The physical characteristics of neodymium iron boron magnets for tooth extrusion.

Impaction and non-eruption of teeth is a common problem encountered in orthodontics and many techniques have been proposed for the management of this condition. It has been advocated that a system utilizing magnets would supply a continuous, directionally sensitive, extrusive force, through closed mucosa and thus provide not only a physiological sound basis for successful treatment, but also reduce the need for patient compliance and appliance adjustment. This ex vivo investigation examined in detail the physical characteristics of neodymium iron boron magnets employed in attraction in order to assess their usefulness in the clinical situation. Attractive force and magnetic flux density measurements were recorded for nine sets of magnet pairs with differing morphologies. The effect of spatial relationship on force was assessed by varying vertical, transverse and horizontal positions of the magnets relative to each other, and by altering the pole face angles. The data obtained suggest that magnets with larger pole face areas and longer magnetic axes provide the best performance with respect to clinical usefulness. It was possible to formulate a specific relationship between force and flux density for each magnet pair. This relationship can be used in the clinical management of unerupted teeth to predict the force between the magnets by measuring the magnetic flux density present at mucosal level. The results indicate that magnetic systems may, indeed, have a place in the treatment of unerupted teeth.