A computer-implemented method of planning an orthodontic treatment, the method comprising: receiving an initial digital data set representing an initial arrangement of a patient's teeth; generating a plurality of intermediate arrangements for successively repositioning the patient's teeth from the initial arrangement towards a target arrangement; determining geometries for one or more primer appliances (311, 312) comprising a first plurality of teeth receiving cavities shaped to receive a first plurality of teeth of the patient that are to be repositioned and to prepare the first plurality of the patient's teeth for the repositioning from the initial arrangement towards the target arrangement and a second plurality of teeth receiving cavities shaped to receive a second plurality of teeth of the patient that are not to be repositioned, wherein the first plurality of teeth receiving cavities of the one or more primer appliances are each shaped to provide an amount of force or torque to the first plurality of teeth when the first plurality of teeth are in the initial arrangement and the second plurality of teeth receiving cavities are shaped to enhance an anchorage of the second plurality of teeth that are not intended to move; and determining geometries for a plurality of treatment appliances (322, 323, 327) comprising teeth receiving cavities shaped to successively reposition the first plurality of patient's teeth from the initial arrangement towards the target arrangement, wherein the teeth receiving cavities of the plurality of treatment appliances are each shaped according to a respective intermediate arrangement of the plurality of intermediate arrangements following the first intermediate arrangement, wherein the first plurality of teeth receiving cavities of the one or more primer appliances are each shaped to move the first plurality of patent's teeth at a first movement rate between stages, and wherein the first plurality of teeth receiving cavities of the plurality of treatment appliances are each shaped to move the first plurality of patient's teeth at a second movement rate between stages, the second movement rate being greater than the first movement rate. receiving an initial digital data set representing an initial arrangement of a patient's teeth; generating a plurality of intermediate arrangements for successively repositioning the patient's teeth from the initial arrangement towards a target arrangement; determining geometries for one or more primer appliances (311, 312) comprising a first plurality of teeth receiving cavities shaped to receive a first plurality of teeth of the patient that are to be repositioned and to prepare the first plurality of the patient's teeth for the repositioning from the initial arrangement towards the target arrangement and a second plurality of teeth receiving cavities shaped to receive a second plurality of teeth of the patient that are not to be repositioned, wherein the first plurality of teeth receiving cavities of the one or more primer appliances are each shaped to provide an amount of force or torque to the first plurality of teeth when the first plurality of teeth are in the initial arrangement and the second plurality of teeth receiving cavities are shaped to enhance an anchorage of the second plurality of teeth that are not intended to move; and determining geometries for a plurality of treatment appliances (322, 323, 327) comprising teeth receiving cavities shaped to successively reposition the first plurality of patient's teeth from the initial arrangement towards the target arrangement, wherein the teeth receiving cavities of the plurality of treatment appliances are each shaped according to a respective intermediate arrangement of the plurality of intermediate arrangements following the first intermediate arrangement, wherein the first plurality of teeth receiving cavities of the one or more primer appliances are each shaped to move the first plurality of patent's teeth at a first movement rate between stages, and wherein the first plurality of teeth receiving cavities of the plurality of treatment appliances are each shaped to move the first plurality of patient's teeth at a second movement rate between stages, the second movement rate being greater than the first movement rate.