| CPC A61C 7/08 (2013.01) [A61C 13/34 (2013.01); B29C 51/002 (2013.01); A61C 2201/00 (2013.01); B29C 51/30 (2013.01); B29L 2031/753 (2013.01)] | 4 Claims |

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1. An orthodontic appliance comprising:
a shell shaped to receive and reposition teeth, wherein the shell comprises an interpenetrating polymer network (IPN) material formed from multiple cross-linked polymers,
wherein a plasticizing solvent is configured to leak out of the IPN material over 1-3 days so as to gradually strengthen and reduce flexibility of the shell of the orthodontic appliance over the 1-3 days.
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