Cytotoxicity of orthodontic bands, brackets and archwires in vitro

In orthodontic therapy, different materials are used and subjected to a damp oral environment, which can modify their properties. In order to evaluate the biocompatibility of metallic and non-metallic orthodontic appliances their in vitro cytotoxicity has been measured.

Twenty-eight new and nine clinically used materials, including brackets, molar bands and archwires were used. The metallic materials were made of stainless steel, gold-plated steel, pure titanium, nickel-titanium, titanium-molybdenum and silver-based soldering alloy. The non-metallic materials were in polycarbonates and ceramics. After a release period of the material in the culture medium (0.1 mg/ml) for 3 and 14 days, the viability of fibroblasts L929 cultivated with this medium was compared to negative control with MTT assay.

The results showed the non-cytotoxicity of the materials. The metallic and non-metallic materials were similar in terms of cytotoxicity. The cytotoxicity of clinically used samples was equivalent to that of the same non-used samples, except a cytotoxic sample, at 14 days, corresponding to a soldered and clinically used molar band. The 3 day results were different from the 14 day results in six cases out of 37.

In spite of the presence of one cytotoxic sample, the orthodontic materials can be considered as non cytotoxic. However, the practitioner should pay attention to the composition and the polish of soldering silver-based alloys containing copper and zinc in order to limit cytotoxic ion release. The cytotoxicity of the used sample related to ion release might be related to some clinical sub-acute effects related with orthodontic materials, thus a long term release period may be suitable to evaluate in vitro the sub-acute clinical effects of alloys.