You should not use a FDM printed material in the mouth for any longer times due to the above stated reasons, so there is not a good answer to your question.
I know that Formlabs are working on releasing a set of resins for long-term certified 3d printed dentures (one for teeth and one for the gum) this fall, and i'll think that you should be able to use the teeth one for printing provisional crowns on a Form 2.
Edited by Guest
Another caveat about using FDM printers other than what has been mentioned is that although you may find food safe materials, there is no guarantee that there will be no contaminants in the system or build area. For making mold from? Yes, but not direct.
Having just had a crown put in as well as a temporary provisional, I have to say the established practice of using molds to make temporary crowns can't be beat with FDM. The molding process is very efficient, cheap and yields a high quality product. I wouldn't reinvent the wheel here.
Just thought about this: you can not use other people and patients as guinea pigs. But you can use your own body. So, if you really want to know what these materials do in an aggressieve environment like the mouth: print a bridge for yourself, and put that over a couple of your own teeth. Use a transparant colorless material, so you can see all the little voids inside. For best accuracy, print slow and cool, but that means less flow and thus bigger voids in the model. Keep it in your mouth for a couple of weeks, and then watch it change color as bacteria grow and eat into the model. PLA is likely to decompose due to the aggressive enzymes whose job is to break down food, and PLA being bio-degradable... Other materials will probably get brown soon and start to smell. Part of the game is: you are allowed to clean the outside of the model when you brush your teeth, but not the inside, since you wouldn't be able to do that on a real crown too. So, any accumulated dirt will stay there. This would be a nice little experiment, but I am not going to do it. 
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geert_2 545
I don't think it is a good idea to use FDM 3D-printed objects in the mouth for more than a couple of hours. They are not accurate enough, so they are likely to cause irritation. But above all: the layer lines and little holes in-between are going to cause bacteria-growth and infections.
However, maybe you could use a 3D-print as model to cast a crown from? Then you can sand, polish and seal the model prior to making the mould, so the cast does no longer have any layer lines or imperfectoins? Then of course you could use plain PLA, or whatever you like most, and print slow and at low temp.
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