Wore a chinstrap for a few weeks, and then was able to go without it. Problem solved.
Then, a few months later I started mouth-leaking again. I had to start wearing the chinstrap again and it immediately fixed the problem. Weeks later, after wearing the chinstrap every night, I got up to get some water and forgot to put it back on. I woke up a few minutes later with air hissing out of my mouth.
So, I conclude that it is a training device, but it's not just a training device. Based on my experience, I have to agree with Archangle. The chinstrap provides enough force to keep the mouth closed when we fall asleep and relax the chin muscles.
Apnea Board Moderator