Comparison of multiforce nickel-titanium wires to multistrand wires without force zones in bending and torque measurements.

Purpose: The aim was to compare rectangular multiforce nickel-titanium (NiTi) wires to rectangular wires with only one force zone. Both types of wires are primarily intended for use during the levelling phase of orthodontic treatment. Thus, basic mechanical properties were examined by means of a three-point bending test. Torque expression, which is dependent on both wire parameters and interslot distances, was analyzed using the Orthodontic Measurement and Simulation System (OMSS).

Material/methods: Four multizone products were tested: DuoForce™ (Forestadent, Pforzheim, Germany), TriTanium™ (American Orthodontics, Sheboygan, WI, USA), Triple Force™ (ODS, Kisdorf, Germany), Bio-Active™ (GC, Breckerfeld, Germany), and two multistrand products without force zones: a nine-strand NiTi, TurboWire™ (Ormco, Orange, CA, USA) and an eight-strand stainless steel (SS) wire, Multibraid™ (GAC, Dentsply Sirona, York, PA, USA). All the wires had the dimension 0.40 mm × 0.56 mm (0.016 inch × 0.022 inch) except the nine-strand NiTi wire TurboWire™, which had a dimension of 0.43 mm × 0.65 mm (0.017 inch × 0.025 inch). Six different bracket systems in the 0.018 inch slot system were chosen: the conventional brackets discovery® and discovery® smart (Dentaurum, Ispringen, Germany), the active self-ligating brackets InOvation™ and InOvation™ mini (GAC, Dentsply Sirona, York, PA, USA) and the passive self-ligating brackets Carrière™ (ODS, Kisdorf, Germany) and BioPassive® (Forestadent, Pforzheim, Germany). The first set-up was a three-point bending test according to DIN EN ISO 15841. For the second experiment, the bracket products glued on a maxilla model were combined with the wire products. The torque moments arising during torqueing of the wires between +20° and -20° were measured in three positions: first incisor, canine and second bicuspid.

Results: Bending tests confirmed variation of the force corresponding to the force zones. The nine-strand NiTi wire TurboWire and the eight-strand SS wire Multibraid™ did not show any variation dependent on the tested area. Torque-moments generated by the multizone wires were higher compared to the braided wires. The nine-strand NiTi wire showed the lowest moments in spite of the higher dimension. As expected, increasing the interbracket distance reduced the torque moments.

Conclusion: The tests verified the existence of multiple force zones in the NiTi wires for forces and moments, respectively. As the torque-moments arising from the multizone wires were rather high, it is not recommended to use these wires as a first "leveling wire" in orthodontic treatment, especially in extremely crowded cases.