Dentures and mask leak

I have been using CPAP for 15 years plus, I no longer have any issues and use it without a second thought every night. But now my 76yo father has started on his CPAP journey and is really struggling.

His main issue is mouth leak, likely caused by his false teeth. Somethimes he leaves the dentures in sometimes just the upper plate and sometimes he leaves them out enturely. In any case he gets terrible mouth leak.

At the moment he is using a Fisher and Pykel nasal mask, though he also has a Resmed full face mask that he has tried.

The fundamental probem seems to be that his have isn't firm enough without teeth to support the mask seal. Even a chin strap is useless.

Any ideas that have worked for people with dentures? Preferably not wearing the dentures at all at night.

I think the problem he has with a full face mask is that the crease between the chin and the lower teeth doesn't exist so the mask rides up and leaks above the nose.

He may do better with a nasal pillow style mask like the Fisher & Paykel Brevida, or the ResMed AirFit P10. They fit more on the bottom of the nose and I don't think need any support from the teeth. Mouth leaks may still be a problem. A chin strap can help, and for me I have found that mouth taping works the best to stop air leaks from my mouth. Some accept it, and some do not. See this video.

Mouth Tape for a Better Sleep

Try the Knightsbridge Dual Band chin strap. It's the only one designed to actually work. The Knightsbridge lifts from below the jaw and has two bands (one elastic, one non-elastic), so it can be adjusted to actually work and be comfortable.

The cheap neoprene ones you find on Amazon wrap around the tip of the chin and push your jaw directly into your jaw joint, which is the least effective and most uncomfortable angle possible. (Technically speaking, the design is poor because the force provides almost zero "torque." You want the force 90 degrees from what the neoprene ones provide.) I.e., the cheap neoprene ones aren't actually designed to work.