you should be able to use any sort of mouthguard as long as it protects you, and doesn't harm other players in the water (kind of like the snorkel rule - no hard ones with sharp edges). keep it flexible. it's not a professional sport - as much as we'd like it to be. the simpler, the better. there are a lot of players out there and they're all very different. dont' put everybody into the same box, put a lid on it, and suffocate everybody.