A method for generating and reusing digital setups for an orthodontic treatment path. The method receives a digital 3D model of teeth, optionally performs interproximal reduction on the model, and generates an initial treatment path with stages including an initial, final, and intermediate setups. The method divides the initial treatment path into initial steps of feasible motion of the teeth resulting in a final treatment path with setups corresponding with the initial steps. For a treatment redesign, the method computes new steps of feasible motion for only a portion of the initial treatment path and based upon the initial steps, and generates the final treatment path with new setups corresponding with the new steps. The setups can be used to make orthodontic appliances, such as clear tray aligners.