I have been using a ResMed with nasal mask for about 40 days now. You did not say whether you use a chin strap or not, but FYI, I tightened the chin strap to try and keep my mouth closed better, and the increased pressure on one of my lower teeth loosened it enough to feel it move and see a little blood emerge. If you do not have a good bite or your jaw recedes, it is possible to irritate your teeth. If you have a good dentist, you might want to take your headgear in and let her/him look at what is happening with your jaw and teeth while you are geared up for the night.