Mouth breather

There are several Full Face Masks that have a part that goes under the chin. Like the one I use, Fischer and Paykill Forma Mask, or one I have tried, the Rudolph V2. If I open my mouth while sleeping, it will leak. Just guessing, if you tried a mask with the feature of a chin cup restraint, and added a sufficiently strong chin strap, I do not see how you would much open your mouth without a major effort.

What affects me is that even with a very tight chin strap, the air enters through the nose pillows than recirculates, blowing OUT of the mouth, not breathing in. Mine was blowing my lips apart, resulting in very painful dry mouth. i couldn't get a chin strap tight enough to keep it closed entirely.