Nickel release from orthodontic arch wires and cellular immune response tovarious nickel concentrations

Aims: Results from two previous clinical studies suggested that exposure to high nickel-containing orthodontic arch wires may induce hypersensitivity in certain individuals. The purpose of this study was to measure the amount of nickel released from three types of nickel-containing arch wires into a synthetic saliva in vitro, and determine if the concentrations were suffic ient to elicit either cytotoxic (trypan blue exclusion test) or stimulatory (MTT test) responses in human peripheral blood mononuclear cells (PBMCs) d erived from nickel-sensitive and nickel-nonsensitive individuals, PBMCs wer e exposed to five concentrations of nickel sulfate solutions ranging from 0 -29 ppm, and results were compared, particularly at concentrations obtained from nickel release experiments. Findings: The amount of nickel released i nto synthetic saliva ranged from 0.4-4.1 ppb, Wires subjected to a combinat ion of soaking and cyclic straining released significantly more nickel than those that mere soaked only (p less than or equal to 0.05), and NiTi wires released significantly more nickel than did stainless steel or nitrogen-im planted NiTi wires (p less than or equal to 0.05), For PBMCs, significant i ncreased cell proliferation was not observed for any nickel concentration, PBMC cell death rates were highest at nickel concentrations of 29 ppm when the cells were cultured without a cell: growth promoter (p less than or equ al to 0.05), and MTT test values were significantly reduced at both 2.9 and 29 ppm when a growth promoter was included (p less than or equal to 0.05), Conclusion: The maximum amount of nickel released from all tested arch mir es was 700 times lower than the concentrations necessary to elicit cytotoxi c reactions in human PBMCs. (C) 1999 John Wiley & Sons, Inc.