Comparative study of effect of different lever arm positions and lengths on transverse and vertical bowing in lingual orthodontics - An FEM study

Summary Objective To assess the influence of changing the size and position of lever arm on transverse and vertical bowing effects during retraction in lingual biomechanics. Methods A three dimensional 3D finite element method was used to simulate en masse anterior teeth retraction using lingual appliance with sliding mechanics. Two groups were made, 1st group had lever arm mesial to canine while 2nd group had distal to canine. Each group had 4 subgroups with lever arm height varying from 0 mm to 12 mm. Displacements of the maxillary anterior teeth were noted in each group. Results As the Lever Arm Height (LAH) increased in group I, the vertical bowing effect reduced while the transverse bowing increased with respect to canines. In group II, both vertical and transverse bowing effects increased but transverse bowing was less as compared to group I. Conclusion Strategic location of the lever arm is required in different clinical situations during en-mass retraction, keeping in mind the location of Centre of Resistance (CRes) as well as the vertical and the transverse bowing effects.