Comparison of force loss due to friction of different wire sizes and materials in conventional and new self-ligating orthodontic brackets during simulated canine retraction.

Aims: The aim of this study was to compare force loss due to friction (Fr) during simulated canine retraction using different archwire dimensions and materials between conventional and new self-ligating brackets.

Methods: The tested brackets were (1) conventional brackets (Victory series, GAC twin and FLI twin), (2) self-ligating brackets (Damon-Q, FLI-SL, new/improved FLI-SL (I FLI-SL), SPEED, GAC innovation (R) and Ortho Classic) and (3) a low-friction bracket (Synergy). All brackets had a 0.022″ slot size. The tested archwires were stainless steel (0.018″; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″); nickel titanium (NiTi; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″) and titanium molybdenum alloy (TMA; 0.016″x0.022″; 0.017″x0.025″; 0.018″x0.025″ and 0.019″x0.025″). Canine retraction was experimentally simulated in a biomechanical set-up using a NiTi coil spring that delivered a force of 1 N. The simulated retraction path was up to 4 mm. Force loss due to friction was compared between groups using the Welch t‑test.

Results: Force loss due to friction increased with increasing archwire size. Also, TMA showed the highest and stainless steel the lowest force loss due to friction. FLI-SL brackets showed the lowest Fr (31%) and Ortho Classic showed the highest (67%).

Conclusions: Increasing wire size generally showed increasing force loss due to friction. FLI-SL brackets showed the lowest, while Ortho Classic showed the highest friction.