ABSTRACT
Objectives: The shape memory resulting from the superelasticity and thermoelastic effect is the main characteristic of thermally activated NiTi archwires and is closely related to the transition temperature range (TTR). The aim of this study was to evaluate the TTR of thermally activated NiTi archwires commercially available. Material and Methods: Seven different brands of 0.019"x0.025" thermally activated nickel-titanium archwires were tested as received by differential scanning calorimetry (DSC) over the temperature range from -100°C to 150°C at 10°C/min. Results: All thermally activated NiTi archwires analyzed presented stage transformation during thermal scanning with final austenitic temperature (Af) ranging from 20.39°C to 45.42°C. Three brands of NiTi archwires presented Af close to the room temperature and, this way, do not present properties of shape memory and pseudoelasticity that are desirable in clinical applications. Conclusions: The thermally activated NiTi archwires present great variability in the TTR and the elastic parameters of each NiTi archwire should be provided by the manufacturers, to allow achievement of the best clinical performance possible. .
Subject(s)
Nickel/chemistry , Orthodontic Wires , Titanium/chemistry , Transition Temperature , Calorimetry, Differential Scanning , Cold Temperature , Elasticity , Hot Temperature , Materials Testing , Reference ValuesABSTRACT
O efeito de memória de forma dos fios de níquel-titânioestá intimamente relacionado com as temperaturas de transição entreas fases austenítica e martensítica. Este trabalho pretende pormenorizara forma pela qual a temperatura influencia o comportamentomecânico dos fios de Ni-Ti e avaliar o Intervalo de Transição Térmica(ITT) de quatro marcas de fios de Ni-Ti termoativados (Aditek, Morelli,Orthometric e Orthosource). As temperaturas Austenítica inicial (Ai),Austeníticafinal (AO,Martensítica inicial (Mil e Martensítica final (MOforamdeterminadas por meio do método Differential Scanning Calorimetry(DSC). Os gráficos das curvas exotérmicas (formação de martensita)e endotérmicas (formação de austenita) foram obtidos, assim comoos valores das temperaturas de transição térmica. As temperaturas detransformação entre as fases austenítica e martensítica apresentaramgrande variabilidade entre as marcas comerciais testadas, resultandoem um variável efeito de memória de forma.
The memory effect of wire shape is closely relatedto transition temperature among martensitic and austenitic phases.This work intends to discuss the way in which temperature inf)uencesmechanical behavior of Ni-Ti wires and to evaluate Thermal TransitionInterval (ITT) of four different brands of thermal activated Ni-Ti wires(Aditek, Morelli, Orthometric e Orthosource). Initial and final austeniticand martensitic temperatures were obtained by means of DiffentialScanning Calorimetry (DSC). The graphs of exothermic (martensiteformation) and endodermic (austenite formation) curves were obtainedtogether with the values of thermal transition temperatures. The valuesof transformation temperatures between austenitic and martensiticphases did show a great variability among commercial tested brandsand resulted in a variable shape memory effect.