Tim Ferris mentions this in his book:
Call 30 minutes before they open or 30 minutes after they close. Get to the decision maker no matter what.
Another thing you can try is getting a list of new businesses from your Chamber of Commerce. Most new dentists don't start up with a secretary. They would also need the leads more than anyone.
I tried this local search stuff for my area, exact same strategy, but didn't have the patience to wait for rankings. I hope it goes a lot smoother for you.
Best of luck and let us know how it goes.