DSC analysis and evaluation of forces released on deactivation of orthodontic thermo-activated NiTi wires size 0.40 mm (0.016"): in vitro study

ABSTRACT BACKGROUND: This study evaluated the phase transformation of NiTi orthodontic wires and forces they released on deactivation. METHODS: The structural phase transformations of the following five thermo-activated Nickel Titanium (NiTi) wires: Flexy Thermal Sentalloy® (GAC International), NiTi (35oC) (Eurodonto), Thermo-Plus® (Morelli), FlexyNiTi® Flexy Thermal (35oC) (Orthometric) and Damon® CuNiTi (35oC) (ORMCO Corp.), with cross-sections of 0.40 mm (0.016") were evaluated using Differential Scanning Calorimetry (DSC). In addition, the forces they released were investigated by using the three-point bending test. Five arches of each wire were tested using DSC (-20/80oC at 10oC/min) and six arcs from each wire were sectioned for bending tests. Data were analyzed by ANOVA and a post-hoc Tukey tests. Pearson's correlation test was performed between the results found by the DSC tests and those by three-point analyses (P=.05). RESULTS: The DSC analysis showed that there were differences between the NiTi alloys from every manufacturer, but without differences between lots of the same brand. ORMCO and Orthometric wires showed similar TTR values in cooling (P=.49), and statistically similar in heating (P=.056). The three-point bending test showed different patterns in releasing forces. Correlation was found between the DSC analysis and the three-point bending test results. CONCLUSION: The higher the temperature transformation, larger the variation of force occurred. All wires presented higher Forces at 3mm deflection among 155 (±12.3) and 168.1 (±8) cN. The DSC analysis and the three-point bending test showed that there were differences between the NiTi alloys from every manufacturer.