Yeah, a couple years back I had visited the school and they mentioned that they want you to shadow at least five different dentists. Its on their website as well. I thought this was much as well because I had worked as an assistant already for two dentists (they were husband and wife) between two offices, which I thought would be ample exposure. She then listed some names of dentists in town that I should ask. She told me that different dentists will run their offices differently...I went ahead and applied without the additional 3 dentists thinking that i would be ok, I still got the interview, but after the interview I got an email from the admissions coordinator saying I needed to get those additional dentists on my application. I got the other dentists to let me shadow for maybe 4 hours each, but the bulk of my exposure was from being an assistant. I would still check with the schools that you are applying to.