1 Department of Orthodontics, Zanjan University of Medical Sciences, Zanjan, IR Iran

2 Department of Biomaterials Science, Tehran University of Medical Sciences, Tehran, IR Iran

3 Dentist, Tehran, IR Iran


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, 0.014 round, were divided into four groups: 1, Fatigue loading; 2, Fatigue and thermocycling; 3, thermocycling; 4, control. The groups involved in fatigue loading by determined protocol (0.5 mm deflection, 1Hz frequency) also thermocycling performed by this method: bath time (90 seconds), transfer time (15 seconds) and temperature range: 5 - 55C.after these procedure, fatigue and thermocycling effects on the maximum loading force (MLF) and maximum unloading force (MULF) assessed with a 3-point bending test.
Results: In this study, the amounts of MLF in group 1 and 2 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 3 were not different by the group 1 and 2. For the MULF, the results of group 1 and 2 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.