| CPC A61C 7/08 (2013.01) | 22 Claims |

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1. An orthodontic appliance comprising:
a first shell adapted to receive patient teeth, wherein the first shell has a bottom first surface for engaging the teeth and a top second surface opposite the bottom first surface and a first edge defined therebetween;
a second shell shaped to be stacked over the first shell, wherein the second shell has a bottom second surface, a top second surface opposite the bottom second surface and a second edge defined therebetween; and
a first chamber defined between the top first surface of the first shell and the bottom second surface of the second shell, and a first perimeter seal formed between a portion of the top first surface of the first shell and the bottom second surface of the second shell; and
wherein the first chamber comprises at least one tack-free contact point between the first shell and the second shell within the first chamber, each contact point permitting movement between the first shell and the second shell.
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