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The article says the braces are 2 layers. The inner one is polyester and the outer one is polyurethane. They also don't currently 3d print the braces themselves but instead thermo form them on top of 3d printed molds.

It has been done before.. https://www.businessinsider.com/how-to-3d-print-plastic-brac...

I wouldn't recommend it, mainly incase you mess up the teeth pressure and end up with a far higher dentist bill.

I think you'd end up with more plastic from just breathing in air and eating seafood than Invisalign, but I haven't done a study on that.