S. M. S. Aghamiri, M. nili Ahmadabadi, S. Raygan, University of Tehran, Tehran, Iran
NiTi wires have been used in orthodontic application because of their unique characteristics. The mechanical properties of wires should result in achieving continuous optimal forces and rapid tooth movement. Magnitude of hysteresis loop attributes to energy dissipative processes and the stress hysteresis specifies the limit of irreversible phenomena that happen during stress induced martensite (SIM) transformation. This investigation was carried out to examine stress hysteresis behavior of nickel-titanium archwires in different temperatures. Two different brands of NiTi archwires including TrueFlex (superelastic wire) and Copper NiTi (shape memory wire) were studied by three-point bending test in 4 mm deflection. Each test was done in three clinically relevant temperatures of 22, 37 and 50 °C. Differential scanning calorimetry (DSC) analysis was performed to determine the phases and transformation temperatures in wires. The results show that there are considerable and meaningful differences between the hysteresis of wires in each situation.
Summary: 1- Truflex wire shows B2-R-B19´ transformation but Copper NiTi wire demonstrates B2-B19´ transformation.
2- Copper NiTi wire transformed to martensite at 22°C with considerable residual strain, but has superelastic behavior at 37°C and 50°C.
3- Stress hysteresis of both wires increased with increasing test temperature.
4- The plateaue force of Wires increased according to clausius-clapeyron equation.
