Temperature effects on the forces, moments and moment to force ratio of nickel-titanium and TMA symmetrical T-loops

Abstract

Objective: To test the null hypothesis that temperature has no effect on the force, moment, and moment to force ratio (M:F) of nickel-titanium (NiTi) and titanium molybdenum alloy (TMA) T-loops. Materials and Methods: Twelve symmetrical T-loops were constructed from NiTi and TMA rectangular wires (N = 24). For each material, four specimens had 30° preactivation bent into the legs, four had 15°, and the remainder no preactivation. The specimens were mounted on a custom stand incorporating a force and a moment transducer housed in an insulated oven in which the temperature was varied from 10°C to 50°C in 10° increments (±0.5°C). The loops were opened in 1-mm increments to a maximum of 8 mm and allowed to return to the rest position. Forces and moments were recorded at each interval; from this, the M:F was calculated. Mixed-model statistical analysis was used to detect differences between mean results of material type, preactivation, and temperature. Results: Temperature significantly influenced the forces and moments (P < .000) produced by NiTi closing loops, with values increasing as the temperature increased. The M:F ratios of NiTi loops were less affected, with no significant changes with temperature for the 15° and 30° preactivation loops, although some change was noted for the non-preactivated loops. TMA wires showed significance for some force measurements, but were generally not influenced by temperature. Conclusion: The hypothesis is rejected. Temperature significantly affected the forces and moments produced by NiTi T-loops, though these changes generally do not affect the overall M:F ratio. © 2008 by The EH Angle Education and Research Foundation, Inc.