I think shadowing is more important because this is where you learn what being a dentist is really about. Research teaches you nothing about the practice of dentistry. When I interview people I want to know if they understand what dentistry is like. Sure, everybody shadows...because you HAVE TO. It seems most people do research as well. I couldn't care less if an applicant has done research because I know in nearly all instances their research role was not substantial. Cleaning glassware, pipetting, or running gels doesn't tell me about a person's prospects or interest in contributing future research findings to the profession. On the other hand, if they were the primary investigator, designed the research proposal, determined the methods, and wrote the publication, I would be impressed. Not many undergrads are capable of doing this. So, to reiterate: shadowing is more important than research.