A Review of the Use of Conventional and Temperature-Modulated DSC to Investigate Phase Transformations in Nickel-Titanium Orthodontic Wires

摘要

Nickel-titanium wires are highly important for orthodontics because they deliverrnoptimum light forces for tooth movement. Their clinical performance is directly related to therncharacter and proportions of the austenitic NiTi and martensitic NiTi phases in theirrnmicrostructures. This presentation reviews the phase transformation processes in the three typesrnof commercial nickel-titanium orthodontic wires (nonsuperelastic, superelastic without shapernmemory, and true shape memory in the oral environment) and their effects upon the resultingrnmechanical properties. Thermal analyses have been performed from –125℃ to 100℃ and backrnto–125℃, to reveal the differences in the phase transformations in the forward and reverserndirections. Temperature-modulated DSC has revealed that these transformation processes arernmuch more complex than what has been reported in the past from the use of conventional DSC.rnThe nature of recently reported low-temperature exothermic peaks in the martensitic NiTirnstructure has been established by transmission electron microscopy.