Wasn't watching the game, just saw the horrifying slo-mo of it on Twitter. Holy sh**, how was that not a penalty?
Somebody with better link-fu than me can probably embed the tweet: https://twitter.com/nickveronica/status/913606481924231168
Edit: Not to belabor the awfulness of that video clip, but if you watch close, it looks like a tooth goes flying along with the mouth guard.