It's normal for the schools that do it. Their curriculums are geared towards that. I don't know that it's encouraged at others. You have to get approval to take it, and they might not allow you to if they don't think you're ready. For me, it wasn't just allowed, it was they expectation. They offered everything we needed to study (didn't have to purchase any study material unless you chose to), did some mock boards, and gave us 3 months off between first and second year to take it. The advantage? You're done with basic sciences with 3 years of mostly dental emphasis after that. Second year has pharmacology, but that's way more relevant to our field than some basic science stuff (not that basic sciences are a compete waste). You also aren't having to go back and review material from almost two years ago when you take boards. We don't touch pharm first year because it's not on the boards (part I). I'd have to count, but I think ~15-20% of schools do it. Some others allow it/expect it mid second year (not sure how much time (if any) you are given to study for it).
