US Patent 7878804 Tracking teeth movement correction

A method for tracking teeth movement includes using a set of positioning appliances shaped to move teeth through a number of successive stages of arrangements of an expected teeth arrangement model where each stage corresponds to a particular positioning appliance, mapping a current teeth position based upon positions of a number of physical markers attached to a number of physical teeth, comparing the positions of the number of physical markers with a corresponding number of virtual markers positioned on a number of virtual teeth of a stage in the expected teeth arrangement model, determining whether midcourse correction is needed.