Transformation behavior of nickel-titanium orthodontic wires under tensile load

Abstract

This study investigated transformations of nickel-titanium wires using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) under tensile load (100 gf or 500 gf). Two nickel-titanium wires, 35°C Copper Ni-Ti and Nitinol SE, were selected. DSC analyses were performed between –90° and 100°C. Specimens prepared for TMA were approximately 150 μm thick and 12 mm long. TMA analyses were performed between –120° and 100°C. With TMA, all transformation temperatures for a tensile load of 500 gf, obtained from both the heating and cooling curves, were higher than those for a tensile load of 100 gf. While mean A_s and A_f temperatures for Copper Ni-Ti obtained by TMA were much higher than those obtained by DSC analysis, mean M_s and M_f temperatures obtained by TMA were much lower than those obtained by DSC analysis. The transformation behavior of nickel-titanium wires with change in temperature was affected by application of tensile load.