Electronic determination of centres of rotation produced by orthodontic force systems.

A strain gauge measurement device with low force clip gauges, for measurement of initial tooth displacement in two dimensions has been developed. An experimental model simulating a maxillary central incisor is loaded with different known and controlled force systems. The resulting tooth displacements are described by the position of the centre of rotation and the generated angle of rotation for the total tooth movement. The effect of a single force, a moment, and force-moment combinations producing different moment to force ratios were studied. From these results the required force system needed to produce tooth movements with different centres of rotation for a central incisor of average root length are calculated. Furthermore, the model allows us to measure the accuracy of the measuring device by comparing results to analytical and laser holographic data, obtained on similar models. Some preliminary measurements and results, using human autopsy material are presented.