P/F systems for dental schools are heavenly! I have only heard great things about them. All Pass/Fail Schools that I have heard about are more laid back and collaborative (they don't feel competitive). The UofM isn't P/F, so you typically have a mix of people that are "gunners" and people that are collaborative. In the UofM, you should be able to find a group that will be more collaborative, especially if they know that you want to be a general dentist too. You will assist your D1 year (not very often). Your D2 year, in the springtime, you'll start to see 1-2 patients a month doing very general procedures or cleanings. In the UofM, you really don't start seeing patients until your D3 year (like most schools). And your D4 year, you will typically see 1-2 patients daily. They also have a mandatory outreach program for your D4 year for four-eight weeks (this is where you'll see the most amount of patients). I am not sure what the clinical side for UPENN looks like.
I have heard MANY horror stories of professors on the clinical side and sim-lab not being the friendliest to students in the UofM. Professors destroying wax-ups that students have spent hours working on. Making students feel like they aren't the smartest in the sim lab and students leaving the sim lab in tears. And professors grade things; differently, you could have the same exact prep, and one professor will say that it is perfect, and another professor giving you a failing grade. A few professors take pride in that they grade with high standards, which isn't a bad thing. I have also heard professors being very friendly and helpful too! You will kinda get the luck of the draw based on where your seat is.