Evaluation of nickel ion release from various orthodontic arch wires: An in vitro study

The high incidence of nickel (Ni) allergy and the increasing use of Ni-containing dental biomaterials have been of growing concern. The purpose of this investigation was to analyze and evaluate the rate of Ni ion release from different types arch wires used in orthodontics.

Four groups of arch wires (nickel titanium [NiTi], SS, Cu NiTi and ion implanted NiTi) with twelve samples were stored in artificial saliva with a pH 5.6-7.0 thermostated at (36.5°C) and tested at different intervals i.e., 7(th) day, 14(th) day, and 21(st) day. The amount of Ni and Ti ions released from the sample were evaluated using an atomic adsorption spectrophotometer. The solution was replaced with a fresh bottle to avoid sediments.

Statistical analysis was performed by nonparametric tests (Student's paired t-test, one-way analysis of variance and multiple comparison test by Tukey "Honestly significant difference"). The statistical package SPSS PC plus (version 4.0.1) was used for data processing and statistical analysis. Results showed significantly statistical influence on the release amount of Ni and Ti ions. Large variation in concentration of Ni released from brackets and bands combined. However, the amount of Ni ions released in all test solutions diminished with time and was below the critical value necessary to induce allergy and below daily dietary intake level.

The daily release of NiTi, SS, Cu NiTi and ion implanted NiTi by an orthodontic appliance in acid pH, particularly favorable to corrosion, was well below that ingested with a normal daily diet. It is therefore concluded that the quantities of metal ions released in our experimental conditions should not be cause for concern in utilizing the appliance.