I've been told numerous times by faculty in my department, particularly the grad advisor, that professional schools don't like it when you don't complete your masters before matriculating. In some cases, schools have offered people acceptances contingent upon their completion of the masters.
The other problem is that you may have difficulty finding an advisor who would be willing to take you on as a grad student if he/she knows you are going to leave if you get accepted to dental school.
Here's what I did: I graduated last june, mulled over the option of an MS degree, both thesis and non-thesis, and decided the best thing would be to be a post-bacc. But because i had a good relationship with the faculty in the bio department, I was able to get permission to take graduate classes, TA labs, all that stuff. Basically I had all the privileges of a grad student, but none of the research and no official title of grad student. If I had not been accepted this year, i would have entered the masters program because I believe I could finish it up by next year, since I had already started work on it this year. I probably could have gotten special permission to transfer my credits from my post-bacc year to apply to the masters program, and I had a professor who was willing to be my advisor and had a project lined up for me and everything.
My advice is not to start a masters program unless you plan to finish it. if you want to stay academically busy, just to a post-bacc and take the classes you want.
