Experiments with beagle dogs show that groups of teeth can be rearranged by orthodontic appliances, within a few days when bone is weakened by corticotomy. The rapid movement does not damage the vascular supply of the pulp. This is demonstrated by intravascular injections of Plastoid. If the marginal bone is not impinged upon by the ostoetomy saw, only vascular changes in the free gingival mucosa indicate slight reactions of the parodontal membrane.