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My tongue is so big that it takes up the whole inside of my mouth. There is no place for it to go other than be parked on the roof, behind my upper front teeth. That being said, I could blow up a ballon with my tongue in that position. It does not stop pressurized air from blowing through. Now if only I could train myself to breathe when I'm sleeping!

Bev

I don't know if you might have seen my other post in a different topic, I have found that I don't need my mouth sealed shut. All I require is gentle pressure on my lips
to prevent the air from blowing out. I have been using a bandana, rolled over twice. I tie it off around the back of my head and the pressure is perfectly suited for this purpose.
Also, I think that it is a good solution because you can still breathe through the bandana material if your nose stuffs up. To me, it seems significantly safer than taping or gluing your mouth shut. I recommend at least trying it.

My chinstrap comes around my chin and covers my lips. Not enough pressure to keep the air from blowing out, but enough to help hold the tape on. My pressure goes up to 23 so maybe that's the difference?

I've been trying to train myself to keep my mouth closed. My husband thinks that's almost impossible, but he is hoping!

Some have been successful training themselves to sleep without mouthleaking. I'm one of those who gave up after the first six months. After I started using a full face, I never looked back. Many have had success with mouth taping, which is - in essence, equivalent to using a full face mask. (You're still supposed to try to breathe through your nose with a full face mask. It just makes it easier to keep the air column pressure equal between mouth and nose, so mouth leaking doesn't occur.)