This happened to me when I first started using CPAP about 2 years ago. And since then, my teeth have moved dramatically. I think its because I "fight" the air and clench my jaw and push my tonque (unconsciously) against my upper teeth. I now have large gaps between my top teeth that were never there before.
I would often wake up gnashing my teeth and would often bite my tongue. Also often wake up very sore on both sides of my tongue from clamping my molars down on it in my sleep.
I now wear the Sleep Right Night Guard which helped alot.
From time to time my teeth still ache - its a feeling just like when I wore braces as a teenager.
I also was just diagnosed with periodontal disease and my dentist did say that cpap could have contributed to that.