Optimization of unilateral molar rotation correction by a trans-palatal bar: a three-dimensional analysis using the finite element method

Objective: The main goal of this study was to optimize unilateral molar rotation correction by modifying a trans-palatal arch (TPA) design using the finite element method. Design: Three-dimensional analysis of different TPA designs was carried out using the finite element method. Setting: Department of Orthodontics, Tehran University of Medical Sciences, Iran. Material and methods: For this investigation, 13 three-dimensional finite element models were produced for different TPA designs without pre-activation bends. Each model contained a palatal bar and two tubes. Optimizing unilateral molar rotations was achieved by five separate different paths: incorporating U-loop(s), 'R' loop(s) or helix/helices, a reverse action of the helix/helices and adding a straight wire to the design. The mesial part of the left side tube was displaced 0.1, 0.25, 0.5 and 1 mm, successively towards the midline, simulating palatal bar tab engagement in a mesio-palatal rotated maxillary left molar. The mesio-distal force, moment and energy produced in the normal side (right) molar were recorded for each of the models. Results: Findings showed that in all designs, the associated mesializing force was lower than that seen in the traditional design and the moment showed an increasing pattern when compared with a simple palatal bar. Regarding energy levels, the same increasing pattern was observed in the designs between activations of 0.1 and 1.0 mm. Conclusion: According to our optimized system, the TPA design with the highest energy and moment, but the lowest mesializing force associated with derotating a maxillary molar tooth was a parallel wire II design (i.e. adding a straight wire).