How do mechanical responses at closing loop ends vary when loop position changes? A systematic analysis of vertical, T-, and L-loops

Abstract

Closing loops are used in orthodontics to apply forces on teeth and cause them to move in a desired direction. The objective of this study was to investigate the effect of loop geometry and position on loop properties. Using finite element analysis, loop response was simulated for three closing loop designs (vertical, T-, and L-loop) at thirteen loop positions. Loop length and height were 14 and 10-mm, respectively. Loop properties (horizontal load/deflection, vertical force, and moment-to-force ratio M/F) on both ends were measured at 100 and 200g force activation or when moving both ends 2-mm together. It was found that the pattern of changes in loop properties with loop position was similar for the vertical and T-loop. They reached their maximum M/F-ratios of 5.5 and 7.3, respectively, at the ends closest to 1/5 or 4/5 off-center loop positions. M/F-direction at an end changed when the loop was about 2/3 away (vertical loop) or 4/5 (T-loop). The L-loop behaved differently, reaching its maximum 8.7M/F-ratio (200g activation) when centered. M/F-direction only changed at the opposite end of the L-loop direction, and occurred when the loop was centered. This study showed that loop properties depended on loop shape, position and activation. The way properties changed with loop position depended on their designs. Clinicians should consider the specific characteristics of each loop configuration for desired tooth movements.