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The effect of long-term deflection on permanent deformation of nickel-titanium archwires.

The clinician must now consider the alloy along with cross-sectional shape and size when selecting archwires. The purpose of this study is to quantify permanent deformation after long-term deflection of available nickel-titanium archwires. Nine nickel-titanium, one beta-titanium and one stainless steel archwires, .016 inch round, were deflected into orthodontic brackets of simulated archform. One lateral incisor was positioned to yield a deflection of 5 mm in a lingual direction. After wire deactivation, deformation was measured at 1, 14, and 28 days. Two-way ANOVA and Tukey's critical difference tests were used to determine statistical differences. The nickel-titanium wires exhibited better springback characteristics and less permanent deformation than the stainless steel and TMA wires. Several wires increased deformation as deflection time increased. No clinically significant difference was found between presently available nickel-titanium wires in terms of permanent deformation, long- or short-term.