If there is a significant cost difference, go to the cheaper school. I assume BU is far less expensive than Penn with comparable cost of living, but I don't know. If they cost the same, then Penn would be a good call. They're about to seriously upgrade their school (right now their clinic is absolutely archaic), but the reputation does precede itself, I guess. Point being: you can specialize out of any dental school; it's about the individual, not the institution. If you expect your school to do that work for you, then you're setting yourself up for failure. Even if you don't match straight out of BU, there is no guarantee you would out of Penn either. Further, you can always do a GPR, etc. or work as a GP and reapply. You will get in the second time around, most likely. Don't make a bad choice based on "prestige" and assumptions. You control your own destiny, not your school and ultimately you need to decide what is right for you. I turned down an Ivy and am still in a position to do whatever the heck I want b/c I'm at the top of my class, extended myself in multiple leadership capacities, done a good bit of research, externships/missions, and have developed good relationships with mentors/professors for future letters. I don't expect my school's name or prestige (or lack thereof) to do ANY of the work for me in applying for residencies. Neither should you.