Effect of direct electric resistance heat treatment on mechanical properties of NiTi orthodontic arch wires

Abstract

Two types of rectangular orthodontic archwires; NiTi™ and 40°CuNiTi, were heat treated by Direct Electric Resistance Heat Treatment (DERHT) using different electric currents for 4 s. Their mechanical properties were then evaluated by micro hardness and three-point bending tests. After applying 4.5-5.5 A current, the hardness of NiTi™ increased with the increased current, whereas the change in hardness of 40°CuNiTi was slight. When 6 A current was applied, the hardness of the midspan of both wires significantly decreased. From the three-point bending test, unloading forces of NiTi™ increased after treating with 5.5 A current, while those of 40°CuNiTi decreased. However, both specimens lost their superelasticity when applied with 6 A current. In conclusion, after DERHT, various changes in mechanical properties can be noted in the different types of nickel titanium archwire. © 2008 Trans Tech Publications, Switzerland.