Effect of archwire size and lever arm length on anterior and posterior teeth movement during en-masse retraction in personalized lingual orthodontics: A 3-dimensional finite element study.

Objective: To evaluate the biomechanical effect of anterior and posterior teeth in en-masse retraction in lingual orthodontics using varied archwire sizes and lever arm lengths.

Methods: A finite element model of lingual orthodontics for retracting maxillary anterior teeth was established. The archwire was designed into: Archwire 1: 0.016×0.022-inch stainless steel (SS) with 15° extra torque on central incisors, Archwire 2: 0.016×0.024-inch SS with 13° extra torque on anterior teeth, Archwire 3: 0.017×0.025-inch SS with laterally 0.016×0.024-inch, and Archwire 4: 0.018×0.025-inch SS with laterally 0.016×0.0225-inch. Moreover, the lever arm was set to 0mm, 2mm, 4mm, 6mm, 8mm, and 10mm. Initial displacements were calculated after applying 1.5N force from mini-implant to lever arms.

Results: In Archwire 1, increasing intrusion and labial tipping on central incisors and decreasing lingual tipping on lateral incisors and canines, as well as decreasing palatal tipping and distal inclination on posterior teeth were observed with lever arm length increase. In Archwire 2, with the lever arm length increase, incisors exhibited increasing labial tipping, while palatal inclination and intrusion of posterior teeth decreased. In Archwire 3 and 4, torque control ability of anterior teeth increased with longer lever arms, as well as decreasing extrusion was observed on central incisors. Posterior teeth moved buccally and distally.

Conclusions: Thick archwire without extra torque combined with longer lever arm are more conducive to en-masse retraction of central incisor. Moreover, extra torque on thinner archwire can also effectively control torque. Besides, additional torque and lever arm lengths affect the movement of posterior teeth.