That's not surprising for UV-triggered photopolymers. A material that will go from a liquid to a solid with just a nudge from some UV light has to be quite reactive. Here's the Material Safety Data Sheet for one of Stratasys's "bio-compatible" materials.[1] That stuff has to be contained in a cartridge for safety reasons. Once fully cured, it's supposedly safe for dental devices. Here's Form 1's clear material.[2] Lower hazard ratings, but still hazardous.<p>If the curing reaction doesn't go to completion, some of the source material will remain, which is a problem. If further exposure to UV reduces toxicity, the 3D printing process isn't finishing the curing process.<p>ABS extruders should produce objects no more toxic than the raw ABS. ABS is rather neutral chemically. When heated, it may give off "irritating vapors", says the MSDS,[3] and its combustion products are toxic, but cold, it should be harmless.<p>[1] <a href="http://usglobalimages.stratasys.com/Main/Secure/MSDS/Dental%20and%20BIO-Compatible%20Materials/DOC-06135-Objet-MED610-Biocompatible-Clear-US.pdf?v=635508817295287425" rel="nofollow">http://usglobalimages.stratasys.com/Main/Secure/MSDS/Dental%...</a>
[2] <a href="https://www.cs.cmu.edu/afs/cs/academic/class/15294-s15/resources/CLEAR+MSDS+v10.pdf" rel="nofollow">https://www.cs.cmu.edu/afs/cs/academic/class/15294-s15/resou...</a>
[3] <a href="http://download.makerbot.com/filament/ABS_MSDS_MakerBot_Stratasys.pdf" rel="nofollow">http://download.makerbot.com/filament/ABS_MSDS_MakerBot_Stra...</a>