Evaluation of the torque control of the maxillary incisors in lingual orthodontics during retraction – A finite element analysis

Aims

The aim of the study was to evaluate the horizontal and vertical forces for effective torque control of maxillary incisors during retraction in lingual technique using a 3-dimensional (3D) finite element method. These horizontal and vertical forces were analysed and compared.

Methods and materials

A 3D finite element model of the maxilla and maxillary incisors and molars was made. The maxillary incisors were subjected to horizontal retractive force and the vertical intrusive force was calculated such that the resultant of the horizontal and vertical forces passed through the centre of resistance of the maxillary incisors to maintain torque and simulate bodily retraction in labial and lingual mechanics.

Results

For equal magnitude of horizontal retractive force (100 g) the calculated vertical force vector (Fv) was 129 g and the resultant force was 163 g in labial mechanics, while in lingual mechanics, the vertical force vector was 222.66 g and the resultant force was 244 g.

Conclusion

In lingual orthodontics, it is more appropriate to reduce the magnitude of horizontal retractive force and keep the vertical intrusive force within biological limits, thus maintaining torque and achieve bodily retraction of incisors.