i had a cervical fusion in may so i still have both my hard collar and my soft..i dont know how those would keep my mouth shut, i do know that it is very uncomfortable sleeping in them...good luck i hope you find a solution :)

It might keep your jaw shut but won't keep your lips shut so air could still escape. And I gotta believe e4now that sleeping in one would be very uncomfortable!
You just have to either train yourself to keep your lips shut or you have to use a full face mask which truthfully isn't so bad once you get used to it.

the only way to keep lips sealed is to tape them
chinstraps cant stop mouth breathing thru slightly parted lips
eventually with taping, most of us learn to keep our lips shut and so no more taping needed

I tried a couple of strips of paper tape last night. They seem to work at least as well as a chin strap except that I can't take a sip of water with them on. They won't prevent some mouth leakage but they don't leave strap marks on my head in the morning.
Mitch

I was using a soft cervical collar for many months before my MMA and my escape from PAP. I also have IIH so I was using it to try to stabilize my neck position to prevent compression of the jugular veins. but it would also stabilize the neck to prevent airway collapse that would change the amount of PAP you need. it did keep my mouth closed and I did not need to use my chinstrap with this. but I STILL needed to use THREE pieces of tape to prevent mouth leak. because I also have IIH, ANY mouth leak at all was deadly to me and would ruin my day.

for taping mouth, roll lips inward so tape goes on skin above and below lips, double tape back at both ends to form tear off strips
as mentioned most of us eventually find the lips stay shut so taping is no longer needed