Orthodontic tooth movement analysed by the Finite Element Method.

The position of the instantaneous centre of rotation (ICR) of a maxillary central incisor has been calculated using the Finite Element Method. It is shown that the centre of rotation is insensitive to the elastic properties of the periodontal ligament when Poisson's ratio (v) is in the range 0-0.45. The position of the ICR is independent of load but dependent on the point of loading, becoming less apical as the loading position moves above the cervical margin. This dependence when used in conjunction with the clinical findings of Stephens, suggests an inverse linear relationship between the ICR and rate of retraction.