Diamond-like carbon (DLC) film has been coated onto nickel-titanium alloy orthodontic archwires using an arc discharge ion plating process to prevent corrosion and nickel ion release from the orthodontic archwires. Nickel ion release was observed in the immersion test in physiological saline at 85 degrees C for 5 days. The amount of the nickel ion release was measured by using microwave-induced plasma mass spectroscopy, and for the DLC film-coated samples, the nickel ion release level was 50 ppb. The DLC film coating reduced the nickel ion release level by 80%. Additionally, human adult gingival fibroblasts were used in a cell culture to investigate the effect of nickel ion release on cell growth. As a result, the DLC film coating suppressed the influence of the nickel ion release to the cell culture. DLC films are suitable for circumventing the problem of nickel ion release from nickel-titanium alloy orthodontic archwires. (c) 2005 Elsevier B.V. All rights reserved.