Estimation of the location of center of resistance of the tooth subjected to the load by measuring two target points' displacements in three dimensions

The line of action of a force in relation to the center of resistance of a tooth is an important consideration in determining a set of force and moment acting on the tooth. If the relationship between them could be clarified experimentally, the type of tooth movement would be also estimated, and efficient tooth movements will be achieved through the minimum course without round-tripping of the tooth thereby. We have developed a system for real-time measurement of two target points' displacements in three dimensions and determined the location of center of resistance of a maxillary central incisor subjected to orthodontic forces in human subjects. As a result, the center of resistance was observed at a point 0.19 times the root length from the alveolar crest and found to be closer to the crown than the location determined from a theoretical consideration. It was suggested that the location of center of resistance depends not simply on the shape of the root but on anatomical morphology of the surrounding tissues such as periodontal ligament and alveolar bone.