Effect of a static magnetic field on orthodontic tooth movement in the rat

Orthodontic tooth movement may be enhanced by the application of a magnetic field. Bone remodelling necessary for othodontic tooth movement involves e lastic cells, which are tartrate-resistant acid phosphatase (TRAP) positive and which may also be regulated by growth hormone (GH) via its receptor (G HR). The aim of this study was to determine the effect of a static magnetic field (SMF) on orthodontic tooth movement in the rat. Thirty-two male Wist ar rats, 9 weeks old, were fitted with an orthodontic appliance directing a mesial force of 30 g on the left maxillary first molar. The appliance inco rporated a weight (NM) or a magnet (M). The animals were killed at 1, 3, 7, or 14 days post-appliance insertion, and the maxillae processed to paraffi in. Sagittal sections of the first molar were stained with haematoxylin and eosin (H&E), for TRAP activity or immunohistochemically for GHR. The perce ntage body weight loss/gain, magnetic flux density, tooth movement, width o f the periodontal ligament (PDL), length of root resorption lacunae, and hy alinized zone were measured. TRAP and GHR-positive cells along the alveolar bone, root surface, and in the PDL space were counted. The incorporation of a SMF (100-170 Gauss) into an orthodontic appliance di d not enhance tooth movement, nor greatly alter the histological appearance of the PDL during tooth movement. However significantly greater root resor ption (P = 0.016), increased width of the PDL (P= 0.017) and greater TRAP a ctivity (P= 0.001) were observed for group M at day 7 on the compression si de. At day 14 no differences were observed between the appliance groups.