Effects of a magnetic palatal expansion appliance with reactivation system: An animal experiment

Introduction: The purpose of this study was to evaluate the effects of a newly designed magnetic palatal expansion appliance with a reactivation system. Methods: A magnetic palatal expansion appliance was designed based on the repulsion forces of neodymium-iron-boron magnets combined with a reactivation system. Eighteen prepubertal male beagle dogs were assigned randomly to the magnetic expansion (ME) group, the mechanical screw expansion (SE) group, or the control group. Two pairs of nonmagnetic metal bone marker implants were inserted into palatal bone bilaterally 3 mm lateral to the midpalatal suture and in line with the first and fourth premolars, respectively, in each dog. The 6 animals in each group received (1) newly designed magnetic expanders, (2) jackscrew expanders, or (3) no expansion appliance. Expansion was stopped after 4 weeks when 6 mm of activation was achieved in the 2 treated groups. Three-dimensional evaluations of dental and skeletal effects were performed with cone-beam computed tomography. Histologic examinations were conducted using light microscopy to observe morphologic changes in the midpalatal suture after hematoxylin and eosin staining. Results: The absolute transversal changes of both treated groups before and after expansion were significantly greater than those in the control group in all parameters (P < 0.001). The differences of the distances of bilateral canines in the ME group were significantly greater than in the SE group (1.04 +/- 0.16 mm; P < 0.001); the differences of the distances between implants adjacent to the first premolars (0.77 +/- 0.06 mm; P < 0.001) and the distances between implants adjacent to the fourth premolars (0.37 +/- 0.06 mm; P < 0.001) in the SE group were significantly greater than in the ME group. Histologic observations of the palatal sutures in the ME and SE groups, when compared with the control group, showed widening of the sutures and many fibroblasts in an active, proliferative state. Counts of osteoblasts were increased in both expansion groups. Counts of osteoclasts were increased in the SE group. Conclusions: Both appliances expanded the maxilla effectively and induced processes of bone remodeling of the midpalatal sutures during expansion. The new magnetic palatal expansion appliances produced a smaller skeletal effect and a greater dental effect than did the mechanical screw palatal expansion appliances.