title: Electrochemical impedance investigation of Ni-free Co-Cr-Mo and Co-Cr-Mo-Ni dental casting alloy for partial removable dental prosthesis frameworks.
abstract: BACKGROUND
  The pH level of the oral environment influences corrosion in dental materials. Corrosion behaviors of Co-Cr-Mo and Co-Cr-Mo-Ni alloys in different pH environments remain undetermined.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the surface properties and corrosion behaviors of Co-Cr-Mo and Co-Cr-Mo-Ni dental casting alloys in artificial saliva at pH values of 5.0 and 2.5.
  
  
  METHODS
  Fifty specimens were divided into 2 groups according to the alloy composition. The surface compositions, hardness values, and microstructures of the alloys were measured before immersion in artificial saliva. The corrosion behaviors of the specimens in artificial saliva at pH values of 5.0 and 2.5 were studied using electrochemical impedance spectroscopy (EIS). The microstructures were examined again after a 7-day immersion test. Data were analyzed by a 1-way analysis of variance (ANOVA) test (α=.05).
  
  
  RESULTS
  As expected, the relative levels of Co and Cr of the surface composition were higher in the Co-Cr-Mo alloy. The Co-Cr-Mo alloy had statistically higher surface hardness than the Co-Cr-Mo-Ni alloy (P<.05). In the pH 2.5 environment, both of the alloys showed decreased corrosion resistance (P<.05). The microstructure of the Co-Cr-Mo-Ni alloy corroded more than that of the Co-Cr-Mo alloy in the pH 2.5 environment. The oxide-layer corrosion resistance of the Co-Cr-Mo alloy was better than that of the Co-Cr-Mo-Ni alloy in Fusayama artificial saliva solutions at pH values of both 5.0 and 2.5 (P<.05).
  
  
  CONCLUSIONS
  The corrosion resistance of the Co-Cr-Mo alloy was better in the oral environment, especially at a low pH value.
authors.affiliation: Doctoral candidate, Department of Prosthodontics, School of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, People's Republic of China.
authors.forename: Chao
authors.initials: C
authors.lastname: Qian
authors.affiliation: Doctoral candidate, Department of General Dentistry, School of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, People's Republic of China.
authors.forename: Xingchen
authors.initials: X
authors.lastname: Wu
authors.affiliation: Professor, Department of Prosthodontics, School of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, People's Republic of China.
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Physician-in-charge, Department of Prosthodontics, School of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, People's Republic of China. Electronic address: ywqhuai@126.com.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Yu
mesh_terms: D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry* / Q000627:therapeutic use; D003735:Dental Casting Technique; D003832:Denture, Partial, Removable; D017097:Electric Impedance; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009532:Nickel / Q000737:chemistry / Q000627:therapeutic use; D013499:Surface Properties; D014800:Vitallium / Q000737:chemistry* / Q000627:therapeutic use
chemical_list: D003722:Dental Alloys; D014800:Vitallium; D009532:Nickel