Surface analysis of nickel-titanium archwire used in vivo.

OBJECTIVES: The surface quality of an archwire is a critical factor in the prevention of corrosion. This study was conducted to evaluate and assess the surface of as-received and used nickel-titanium archwires for evidence of corrosion, and to analyze possible corrosion products. METHODS: Round 0.4 mm and square 0.4 mm x 0.55 mm nickel-titanium archwires from two manufacturers were subjected to elemental analysis, examined, and photographed in a scanning electron microscope with an EDAX unit. The used wires had been in service from 3 wk to 4 mon. There were no systematic differences in surface topography or composition between the as-received and used wires. RESULTS: The examination revealed undulated surfaces with manufactural scratches and crevices. The surface quality within the same archwire varied slightly, with different smoothness in the anterior and posterior regions. No systematic discernible difference was found between used and as-received arch wires. The analyses of different areas on the used archwires revealed no differences in the metal composition. SIGNIFICANCE: The surface defects found on the as-received wires were evidently not large enough to act as sites for corrosion attack.

Proliferation of nickel-sensitive human lymphocytes by corrosion products of orthodontic appliances.

Lymphocyte transformation tests were performed on peripheral blood taken from individuals with a history of contact dermatitis who also presented with a positive patch test to nickel sulphate, and from individuals with no history of contact dermatitis. The results implied that nickel leached out from metallic orthodontic appliances in sufficient amounts and of a chemical nature adequate to stimulate proliferation of lymphocytes from some of the nickel-sensitive subjects.

Cytotoxic and antibacterial effects of orthodontic appliances.

The cytotoxic and antibacterial effects of orthodontic appliances were assessed. Metallic devices used in orthodontics, such as molar bands, brackets, and archwires were tested by the agar overlay cytotoxicity test with mouse fibroblast cells. The same devices were tested for antibacterial effect with Streptococcus mutans and S. sanguis. The multicomponent devices, which are bonded with silver- and copper-based brazing alloys, were more cytotoxic than the single-component devices, probably because copper is more cytotoxic than nickel. The devices had a definite, but low, antibacterial effect, as compared with the 0.05% chlorhexidine positive control. A cytotoxic effect of the devices per se might contribute to a localized gingivitis. It is uncertain whether orthodontic devices have any significant inhibitory effect on dental plaque viability.

Composition and in vitro corrosion of orthodontic appliances.

The high incidence of nickel allergy and the increasing use of nickel-containing dental biomaterials has been of growing concern. The purpose of this investigation was to analyze different types of alloys used in orthodontics, and to study whether nickel and chromium will be released from these alloys when stored in physiologic saline. Face-bows, brackets, molar bands, and arch wires were analyzed. Most of the different parts in the face-bows, brackets, and molar bands were similar to conventional 18/8 stainless steel. Except the wires, most appliances included a variable amount of silver solder, the greatest in face-bows. After 14 days in 0.9% sodium chloride (NaCl), the largest amount of nickel and chromium were leached out from the face-bows and the least amount from the arch wires. Soldered stainless steel face-bows seemed to be very susceptible to corrosion. The release of nickel seemed to be related to both the composition and the method of manufacture of the appliances, but the release was not proportional to the nickel content.

Cytotoxic effect of orthodontic appliances.

The use of orthodontic appliances may contribute to local gingivitis, often attributed to increased plaque retention. Gingivitis of bacterial origin cannot clinically be distinguished from local tissue irritation caused by corrosion products. The purpose of this investigation was to assess the cytotoxic effect of various metallic components used in orthodontics. Multicomponent devices such as facebows, molar bands, and brackets along with single-component brackets and archwires were tested by the agar overlay cytotoxicity test with mouse fibroblast cells. None of the archwires caused any cytotoxic effect, even though some contained 54 per cent nickel. However, the multi-component devices, which were joined with silver- and copper-based brazing alloys were more cytotoxic than the single-component devices. Copper is more cytotoxic than nickel, which could explain the greater cytotoxic effect of the samples with brazing materials. It is speculated that cytotoxic corrosion products from orthodontic appliances might contribute to localized gingivitis.