Biomechanical responses of tooth to orthodontic forces applied at the lingual bracket positions.

The present study was designed to investigate biomechanical responses of tooth to orthodontic forces applied at the lingual bracket positions. A three-dimensional finite element model of the upper central incisor was developed to analyze tooth displacements and stress distributions in the periodontal ligament. Lingual horizontal and apical vertical forces of 100 gf were applied at a point on the labial surface of the crown and at three different points on the lingual surface of the crown. Tooth displacements and stress distributions from the forces applied at the lingual points were compared with those from the labial force loading. The following results were obtained. 1. Lingual horizontal force produced almost similar patterns of tooth displacements and stress distributions, irrespective of labial and lingual application points of the orthodontic forces. 2. Apical vertical force applied at the lingual points produced more uniform tooth displacements and stress distributions than labial application of the force, although the force applied at the lingual point close to the cervix generated different patterns from those with the remaining lingual force loadings. The present results suggest an important role of the positional relation of force application points to the center of resistance. It is shown that lingual force application may produce more optimal tooth movement in terms of more uniform patterns of tooth displacements and subsequent stress distributions in the PDL.