Moment to force ratio characteristics of three Japanese NiTi and TMA dosing loops.

Abstract

OBJECTIVES: This in vitro study investigated the loads ("forces"), moments and moment:force ratios (M:F) generated during activation and deactivation of three closing loop designs constructed from two different orthodontic wire alloys. METHOD: The forces and moments of non-preactivated vertical U-Loops, symmetrical T-Loops, and asymmetrical T-Loops (X-Loops) made from titanium molybdenum alloy (TMA) and Japanese nickel titanium alloy (NiTi) were measured at 35.6 degrees C +/- 0.5 degrees C. The M:F ratios generated during activation and deactivation were calculated for each loop. Analysis of covariance was used to identify statistical differences between loop material and design. RESULTS: The forces, moments and M:F ratios produced by the NiTi closing loops were significantly less than those from the TMA loops. NiTi T-Loops produced a relatively constant force during activation compared to the same design in TMA. The TMA X-loop produced a maximum M:F ratio of 9.4:1. No closing loop produced the optimum M:F ratio required for translational en masse tooth movement. CONCLUSIONS: Optimum M:F ratios for translation are not possible with non-preactivated vertical U-Loops, symmetrical T-Loops, and asymmetrical T-Loops (X-Loops) made of NiTi and TMA alloys.