[Biocompatibility and resistance to corrosion of orthodontic wires]

Various materials are currently used to make orthodontic wires. This article suggests a synthesis on their resistance to corrosion and biocompatibility. In the first part, after a review of some basic notions on the corrosion processes, the authors develop the electrochemical characteristics of the three main groups of alloys used in orthodontics. They study more precisely corrosion resistance of nickel-titanium alloys and, through their own experimental results, they show that this type of alloy is subject to corrosion in acid and fluoridated environment. In the second part, the authors study those alloys biocompatibility. They first mention nickel toxicity and allergy induced by this element. Then, biocompatibility of alloys used in orthodontics is assessed following studies on the release of metallic elements from orthodontic wires, and studies on cell-compatibility when in contact with those wires. It is proved that the state of materials surface has a very high influence on their biocompatibility. As a conclusion, in spite of numerous studies carried out so far, showing a satisfactory biological behaviour of those orthodontic wires, many questions are yet to be answered: long term in vivo performances of those materials have not yet been exactly assessed. Further studies must definitely be carried out.