Comparison of nickel-titanium and beta titanium wire sizes to conventional orthodontic arch wire materials.

The theoretical strength, stiffness, and range of nickel-titanium and beta titanium arch wires are compared with several stainless steel or cobalt-chrome wires. With the apparent stiffness as the criterion, equivalent force systems are established in the elastic region between the conventional and the new arch wire alloys. In bending, such calculations show that the nickel-titanium alloy makes superior starting wire, 0.016, 0.018, and 0.018 by 0.018 inch wires having stiffnesses similar to multistranded 0.0175, round 0.012, and 0.014 inch stainless steel wires, respectively, but with about twice the strength and range. By the same method of analysis, the beta titanium alloy makes a particularly good intermediate arch wire, the 0.017 by 0.025 and the 0.019 by 0.025 inch sizes having about twice the stiffness in the horizontal plane but equal rigidity in the vertical plane when compared with 0.016 and 0.018 inch stainless steel. In torsion not even the largest sizes of nickel-titanium (0.021 by 0.025 inch) or beta titanium (0.019 by 0.025 inch) wire meet the stiffness requirements of an 0.019 by 0.026 inch stainless steel wire, thereby making the established alloys the finishing wire of choice.