title: Corrosion in artificial saliva of a Ni-Cr-based dental alloy joined by TIG welding and conventional brazing.
abstract: BACKGROUND
  Fixed prosthesis and partial dental prosthesis frameworks are usually made from welded Ni-Cr-based alloys. These structures can corrode in saliva and have to be investigated to establish their safety.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the corrosion behavior of joints joined by tungsten inert gas (TIG) welding and conventional brazing in specimens made of commercial Ni-Cr alloy in Fusayama artificial saliva at 37°C (pH 2.5 and 5.5).
  
  
  METHODS
  Eighteen Ni-Cr base metal specimens were cast and welded by brazing or tungsten inert gas methods. The specimens were divided into 3 groups (base metal, 2 welded specimens), and the composition and microstructure were qualitatively evaluated. The results of potential corrosion and corrosion current density were analyzed with a 1-way analysis of variance and the Tukey test for pairwise comparisons (α=.05).
  
  
  RESULTS
  Base metal and tungsten inert gas welded material showed equivalent results in electrochemical corrosion tests, while the air-torched specimens exhibited low corrosion resistance. The performance was worst at pH 2.5.
  
  
  CONCLUSIONS
  These results suggest that tungsten inert gas is a suitable welding process for use in dentistry, because the final microstructure does not reduce the corrosion resistance in artificial saliva at 37°C, even in a corrosion-testing medium that facilitates galvanic corrosion processes. Moreover, the corrosion current density of brazed Ni-Cr alloy joints was significantly higher (P<.001) than the base metal and tungsten inert gas welded joints.
authors.affiliation: Dentist, Brazilian Navy, Navy Central Clinic, Rio de Janeiro, Brazil; Department of Dentistry, School of Dentistry, Rio de Janeiro State University, Rio de Janeiro, Brazil. Electronic address: irmacunhamatos@yahoo.com.br.
authors.forename: Irma C
authors.initials: IC
authors.lastname: Matos
authors.affiliation: Professor, Department of Dentistry, School of Dentistry, Rio de Janeiro State University, Rio de Janeiro, Brazil.
authors.forename: Ivan N
authors.initials: IN
authors.lastname: Bastos
authors.affiliation: Professor, Polytechnique Institute, Rio de Janeiro State University, Nova Friburgo, Brazil.
authors.forename: Marília G
authors.initials: MG
authors.lastname: Diniz
authors.affiliation: Professor, Mechanic Engineering Department, Rio de Janeiro State University, Rio de Janeiro, Brazil.
authors.forename: Mauro S
authors.initials: MS
authors.lastname: de Miranda
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000388:Air; D001128:Argon; D002858:Chromium Alloys / Q000032:analysis / Q000737:chemistry*; D003343:Corrosion; D003775:Dental Polishing / Q000379:methods; D012994:Dental Soldering / Q000379:methods*; D058266:Dielectric Spectroscopy; D004563:Electrochemistry; D006358:Hot Temperature; D006851:Hydrochloric Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008669:Metallurgy / Q000379:methods; D008855:Microscopy, Electron, Scanning; D017942:Nitric Acid / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D013696:Temperature; D014414:Tungsten
chemical_list: D002858:Chromium Alloys; D012464:Saliva, Artificial; D017942:Nitric Acid; D001128:Argon; D006851:Hydrochloric Acid; D014414:Tungsten