Hi PatternJuggler,
I also grind (used to grind I hope) my teeth. I've been having lucid dreams for a week now (on purpose anyway) and the second thing I do when I realize I'm lucid is tell myself to relax my jaw, the first is to relax my back (many problems with it too). So I know that at least in my case it does not interfere what-so-ever. I am going to try that mantra, hopefully I won't have to wait till I'm lucid to relax my jaw. Thanks.