title: Chromium release from new stainless steel, recycled and nickel-free orthodontic brackets.
abstract: OBJECTIVE
  To test the hypothesis that there is no difference in the amounts of chromium released from new stainless steel brackets, recycled stainless steel brackets, and nickel-free (Ni-free) orthodontic brackets.
  
  
  METHODS
  This in vitro study was performed using a classic batch procedure by immersion of the samples in artificial saliva at various acidities (pH 4.2, 6.5, and 7.6) over an extended time interval (t(1) = 0.25 h, t(2) = 1 h, t(3) = 24 h, t(4) = 48 h, t(5) = 120 h). The amount of chromium release was determined using an atomic absorption spectrophotometer and an inductively coupled plasma atomic emission spectrometer. Statistical analysis included a linear regression model for repeated measures, with calculation of Huber-White robust standard errors to account for intrabracket correlation of data. For post hoc comparisons the Bonferroni correction was applied.
  
  
  RESULTS
  The greatest amount of chromium was released from new stainless steel brackets (0.52 +/- 1.083 microg/g), whereas the recycled brackets released 0.27 +/- 0.38 microg/g. The smallest release was measured with Ni-free brackets (0.21 +/- 0.51 microg/g). The difference between recycled brackets and Ni-free brackets was not statistically significant (P = .13). For all brackets, the greatest release (P = .000) was measured at pH 4.2, and a significant increase was reported between all time intervals (P < .002).
  
  
  CONCLUSIONS
  The hypothesis is rejected, but the amount of chromium released in all test solutions was well below the daily dietary intake level.
authors.affiliation: Department of Orthodontics, University of Pavia, Pavia, Italy.
authors.forename: Maria Francesca
authors.initials: MF
authors.lastname: Sfondrini
authors.forename: Vittorio
authors.initials: V
authors.lastname: Cacciafesta
authors.forename: Elena
authors.initials: E
authors.lastname: Maffia
authors.forename: Sarah
authors.initials: S
authors.lastname: Massironi
authors.forename: Andrea
authors.initials: A
authors.lastname: Scribante
authors.forename: Giancarla
authors.initials: G
authors.lastname: Alberti
authors.forename: Raffaela
authors.initials: R
authors.lastname: Biesuz
authors.forename: Catherine
authors.initials: C
authors.lastname: Klersy
mesh_terms: D002857:Chromium / Q000737:chemistry*; D003722:Dental Alloys / Q000737:chemistry*; D017743:Equipment Reuse; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D009532:Nickel; D016910:Orthodontic Brackets; D012464:Saliva, Artificial / Q000737:chemistry; D013054:Spectrophotometry, Atomic; D013193:Stainless Steel / Q000737:chemistry*; D013997:Time Factors
chemical_list: D003722:Dental Alloys; D012464:Saliva, Artificial; D002857:Chromium; D013193:Stainless Steel; D009532:Nickel