A new method for qualitative and quantitative evaluation of tooth displacement under the application of orthodontic forces using magnetic sensors

The purpose of this study was to develop a new method for the quantitative and qualitative measurement of tooth displacement under load and to clarify the relationship between the force system acting on a tooth and a resultant movement. A combination of eight magnetic sensors and a magnet was employed to measure three-dimensional displacement. Two sets of sensors and a magnet were placed in front and at the back of a front tooth subjected to orthodontic forces. Magnets and sensors were fixed to the subject tooth and posterior teeth, respectively. Sensors detected displacements of two magnets extended from the subject tooth separately in real time. The tooth trajectories projected on the sagittal plane were studied. From displacements of two magnets, angle of tooth rotation, the position of center of rotation and the amount and direction of displacement of an arbitrary point on the tooth could be calculated with high accuracy. Also, the location of center of resistance could be determined. It was found that the center of rotation is moving substantially even with a small difference in the level of force application. Furthermore, a small amount of displacement of the center of resistance was observed with varying the force magnitude.