In-vitro Assessment of Cytotoxicity from Metal Ion Release in Corroding Fixed Orthodontic Appliances

Metallic corrosion of orthodontic appliances occurs due to potentially damaging physical and chemical agents. The major corrosion products of stainless steel are iron, chromium, and nickel. When tissues are exposed to certain concentrations of a primary irritant for certain periods, cytotoxic effects may be observed. Hence, this study aimed to assess the cytotoxicity of nickel, iron, and chromium ions during fixed orthodontic treatment onto human keratinocytes (HaCaT).

The metal ions nickel, chromium, and iron in concentrations of 75, 150, 300, 600, 1200, and 2400 μg/ml were prepared to assess the cytotoxicity on HaCaT cells. The control group included these metal ions at 0 μg/ml. Cytotoxicity was assessed by microculture tetrazolium (MTA) assay. The half maximal inhibitory concentration (IC50) was measured and a scanning electron microscope (SEM) was used to assess the morphological changes of the HaCaT cells. The Kruskal-Wallis test followed by the Bonferroni’s post hoc test was carried out to determine the difference in percentage inhibition within and between the groups at various concentrations.

Nickel showed the highest cytotoxic effects in comparison with other metal ions.  Iron hexahydrate, nickel hexahydrate, and chromium hexahydrate have shown an IC50 value of 552.4 μg/ml, 364.1 μg/ml, and 641.1 μg/ml inhibition in HaCaT cells respectively. Cytotoxic effects were dose dependent on the tested materials. Comparison of percentage inhibition between groups showed a p-value of 0.372.

The present study showed that the nickel, chromium, and iron ions induced a wide range of toxicity to human keratinocytes. The IC50 values ranged between 364.1 and 641.1. Nickel was the most toxic metal tested between the concentrations of 75 to 2400 μg/ml for HaCaT cells compared to other metal ions used in the study.