Nickel release from new conventional stainless steel, recycled, and nickel-free orthodontic brackets: An in vitro study

IntroductionThe aim of this study was to compare the nickel released from 3 kinds of orthodontic brackets: new conventional stainless steel, recycled stainless steel, and nickel-free brackets.MethodsThis in-vitro study was performed by using a classic batch procedure. Samples were immersed in artificial saliva at various acidities (pH 4.2, 6.5, 7.6) over an extended time interval (0.25, 1, 24, 48, and 120 hours). The amount of nickel released was determined by 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.ResultsThe recycled brackets released the most nickel (74.02 ± 170.29 μg per gram); the new stainless steel brackets released 7.14 ± 20.83 μg per gram. The nickel-free brackets released the least nickel (0.03 ± 0.06 μg per gram). All the differences among the groups were statistically significant (P = 0.000).ConclusionsReconditioned brackets released the most nickel. Moreover, the highest nickel release was recorded in the 2 experiments performed at pH 4.2; it was lower at pH 6.5 and 7.6. Conversely, no relevant differences were observed overall between the maxillary and mandibular arches.