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).