Stability of magnetic versus mechanical palatal expansion.

Spatial stability following palatal expansion (PE) treatment was studied longitudinally on 8 Macaca fascicularis monkeys. The sample was divided into short-term and long-term groups. The four subjects in each group received: (1) an indirect screw (IS) PE appliance (F = 2035 g), (2) an indirect magnetic (IM) PE appliance (F = 258 g and 360 g), (3) a direct magnetic (DM) PE appliance (F = 258 g and 360 g) and (4) a sham appliance. The terms direct and indirect describe force transmission directly, via pinning to the palatal shelves or indirectly, via abutment teeth. Active treatment in the long-term group was followed by a 4 month retention phase and a 2 month relapse phase. The implant study indicated the transverse stability to be greatest in the skeletally borne appliance. Correspondingly, intercanine distance relapse was 53 per cent and 23 per cent for the IS and DM subjects, respectively. Intermolar expansion was significantly more stable than intercanine expansion due to selective activity of the circum-maxillary sutures (transverse suture) and root configuration. Sagittal advancement and vertical superior translation, which are controlled by selective activity of the premaxillary suture, were particularly apparent in the magnetic appliances with a low force PE regimen. Clinical implications suggest that the use of a low force PE regimen can be of substantial benefit in young skeletal Class III patients with transverse maxillary deficiency.