The funding has to do with research grants. All it means is that Michigan has tons more research going on than UPenn. That's not hard to discern from the information the schools have provided. UPenn DOES have research, and good research I might add (I was reading some of the papers recently published), it's just that Michigan is more research intensive at the dental school and probably have more faculty and larger research departments. Michigan also has a formal combined degree program which means that they have a T32 grant. Those types of grants are HUGE because they fund students for the entirety of their dental education if they're concurrently pursuing a DDS with a PhD. If you look at the top schools with NIH funding most of them have formal combined DDS(DMD)/PhD programs so that also accounts for a huge portion of the money you're seeing displayed.
If you're REALLY interested in research Michigan may be a better bet but at this point the dental education at both schools is good.