Patent ID: 8235713

Claim:
A system for repositioning teeth from an initial tooth arrangement to a final tooth arrangement, said system comprising a plurality of incremental position adjustment appliances comprising shells having cavities shaped to receive and reposition teeth, which appliances are successively worn by a patient to move teeth from one arrangement to a successive arrangement, wherein at least one of the appliances is a multi-layer shell appliance shaped to receive only upper arch teeth or lower arch teeth of the patient, the multi-layer shell appliance comprising a first polymeric material having a molecular structure which provides a first elastic modulus and the same appliance further comprising a second polymeric material of a different type having a molecular structure which provides a second elastic modulus, and wherein at least one of the appliances comprises a shell having a different geometry than that of at least one other appliance in the system, and wherein at least two different appliances of the system have different elastic moduluses and hardnesses with respect to each other, and wherein the first elastic modulus and the second elastic modulus each have a stiffness sufficient to impart a tooth moving force when the multi-layer shell appliance is worn by the patient.