ON THE VARIABILITY OF CROSS-SECTIONAL DIMENSIONS AND TORSIONAL PROPERTIES OF RECTANGULAR NICKEL-TITANIUM ARCH WIRES

Twenty-five rectangular superelastic or conventional work-hardened nic kel-titanium alloy wires, commonly used in the 0.018-inch edgewise tec hnique, supplied by seven different manufacturers, along with one brai ded nickel-titanium and two beta-titanium wires, were studied with res pect to wire dimensions, edge bevel, and mechanical properties in long itudinal torsion at 37 degrees C. The wires were twisted 25 degrees an d studied in deactivation, simulating application of torque to an indi vidual tooth. Standard Siamese brackets. with stated slot heights of 0 .018 inches and measured slot heights of 0.0187 inches, were used. Mos t wires were within +/-0.0005 inches of the stated dimensions, but had more edge bevel than previously reported for stainless steel and chro me-cobalt alloy wires, Variations in wire dimensions and edge bevel le d to variable torsional (third-order) clearance. The torsional stiffne ss varied among manufacturers within the various wire sizes, this bein g the result of differences in actual cross-sectional geometry and mat erial properties. None of the tested wires exhibited superelastic prop erties under the current conditions, and only one wire had a superelas tic tendency.