Teflon and it's relatives--so long as you don't expose them to enough heat to mess with the C-F bonds, they're probably safe. But Teflon only exists as a solid, it will decompose before melting, thus the problem becomes how to form it? You need a solvent--a solvent that dissolves that which is famous for being impervious. To date only one such solvent has ever been found: it's pretty close chemically but one bond doesn't have a F stuck on it so it will play nice with both Teflon (which is what most of the molecule looks like) and other things (the piece that isn't like Teflon.) Can you hope to recover all of the solvent from the finished product? No way. And that solvent will react in the body, it's not inert like the Teflon. Toxic down to the detection threshold.
They have played games, producing "different" solvents but they're all the same thing, the same reactive part connected to a chain of a different length that is fully fluorinated. The length of the inert chain doesn't change anything, the toxicity comes from the one reactive part.