Torsional superelasticity of NiTi archwires.

Angle Orthod

Department of Orthodontics, Nancy Université, Nancy, France.

Published: November 2010

Objective: To reproduce and compare the intraoral torsional behavior of 10 commonly used preformed upper NiTi 0.017 x 0.025 archwires in 0.018-slot brackets at 20 degrees C, 35 degrees C, and 55 degrees C.

Materials And Methods: Ten upper preformed NiTi archwires were compared to a multibraided stainless steel wire. An original testing bench was used to reproduce palatal root torque applied onto an upper central incisor with a maximum value of 1540 g x mm. Ten samples of each wire type were tested at 20 degrees C, 35 degrees C, and 55 degrees C each.

Results: Loading and unloading at 20 degrees C revealed three categories of wires: a group of four NiTi wires of relative stiffness bereft of any superelasticity, a group of six NiTi wires displaying some horizontal plateau, and finally the stainless steel wire of lesser stiffness. Testing at the average oral temperature of 35 degrees C produced the same three categories of wires, with only 2 of 10 NiTi wires displaying a superelastic effect (Copper NiTi 35 degrees C and 40 degrees C). None of the NiTi wires was superelastic at 55 degrees C. Moments increased with temperature as the martensite was replaced by the more rigid austenite.

Conclusion: This study showed that most NiTi wires did not exhibit in torsion the superelastic effect traditionally described in bending. The combination of straight-wire prescriptions and rectangular superelastic NiTi archwires did not provide optimal constant moments necessary to gain third-order control of tooth movement early in treatment. A braided stainless steel rectangular archwire displayed better torsional behavior at 35 degrees C than most NiTi archwires of the same dimensions.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8929502PMC
http://dx.doi.org/10.2319/022310-112.1DOI Listing

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