Patent ID: 7641828

Claim:
A method of making a removable dental positioning appliance, comprising: forming a sheet of a first transparent material into a shell having cavities shaped to receive and reposition teeth from a first orientation to a successive orientation, wherein the first transparent material is selected from the group consisting of styrenics, ion-containing polymers, polymeric laminates thereof and polymeric blends thereof; and applying a coating of a second transparent material onto the shell such that the shell has a tensile strength at yield of greater than 6,000 psi, an elongation at yield of greater than 4%, an elongation at break of greater than 80%, a tensile modulus greater than 200,000 psi, a flexural modulus greater than 200,000 psi, stress relaxation over time of not more than 50%, and a transmissivity of light between 400 nm and 800 nm greater than 75%.