
authors.lastname: Swain
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry*; D017076:Computer-Aided Design; D003722:Dental Alloys / Q000737:chemistry*; D003735:Dental Casting Technique; D003793:Dental Restoration, Permanent; D008422:Materials Testing; D008669:Metallurgy; D011208:Powders; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D002858:Chromium Alloys; D003722:Dental Alloys; D011208:Powders
keywords: CAD/CAM; Co–Cr alloy; Crystal structure; EBSD; Electron backscatter diffraction; Metal–porcelain interface; Phase stability; Powder metallurgy