I kept quite a few undergrad textbooks....gen chem, orgo, biochem, and physiology. (and a few other textbooks that are irrevelant to dentistry)
It's really up to you- you can always borrow from library or google things to elaborate whatever you don't understand from class. But if you do keep your textbooks, I would keep biochem, anatomy, and physiology. The rest you can sell back/keep you warm during the winter.