To be honest, I would guess that the difference in AHI between 9 and 14 is not great enough to consider your therapy a success. I would also guess that if you had a dozen similar studies, they would fall roughly in that range. Not breathing 9 times per hour isn't good in any case. What was your blood oxygen level during these AHI episodes? I don't nor have I ever slept on my stomach but I used ONLY sleep on my side. First mask I had didn't allow for any position other than back sleeping. I found it most comfortable to sleep slightly propped up otherwise my lower back ached in the AM. I got used to back sleeping and now that I have changed mask types and can sleep on my side if I like, I still don't; still sleep on my back. PAP therapy puts CONSTANT air pressure on your airway and keeps it open enough where you won't cease breathing cycles (in theory)... not sure if this answered your question and not sure position of sleep is a key to effectiveness but know that stomach sleeping doesn't work for most PAP patients due the mask hose being in conflict with the pillow. Most sleep places sell special sleep pillows and the staff may be able to shed light on their effectiveness in your particular case. Sleep pillows come in a huge variety of conformations.
Wiredgeorge is correct in that a decrease in AHI from 14 to 9 is not a success. However, I have watched several people sleep flat on their stomachs while wearing CPAP, with their face and mask buried straight into the pillow. Apparently it works for them.
CPAP opens your airway and keeps it open - that's the whole point. The correct pressure is one that doesn't allow you airway to collapse, so that your breathing is uninterrupted.
Oh, and I've heard of many different pillows which people use.
Ok I can see some people here aren't supportive of oral devices at all as this discussion keeps talking about pap machines as if I should forget about the oral device and just move on to the machine. I didn't say 14 to 9 was a success. But it is an improvement, no? If the oral device wasn't working at all then I think my sleep dentist would've recommended that I move on to the machine instead of advancing the oral device again. Perhaps I should move this discussion to the "Problems you're having with your oral device" thread even though I'm not having problems with it because people in that thread appear to be more supportive about the oral device treatment. Oral devices aren't that bad and they have helped a lot of people with mild and moderate sleep apnea. My sleep apnea is more mild than it used to be now because of the oral device and that the sleep dentist has advanced it only a couple of times or in other words, only by a couple of millimeters.
And I'm sorry but the responses so far didn't really answer my question about the chin touching the chest issue. They just made it sound like I have to use the machine and forget about the device even though there's been some improvement.
Soft cervical collar, available in different sizes from Amazon, also I use a My Cpap Fit buckwheat filled pillow, also from Amazon, comes over stuffed and you can adjust for comfort. The collar will keep your chin from touching your chest and the pillow can be adjusted to cradle your head/neck to keep things comfortable. I used both of these with my xpap but have trained myself well enough to not need the collar now, I have come to really like the pillow and even travel with it.
The collar was under $10.00 but the pillow was more like $50.00.
As in all things YMMV, what works for me may be useless to you.