For operative dentistry, start with The Art and Science of Operative Dentistry by Sturdevant. For dental materials, beats the heck out of me; let me know when you find a good one. For pharmacology, that's a fairly advanced topic and I'd look at biochem before delving into it. For oral pathology, a similar deal: I'd go to oral anatomy and histology first. I have no idea about Penn in particular. In general, go to half.com or ebay and get old editions of whatever books if you're not ready to drop a load of cash on this preliminary endeavor.
Some people may try to discourage you, but as long as you're not going around calling yourself a dentist (or a dental student) if you're not one (FYI I am neither), I don't see anything wrong with reading up on what interests you. In fact, studying (especially material we really like) makes some of us just plain happy, so I say go for it. Best of luck!