Do your research before complaining about the lack of desire to work in the underserved. What you will find once you do this research, is that there's a reason why some cities have no to few dentists: those cities can't support a dental clinic. There are too few patients within a reasonable surrounding distance to sustain a practice. In many high need cities, you WILL go broke.
What about a large city such as SF where it's saturated with hundreds of dentists? Why are there only ~ 40 private dentists that may accept new patients with Denti-Cal? SF is lucky to be blessed with 2 dental schools, and that they take referrals from all over the bay area.
In my hometown, patients with Denti-Cal have 5 private dentists to choose from, or be put on the waiting list for at least 3 months at the county clinic. I know there are many other cities that are not as lucky.
http://www.denti-cal.ca.gov/WSI/Bene.jsp?fname=ProvReferral