Mechanical properties of several nickel-titanium alloy wires in three-point bending tests

The purpose of this study was to clarify the mechanical properties of 42 br ands of nickel-titanium alloy orthodontic wires from 9 manufacturers by con ducting three-point bending tests under uniform testing conditions. Manufac turers included A-Company, Hoya Medical, Lancer, Ormco, Rocky Mountain, San kin, Tomy (GAC), TP, and 3M/Unitek. Cobalt-chrome, and titanium-molybdenum alloy wires were also tested as a reference for comparison of terce levels. All reported data were recorded during the unloading process to simulate t he force that a wire exerts on a tooth as it is moved into the dental arch from a position of malocclusion. The following results were obtained for th e nickel-titanium wires tested. (Ij Among the 0.016 inch round wires tested under a maximum deflection of 1.5 mm, the difference between the smartest (Copper nickel-titanium 35) and the largest (Aline) load values was 136 g. For the 0.016 x 0.022 inch rectangular wires tested, the difference between the smallest (Copper nickel-titanium 40) and the largest (Aline) load valu es was 337 g. (2) The change in load between 1.5 and 0.5 mm of deflection w as examined to clarify the superelastic properties of the wires tested. For the 0.016 inch wires, 17 wire brands produced a load difference of less th an 100 g, and two brands produced a difference of at least 100 g (Aline and Titanal = 100 g). For the 0.016 x 0.022 inch wires, 15 brands produced a l oad difference of less than 100 g, and eight brands produced a difference o f over 100 g. The smallest and largest load differences were 3 g (Copper ni ckel-titanium 35) and 200 g (Aline). (3) The majority of the samples with a smaller load difference between deflections of 1.5 mm and 0.5 mm in the un loading process were found among super-elastic wires, while samples with a larger load difference were predominantly found among work-hardened wires. Compared with cobalt-chrome and TMA wires, nickel-titanium alloy wires exer t significantly less force. However, the amount of force varies greatly fro m brand to brand. Consequently, when using nickel-titanium alloy wires, bra nds must be selected carefully by taking into consideration the severity of the malocclusion and the stage of orthodontic treatment in each case. It i s the intent of this study to offer clinicians an unbiased guide for the se lection of appropriate nickel-titanium alloy wires.