IMO, 20 shadowing hours should be enough. Dental schools don't want you to already be a dentist without even having attended their program. What they do want to see is well-rounded students with strong academics that have displayed an interest in dentistry as a career. Let's face it, some of the people you see with 1,000+ shadowing hours obviously work in dental offices. The majority of them were probably hired on as office assistants and occassionally stepped back and watched a procedure every now and then when they got a break from answering the phones or filing, and now they list every hour they ever spent in the dental office as "shadowing" hours. That's just BS and so unnecessary. Go shadow a dentist for 20 or so hours, ask questions, and enjoy the experience. No need to go overboard like many others do here. One thing though, keep up your grades. Grades will get you into dental school. 1000+ shadowing hours will not.