UCSF, UCLA and UMB have the program too. Harvard must have one too (pls confirm)
If you want to do research, my thought is to get the dds first then pursue the PhD. Reason being that the combined program usually takes you away from your class at D3 and place you in a research lab for 3 years. After you have finished your thesis, you go back to finish your clinical rotation for another two years. The major disadvantage of this style is that you lose two years of knowledge while in the clinic. Given how fast research is coming (for particular projects anyway), you may miss that golden opportunity.
Then another thing is the cost. Going into a combined program could prevent you to take too much loans, but I am certain that dentists can earn enough to pay for the loan.
Do it if you get "high" when you are discovering science.
I am not 100% certain that I will be a researcher all my life,
but I am sure that in my career, I will incorporate some sort of experiments.