Evaluation of the biocompatibility of NiTi dental wires: A comparison of laboratory experiments and clinical conditions

• Ex situ biocompatibility experiments were carried out on NiTi dental arch wires.
• Laboratory experiments and actual intraoral conditions were compared.
• The formation of new structures is evident only at later stages of immersion.
• Ex situ experiments successfully simulate C deposition in clinical conditions.
• Ex situ experiments fall short of reproducing wire-bracket contact effect.

Effects of intraoral environment on the surface degradation of nickel-titanium (NiTi) shape memory alloy orthodontic wires was simulated through ex situ static immersion experiments in artificial saliva. The tested wires were compared to companion wires retrieved from patients in terms of chemical changes and formation of new structures on the surface. Results of the ex situ experiments revealed that the acidic erosion effective at the earlier stages of immersion led to the formation of new structures as the immersion period approached 30 days. Moreover, comparison of these results with the analysis of wires utilized in clinical treatment evidenced that ex situ experiments are reliable in terms predicting C-rich structure formation on the wire surfaces. However, the formation of C pileups at the contact sites of arch wires and brackets could not be simulated with the aid of static immersion experiments, warranting the simulation of the intraoral environment in terms of both chemical and physical conditions, including mechanical loading, when evaluating the biocompatibility of NiTi orthodontic arch wires.