Development of a magnetic sensing device for tooth displacement under orthodontic forces

We have developed a system for measuring tooth displacement from orthodonti c force. Eight small magnetic sensors and a magnet are combined to measure three-dimensional displacement. Sensors, arranged cubically in the three pl anes of space, are placed in the mouth and fixed to the posterior teeth by a splint. A magnet is placed in the center of the eight sensors and attache d to a front tooth that is subjected to orthodontic force, Sensors detect t he magnet's movement as target tooth displacement, The system was designed to achieve displacement resolution of 1 mum. The mean percentage of measure ment errors was determined to be less than 1% in a 600-cubic-mum volume fro m calibration. The system was tested clinically on human teeth. Although th e oral environment, with high temperature and humidity, was not agreeable w ith the sensors, this system was stable and accurate enough for quantitativ e measurement of tooth displacement. The advantage of this system is the ability to detect tooth trajectories by decomposing displacement into translation and rotation and to determine th e position of the center of rotation from these parameters.