I have worn a custom mouthguard for a few decades. I don't use it with my APAP for the simple reason that I broke my front teeth on the one I had after owning it just a month. Yes, my bruxism is that bad.
I have also had jaw surgery to advance my lower jaw. This was not an apnea treatment and took place a few decades ago.
I refused to even consider wearing a chin strap as a leak mitigator. It would have jammed my jaws together, a really, really bad plan. I could easily have smashed teeth.
I had to switch to an FFM because I couldn't use a robust enough jaw-flop device to keep from mouth breathing. To me,
mouth breathing is a sign my jaw is relaxed and my teeth are not grinding. This is a positive, not a negative.
I should have switched to an FFM way sooner.....Mine is very comfortable and I'm not savaging my jaws. My mouth just does whatever it needs to do.
However, I did study pictures of FFMs (actually of every mask I looked at) to be sure I didn't have headgear that pressured my jaws. I wouldn't have anything that sat on the joint. I used the website of
Supplier #1 to help out with photos.
My mask (F10) is liberally bedecked with Pad-a-cheek padding (I like the cotton flannel). This also lightens up pressure in the jaw area. Besides, my mask get-up now looks like the second coming of flower power, hippie mismatch, and twinkly stars. I feel sure this is unique, and what's not to like about making the mask your own?
Questions:
Is your mouthguard on your upper or lower teeth or both? That might make a difference if you want to try a tongue trick to keep air from flying out of your mouth. Personally, my mouth is too small for this trick: my tongue is always in that position. Your mouthguard might make this impractical too.
Have you tried a cervical collar? This didn't work for me, since my mouth flew open anyway (resulting in discomfort and leakage), but it does work for a lot of people. But it also might give you TMJ.
If not an FFM, can you find a mask where the headgear comes in at a different angle?