Why don't companies directly 3D print dental aligners?

This might be an obvious answer for someone more experienced with using 3D printers, but for a novice as myself I'm not quite sure I understand the engineering behind it. As I understand, currently aligners are thermo/vacuumformed from 3D printed dental molds. Why don't dental labs skip the step of 3D printing the molds, and just print the aligners? My research said that typical aligners are between .5 and 1.0 millimeters thick, and a lot of the dental printers out there have resolutions of 25 to 100 microns. Is it that it would just be too few layers, and therefore too flimsy for the aligners? Thank you in advance!

It has been done that way, but I think Invisalign uses the indirect method for a couple of reasons. One is that the material that's approved by the FDA to use in your mouth is expensive stuff. It probably saves them a lot in material costs to use cheap non-approved filament for the printing, while the vacuum-forming process is quick, cheap and easy. The vacuum-formed product would also be more cohesive and less likely to come apart in the users' mouths, while lacking the lamination lines of FDM printing, that provide great places for bacteria to thrive and multiply. But you might enjoy this story: http://amosdudley.com/weblog/Ortho

Thanks for the reply. That makes a lot of sense! It sounds like the main issue is economics then, and the actual engineering behind it wouldn't be too much of a problem in the future, especially given the increased quality of prints being produced. I have read the Amos Dudley story, and he actually made his aligners the traditional way using a dental model and vacuum-forming.

If the FDA approved material get's cheap enough do you think dental labs and companies will make the switch to directly 3D printed aligners? I would think that even though you are removing the thermoforming machine/plastic discs from the equation you replace it with a need to have a post-UV curing machine. All other steps of the equation seem to stay the same; oral scanning > computer processing > printing (mold or aligner) > (thermoforming or UV curing the aligner) > cutting/buffing the aligners.

Envisiontec seems to be contemplating a move in that direction; they recently got a material for making dentures through the FDA's approval process that works with their machines: https://3dprintingindustry.com/news/...inting-117507/

The additive manufacturing process permits curvilinear designs that are too expensive or impossible to do by subtractive methods , it was integrated with the DefDist V5 lower receiver. Further advantage was taken of the nature of FDM polymer printing to make it possible for printers with small work envelopes to produce large items, i.e., the Charon was designed to be printed in sections and then assembled with solvent cement.

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