Friction between Archwires of Different Sizes, Cross-Section and Alloy and Brackets Ligated with Low-Friction or Conventional Ligatures

Objective: To test the null hypothesis that no statistically significant difference in frictional resistance is noted when round or rectangular archwires are used in conjunction with low-friction ligatures (small, medium, or large) or conventional ligatures. Materials and Methods: A total of 10 stainless steel brackets, a 0.022-in slot, and various orthodontic archwires, ligated with low-friction ligatures or conventional ligatures, were tested to compare frictional resistance. The archwires employed were 0.014-in and 0.016-in nickel titanium (NiTi), 0.018-in stainless steel (SS), 0.016 × 0.022-in NiTi, 0.016 × 0.022-in SS, 0.017 × 0.025-in titanium molybdenum alloy (TMA), 0.017 × 0.025-in NiTi, 0.017 × 0.025-in SS, 0.019 × 0.025-in SS, and 0.019 × 0.025-in NiTi. Each bracket/archwire combination was tested 10 times in the dry state at an ambient temperature of 34°C. Results: Low-friction ligatures with round archwires showed statistically significantly lower frictional resistance than did conventional ligatures. When coupled with 0.016 × 0.022-in NiTi and SS, no statistically significant difference was observed among the four groups. When coupled with 0.017 × 0.025-in archwires, low-friction ligatures showed statistically significantly greater frictional resistance than was seen with conventional ligatures. When coupled with 0.019 × 0.025-in NiTi, low-friction ligatures showed statistically significantly greater frictional resistance than did conventional ligatures, but no difference among the four groups was observed with the 0.019 × 0.025-in SS. No significant difference was assessed among low-friction ligatures of different sizes. Conclusion: Low-friction ligatures show lower friction when compared with conventional ligatures when coupled with round archwires, but not when coupled with rectangular ones.