Relationship between A_f Temperature and Load Changes in Ni-Ti Orthodontic Wire under Different Thermomechanical Conditions

抄録

Simple three point bending tests were performed on Ni-Ti wires with three different A_f points (1°C, 13°C and 34°C) to clarify the relationship between A_f temperature and load changes under constant deformation. Each wire was deformed at 37°C and then thermal changes were imposed by temperatures of 2°C or 60°C. The load changes with thermal changes from 37°C to 2°C or 60°C showed the same tendency on the wires with different A_f points: In the loading stage, the load became lower than the initial level at 37°C and in the unloading stage, the load became higher than the initial load. The largest load change in the unloading stage was measured with the 13°C A_f point wire. Care must be taken when handling Ni-Ti wire with an A_f point of less than 1°C in order to prevent it from reaching the limit of critical stress of slip deformation when the temperature in the mouth rises to above 40°C.