Comparative Study of Load/Deflection Rates of Nickel-Titanium Rectangular Orthodontic Wires

OBJECTIVES: The purpose of this study was to compare the ratios of load and deflection of different trademarks of nickel-titanium rectangular orthodontic wires. METHODS: The sample comprised 10 pre-contoured wires (5 conventional and 5 heat-activated) from each one of the following trademarks: Abzil Lancer, Morelli, 3M Unitek and Ormco, with a transversal section of .019” x .025”. The mechanical tests were performed with a universal essay machine EMIC 10000, provided with a steel tip that transmitted progressive loads to the selected wires. Simultaneously, a computer software registered the deflections of the wires and automatically generated tables of load and deflection ratios, thus, making it possible to analyze the stiffness of the different wires. The student “t” test (p<0.05) was employed to evaluate the statistically significant differences between wire stiffness of different trademarks. RESULTS: As far as it concerns to conventional nickel-titanium orthodontic wires, the smallest load/deflection ratios were observed for 3M Unitek wires, followed by Ormco, whereas Morelli and Abzil Lancer wires exhibited similar load/deflection ratios. On the other hand, heat-activated wires that revealed the smallest load/deflection ratios were those of Ormco, followed by 3M Unitek, Abzil Lancer and Morelli. Furthermore, these last three trademarks presented similar results between them. CONCLUSIONS: The more flexible conventional nickel-titanium orthodontic rectangular wires were those manufactured by 3M Unitek and Ormco, and this last trademark also revealed the greatest flexibility between heat-activated ones, releasing gentle forces in relation to comparatively greater deflections