I have made teeth using the above YouTube video, for my brother's Soul cosplay. It took a while to get the wonderflex bases to stay in properly- we initially cut off too much wonderflex, so if you go with this, be careful how much you cut off! But the end result was excellent. I can link the pics to you later (can't seem to upload the pic I want...)
These were made with both a wonderflex base and wonderflex teeth- the fake nails I had were too transparent and behaved strangely when I attempted to flatten them. The teeth supposedly cut his tounge once, but there was no blood and he's kind of a sissy when it comes to pain. Regardless, I'll be smoothing them out more. We have not yet made the bottom teeth- I am expecting them to be more difficult as they have to match up with the top.
I think they turned out great, though, and they are non-toxic. I have also seen the teeth made very sucessfully out of Sculpey (search the forums here) but worried about whether it was safe or not. Wonderflex is more expensive, but we bought the full sheet so I can use it for other cosplays in the future.
There is one other youtube tutorial I looked at. It was a bobby pin bent to fit the shape of the cosplayer's gums, and shaped fake nails hot-glued onto it. That would probably only cost you a couple bucks, so you might want to look it up.