The value of the centre of rotation in initial and longitudinal tooth and bone displacement.

Force application on teeth and bone structures results in orthodontic and orthopaedic movements. The effect of force application during different time intervals (initial and longitudinal displacements) can be evaluated by describing the displacement vectors or by constructing the centres of rotation of the displacements. The aim of this investigation was to review different experimental studies to compare the position of the centre of rotation (CR) with the displacement vectors of the object (tooth or bone) after force application. The results indicate that the measuring procedure and the use of the CR to describe the displacement are very sensitive: a large discrepancy in the position of the CR does not necessarily lead to a major change in the displacement vector of the object. Displacement vectors seem to be more appropriate in describing both initial and longitudinal tooth or bone displacements.