i couldn't agree more with sfpredent. there was nothing that remotely compared to my experience abroad.
as far as finishing the prereqs, i'm an engineering major, but still managed to finish the prereqs for d-school and miss 2 quarters of school for study abroad and i was fine. in fact, during study abroad, none of my classes even applied to my major or the prereqs, they were just breadth classes, art history. and i never took summer school either, and i still finished in 4 years...so it is MORE than possible.
in my opinion, most people don't take advantage of this great opportunity. when will you ever have the chance to live in another country for any extended period of time. man, i wish dental schools that more experiences like this.
in fact, i will go to the extent of saying that it would've been worth an extra year of school. you're only young once, enjoy your youth.
and like sfpredent said, it makes great discussion during interviews (although in no way was that the reason that i went abroad).
so definitely go abroad. and in my biased opinion, go to roma...you'll love it!