If you have the time/money/inclination, here's a tutorial on how to make safe SFX dental appliances:
There are also independent makers of SFX teeth appliances who would be able to make you custom re-useable appliances that are safe for your mouth.
tl;dr if it's not meant to be put in your mouth, you probably shouldn't do it. If it's not comfortable and doesn't allow you to talk clearly to other people, you're not going to end up wearing it very long, and then your time will be wasted and your costume detail missing. Remember those stupid one-size-fits-all vampire teeth in halloween stores? That you had to stick in your mouth like a retainer? You couldn't talk to people or comfortably close your mouth, and it was just stupid.