Aim: (1) To determine the changes in surface roughness that archwires used in lingual orthodontics experience under a non-corrosive environment and (2) to determine the amount of nickel released by them during 30 days.
Subjects and Method: Six different types of lingual orthodontics archwires (Ormco Corp., Glendora, CA, USA) were studied (Respond 0.0175, D-Rect 0.016x0.022, Stainless Steel 0.016, Stainless Steel 0.016x0.022, Nickel Titanium 0.016 and Copper Nickel Titanium 0.017x0.017). They were submerged in Hank's Balanced Salt Solution (HBBS, Sigma-Aldrich Co., 3050 Spruce Street, St. Louis, Missouri) with 0.1 ml of HNO3 at 65% (PANREAC®). The vials were kept at a constant temperature of 37° C for 30 days in a heater. Atomic force microscopy was used to study surface changes in both groups (submerged and non-submerged archwires). Nickel release was measured through atomic absorption spectrometry. Changes in roughness were analysed using a t-test for independent samples.
Results: All archwires except Nickel Titanium wires experienced statistically significant changes in surface roughness after 30 days of immersion (p<0.05), the biggest difference seen in Copper Nickel Titanium. Nickel leaching rate (ng/mm2) during 30 days was the following: Respond (0.0216), D-Rect (0.0013), Stainless Steel 0.016 (0.0036), Stainless Steel 0.016x0.022 (0.0027), Nickel Titanium 0.016 (0.0020) and Copper Nickel Titanium 0.017x0.017 (0.0017).
Conclusions: Changes in surface roughness are statistically significant after immersion in a non-corrosive environment especially for Copper Nickel Titanium archwires. The amount of nickel released was found to be far below the limits known to inflict cell damage for all the archwires.