Aim: To assess whether the forces created by the magnetic resonance imaging (MRI) field cause a deflection of orthodontic stainless steel archwires or a change of their mechanical properties. Methods: Sixty stainless steel 0.016-inch archwires were divided into three groups of 20 wires each. The control group was as received from the manufacturer, the MRI 1 group had wires attached to brackets on artificial teeth subjected to MRI (1.5 Tesla), and the MRI 2 group had activated T-loops subjected to MRI (1.5 Tesla). The mechanical properties were compared between the control group and MRI 1 group, whereas in the MRI 2 group, the change in the amount of activation was measured. The data were evaluated by repeated measurement analysis with independent and paired t tests. Results: Tensile strength did not differ significantly between the control group and the MRI 1 group (P = .64). In the MRI 2 group, the mean distance between the vertical loop legs before and after MRI did not differ significantly (P = .53). Conclusion: The magnetic field did not significantly affect the mechanical properties of the tested stainless steel wires, nor did it change the loop activation. World J Orthod 2010;11:e72–e77.

Key words: orthodontic wires, magnetic resonance imaging, stress, strain, tensile strength