Evaluation of the Interaction Force of Nd-Fe-B Permanent Magnets Used in Orthodontic Devices

The use of devices with magnets for the correction of different malocclusions is an alternative to orthodontic treatment of teenagers and adults. In this case, tooth brushing is greatly facilitated due to the simplification of the apparatus design, which reduces the number of retention points for food residues. The number of patient visits to the doctor decreases and treatment time is reduced too. Devices with magnets have the following advantages over bracket systems: mechanics of force transfer without friction; predictable magnitude of the acting force; not required usage of maxillary elastics. The purpose of the study was to create a device for experimental measurement of interaction forces of Nd-Fe-B magnets of various sizes, the development of a methodology for the theoretical calculation of such forces, and comparison of the experimental and theoretical estimates. Material and methods. In the study we used Nd-Fe-B permanent magnets in the form of cuboids of various sizes. The force measurements were carried out using the specially assembled device based on analytical weights. The magnitude of interaction force between magnets was determined at separation of two magnets in the attracting configuration. Additionally, the magnitudes of magnets interaction force were calculated using the derived mathematical model. Results and discussion. We made up the device for experimental measurement of interaction forces of Nd-Fe-B magnets and carried out the measurement of the magnetic interaction forces for magnets of different sizes. For this purpose we proposed a method of theoretical calculations of the interaction forces between the magnets depending on the distance between them. We compared the magnetic force estimates measured experimentally and calculated. The influence of the opposite faces of the magnets was discussed. Conclusions. Estimation of the interaction forces between Nd-Fe-B magnets showed that modern materials science technologies made it possible to produce magnets of the required sizes comparable to the sizes of braces systems locks, providing the necessary forces for various movements of the teeth during occlusion correction. For experimental determination of such forces magnitude the device was assembled that allowed obtaining calibration curves for magnets of various sizes. The proposed theoretical method of calculation the interaction forces between the magnets showed a good correlation (not worse than 15%) with experimental data, which allowed designing orthodontic systems without additional experimental studies.