Interlot variations of transition temperature range and force delivery in copper-nickel-titanium orthodontic wires.

INTRODUCTION: The manufacturing process for copper-nickel-titanium archwires is technique sensitive. The primary aim of this investigation was to examine the interlot consistency of the mechanical properties of copper-nickel-titanium wires from 2 manufacturers. METHODS: Wires of 2 sizes (0.016 and 0.016 x 0.022 in) and 3 advertised austenite finish temperatures (27 degrees C, 35 degrees C, and 40 degrees C) from 2 manufacturers were tested for transition temperature ranges and force delivery using differential scanning calorimetry and the 3-point bend test, respectively. Variations of these properties were analyzed for statistical significance by calculating the F statistic for equality of variances for transition temperature and force delivery in each group of wires. All statistical analyses were performed at the 0.05 level of significance. RESULTS: Statistically significant interlot variations in austenite finish were found for the 0.016 in/27 degrees C (P = 0.041) and 0.016 x 0.022 in/35 degrees C (P = 0.048) wire categories, and in austenite start for the 0.016 x 0.022 in/35 degrees C wire category (P = 0.01). In addition, significant variations in force delivery were found between the 2 manufacturers for the 0.016 in/27 degrees C (P = 0.002), 0.016 in/35.0 degrees C (P = 0.049), and 0.016 x 0.022 in/35 degrees C (P = 0.031) wires. CONCLUSIONS: Orthodontic wires of the same material, dimension, and manufacturer but from different production lots do not always have similar mechanical properties. Clinicians should be aware that copper-nickel-titanium wires might not always deliver the expected force, even when they come from the same manufacturer, because of interlot variations in the performance of the material.