An application of magnet and magnetic sensor: measurement system for tooth movement

A system for measuring tooth displacement and rotation in the sagittal and frontal planes was designed and tested. Four small magnetic sensors were arranged at each corner of a rectangular on a plastic sheet. They were then placed in the mouth and fixed to the front teeth with a plastic splint. A powerful magnet made of a rare earth metal was fixed to the target tooth and placed at the center of the sensors. Movement of the magnet was detected by the four sensors as the tooth trajectory. This system was tested by measuring first molar movement in human subjects with a load generated by an orthodontic aid. The system was small enough to fit in a human oral cavity and did not interfere with the orthodontic aid. Although the high humidity and high temperature of the oral environment were not agreeable for the sensors, resolution was estimated at better than 3 mu m, including the effects of system drift. The advantage of this system is not only the two-dimensional measurement, but also the rotational measurement, in which a 0.05 degrees resolution was calculated.