your not the first person to ask this question and so far I have found the best answer is from "warbow"
"Well, I'm all for pointless idle speculation and empirical testing! It sounds like fun to me. The only downsides being the possibility of breaking expensive ILF limbs and sever personal injury
The fact is that bow strings for 100 pound plus warbows used to be made out of **linen**, which is nowhere near as strong as nylon. Medieval archers would have killed for such a material (well, perhaps just roughed you up...) Anyway, a nylon bow string should be sturdier than linen, even if not ideal. But rather than just making a bow string out of dental floss, why not do some static breaking strength tests to compare the breaking strength of a single strand of dental floss to a single strand of B50, which has a static breaking strength of around 50# (is that where the B50 comes from?). Then you can calculate how many strands of dental floss you might need--assuming that the nylon in dental floss has a similar dynamic breaking strength as dacron (a pretty big assumption, but I'm guessing it should be true, and I think that nylon is actually more elastic than polyester, IIRC). I'm going to guess that the equivalent nylon string will be much thicker than even dacron, and certainly more so than 8125.
Oh, and try a static test on the teflon strands. Those should be pretty weak, and probably near useless as bowstrings. But, if you are stuck in the wilderness with nothing but cases of dental floss, a spoke shave and some hickory staves... (I'm not sure if minty snares would work...) "