As someone who got their PhD and then did a year as post-doc in a high-impact periodontology lab, DO NOT underestimate the time and shear determination it takes to do a PhD. You're looking at about 50 hrs a week between experiments, literature searches, and writing if you want to publish in a journal that's not garbage. Additionally, most dental research journals are horrid, and I'm not trying to flex nuts or anything, it's just the truth.
Doing your PhD is nothing like undergrad research and one really needs a great deal of self discipline to finish on time since you're being trained as an independent researcher. Hell, sometimes it's just luck! I lost atleast 7 weeks one summer because there was a H. pylori outbreak at Charles River and they had to start my KO mouse line all over again. I even waited two months for one of my my gingivalis antibodies because our cell culture facility got a mycoplasma infection and killed everyones hybridomas.
Why do I mention this? Because some days you just want to say, "F*ck This!" and walk out of lab. Call me a masochist, but it's the love of research that kept getting me out of bed the very next day. If you don't truly LOVE research, doing a DDS/PhD is a very poor decision, regardless of how many loans you might have. The funding situation for academic research in this country is awful, and I believe the lowest in history (if you account for inflation). In my experience from talking with associate-professors, your pay is also tied to the amount of grant money you bring in.