Deterioration in the superelasticity of Ti sputter coated on NiTi orthodontic wire

Abstract

To evaluate the deterioration in the superelasticity of Ti‐coated NiTi orthodontic wires, titanium was coated onto wires to form a 1‐μm thick film using radio frequency magnetron sputtering. In superelasticity cycle tests, the σ_5.0 value (the stress at 5.0% strain) of a Ti‐coated wire was lower than that of a non‐coated wire by 6.2% after one cycle, and by 10.4% after 20 cycles. In a three point bend tests, the L_2.0 value (the load at 2.0 mm deflection) of a Ti‐coated wire was 2.55 N, and this was reduced by 39.0% of the L_2.0 value of a non‐coated wire (4.18 N).

After the non‐coated and the Ti‐coated wires had been immersed in physiological saline for periods of four and eight weeks, the concentration of Ni ions released into each solution was detected using MIP‐Mass, and Ni peak intensity of the wires was measured using XPS. After eight weeks, the concentration of Ni ions released from the non‐coated and the Ti‐coated wires was 657 and 135 ppb, respectively. In a clinical test, no inflammation was observed during the entire attached period of four weeks in both the non‐coated and the Ti‐coated wire. In the Ti‐coated wire, little exfoliation of the Ti‐coating was observed using SEM and EDS. It was concluded that Ti‐coated NiTi orthodontic wire has much potential for its application, with a low probability of causing any Ni allergy.