Dentists have been saying this for years, but a recent Japanese study only confirms that there are subtle, but significant changes after even 2-3 years of CPAP use. The authors observed a reduction in the prominence of the upper and lower jaws. Not too unexpected, since constant pressure on the jaws can cause dental changes. Here's an article that references the paper.
After using a nasal mask for 6 - 8 months, I noticed my teeth start to shift. In particular, my two front teeth started to splay and separate slightly. I have switched to a full face mask and it doesn't cause as much pressure on my teeth.
Thanks for posting the article.