The Evaluation of the Fatigue and Thermocycling Effects on the Maximum Loading and Unloading Force of the CuNiTi Wire

Background: In the oral environment orthodontic wires will be subjected to thermal fluctuations and repeated loading (fatigue). Objectives: The aim of this study is to evaluate the thermocycling and fatigue effect on the CuNiti wires. Materials and Methods Samples of CuNiti wires, ۰.۰۱۴ round, were divided into four groups: ۱, Fatigue loading; ۲, Fatigue and thermocycling; ۳, thermocycling; ۴, control. The groups involved in fatigue loading by determined protocol (۰.۵ mm deflection, ۱Hz frequency) also thermocycling performed by this method: bath time (۹۰ seconds), transfer time (۱۵ seconds) and temperature range: ۵ - ۵۵C.after these procedure, fatigue and thermocycling effects on the maximum loading force (MLF) and maximum unloading force (MULF) assessed with a ۳-point bending test. Results In this study, the amounts of MLF in group ۱ and ۲ were significantly different with themselves and control group, but in the control group, the results were not significantly different with thermocycling group. Also the amounts of MLF in the group ۳ were not different by the group ۱ and ۲. For the MULF, the results of group ۱ and ۲ were significantly different with the control and thermocycling group. Difference between fatigue and control groups for hysteresis loading (difference between MLF and MULF) variable was not significant while other two by two comparisons were significant. Conclusions The fatigue loading increased MLF and MULF, but the effect of thermocycling was complicated on the MLF. Thermocycling also did not affect the MULF, but decreased hysteresis loading.

Keywords:

CuNiTi Alloy , CuNiTi Wires , Orthodontic Wires , Hysteresis Loading , Load Deflection Rate (LDR)