Date of Award
Master of Science (MS)
Objective: Conventional nickel-titanium (NiTi) archwires have widespread application in orthodontics due to their unique properties and ability to move teeth with light, continuous forces, but a shortcoming is that they apply near-uniform force along anterior and posterior teeth. Since the force needed to effectively move teeth is a function of the root surface area and bony support, these archwires cause single-rooted teeth to move more than the multi-rooted molars. With the advent of laser-engineered force gradient NiTi orthodontic archwires, individual forces may be applied to different segments or individual teeth of the arch to maximize tooth movement. The aim of this study was to evaluate force distribution and phase transformation properties of a seven-zone force gradient nickel-titanium orthodontic archwire. Materials and Methods: SmartArch™ Laser Engineered CuNiTi archwires (0.016”; Ormco) with seven distinct force zones were investigated. They were compared to the conventional 27°C Superelastic CuNiTi archwires (0.016”; Ormco). A three-point bend test was performed to evaluate mechanical properties and a differential scanning calorimeter (DSC) was used to determine the austenite-finish (Af) temperature for each wire segment from the central incisor to second molar. Data were analyzed via a two-way ANOVA with factors of wire and zone. Results: The 27°C CuNiTi archwire exhibited an overall significantly different (p<0.05) Af than the SmartArch™ wire. As expected, the CuNiTi wire exhibited statistically equivalent (p>0.05) Af temperatures along each zone, whereas SmartArch™ showed significantly different (p<0.05) Af temperatures along each zone, but in a pattern not as expected based upon advertised force values. There were significant differences (p<0.05) for almost all the bending parameters when comparing CuNiTi wires to SmartArch™ wires. As expected, the SmartArch™ wires had statistically different (p<0.05) force values along each zone, but in a pattern inconsistent with advertised force values. The CuNiTi wires also had statistically different (p<0.05) force values among the zones, which was also inconsistent with its advertised properties. Conclusion: Based upon the different Af temperatures and force values, it appears thermal treatment via laser can alter the metallurgy, phase transformation, and mechanical properties of the SmartArch™ orthodontic archwire, but this commercial wire may not exhibit the advertised force distribution.
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