What I have learned is that both med and dent have to know how to diagnose and use critical thinking skills.
I think as far as skills are concerned, if you are going to be a GP (MD), you don't have to know how to use your hands that well. If you are a GDP (DDS), you not only have to work well with the hand-eye coordination stuff, but you also have to work sometimes within 0.1 of a mm. Dentistry is much more precision based than medicine... unless you are talking surgery.
Oh, and spatial arrangement is important because you have to work about 1/3 of the time or more backwards due to the mirror (not quite as difficult as it sounds after you get the hang of it, but it takes a WHILE!!!)