Effects of steam and dry-heat sterilization on bending properties of NiTi wires

Abstract

Purpose Nickel–titanium arch wires have a prominent role in orthodontic appliances due to their desirable mechanical properties. The purpose of the present study is to determine the effects of autoclave and dry-heat sterilization on the bending properties of three types of NiTi superelastic wires. Methods In this experimental study, three commercial types (Force I, Rematitan LITE, and G & H) of superelastic NiTi wires, 0.016 in. in diameter, were selected. From each type of wire, 20 specimens were prepared. The specimens were initially subjected to the three-point bending test at a rate of 1 mm/min on the Dartec testing machine in order to determine their load-deflection properties before sterilization. Then, 10 specimens of each type of wire were subjected to dry-heat sterilization (160 °C, 120 min) and 10 to autoclave sterilization (121 °C, 15 psi, 24 min). After sterilization, the specimens were subjected to the three-point bending test again and their load-deflection curves were plotted. The values for bending properties obtained before and after sterilization were subjected to the Duncan and ANOVA tests at the 0.05 significance level. Results Our findings revealed considerable changes in the load-deflection properties of the test wires as a result of dry-heat sterilization. These changes included decreasing in applied force in both loading and unloading phases and reducing of wire superelasticity. Conclusion Steam and dry-heat sterilization cause changes in the mechanical properties of superelastic NiTi arch wires.