In vitro evaluation of loop design influencing the sliding of orthodontic wires: A preliminary study

Aim: Resistance to sliding between bracket and wire is present, in a different magnitude, in most orthodontic treatments and it affects the biomechanics of the tooth movement. However, the influence of loop design on resistance to sliding is currently unknown. Methods: In total, 12 stainless steel orthodontic wires of different sizes (0.016″×0.022″; 0.017″×0.025″), loop height (6mm, 8mm, 10mm), and loop type (open, close) were analyzed. Wires were tied with elastic ligatures to a bracket and tested during sliding at 0.5 mm/min. Straight wires were used as controls. Differences in the force to start the sliding (N), force during the sliding (N), and displacement to start the sliding (mm), were evaluated with Kruskal–Wallis one-way analysis of variance and Mann–Whitney tests (α=0.05). Results: Open loops had a lower force to start the sliding compared to straight wires (p<0.05), and some closed loops showed a similar trend. Open loops had lower force during the sliding compared to straight wires, but closed loops were less predictable. Displacement to start the sliding increased with loop height, and differences were present between loops and straight wires (p<0.001). Force to start the sliding and force during the sliding changed relative to loop type (p<0.05), and closed loops showed higher resistance to sliding. Differences were also found in force to start the sliding and force during the sliding between wire sizes, with larger wires associated with higher forces (p<0.05). Conclusions: Loops should be considered as significant variables in the resistance to sliding, as they can influence both the amount of force and the onset of sliding. Compared to straight wires, rectangular wires with open loops may help clinicians reduce resistance to sliding. Further studies are necessary to confirm these preliminary findings.