CT, what this answer really depends on is your GPA. If it is sub 3.0, you have a LOT of work to do. Likely this will involve 2 or more years of school. Since you didn't give a GPA and may not want to for personal reasons, here are my thoughts for what it is worth.
1. If your GPA is CLOSE to a 3.0, an MS is a good way to go. The GPA will be counted independent of your undergraduate GPA but then you will have a fall back degree if you don't get into dental school or while you are trying to. An MS with a GPA >3.5 will look good IF your DAT scores with this low uGPA are better than 21.
2. If your GPA is WELL below 3.0 and your ONLY goal is to get into dental school, I would personally take a LOT of post bacc courses because that counts as your undergrad GPA. You can raise it this way so you will be more competitive but you won't have the masters or additional research planning to hold onto.
The most important thing with sub par stats is to do VERY VERY well on your DAT... probably nothing less than a 21 will do unless your GPA is not truly as bad as you are making it out to be.
Just my thoughts. Good luck to you.