Comparison of Torque Angles in Wide and Narrow Edgewise Brackets

Objectives: Compare torque angles in wide [upper] (WD) and narrow [lower] (N) central incisor brackets in non-torqued slots with 18X25 mil arch-wires: stainless steel (SS), nickel-titanium (NT), and tungsten-molybdenum (TMA). Hypotheses: (1) that a torque angle with a force similar to published recommendations acted similarly in WD and N brackets, and (2) that there is no difference in torque angles among three arch-wire alloys in either WD or N brackets.
Methods: A machine recorded torque angles (in degrees) for central incisors (n=5/per group). The force at the machine wheel was 67 grams and at the wire was 43.25 N-mm. One-way ANOVA with post-hoc Tukey’s HSD was conducted to test for the differences in torque angles among the three types of arch-wire alloys in WD and N brackets, and a paired-sample t-test was used to detect differences between WD and N brackets within each arch-wire alloy (alpha = 0.05).
Results: Both hypotheses were rejected. WD had significantly lower torque angles than N for all alloys (p<0.01 in each instance). In N brackets, NT resulted in a significantly higher torque angle than SS and TMA (38.0±1.2 vs. 25.8±2.2 vs.33.9±2.2; p<0.01; respectively), while in WD brackets, SS resulted in a significantly lower torque angle than the other two arch-wire alloys (21.4±1.1 for SS vs. 26.0±1.7 for TMA or 26.0±0.7 for NT; p<0.01) and no difference was found between TMA and NT.
Conclusions: (1) Differences occurred in torque angles between WD and N brackets; and among the three arch-wire alloys. (2) The force rotated wires to a higher angle than desired for incisors. (3) Orthodontic biomechanics must be explored by scientific method.