Ask about the program, what they offer, what makes them good, what you will be taught to do (endo, extractions, implants, invisalign), graduation requirements, how their grads perform when they are out of school, where their grads tend to go.
Nearly every applicant that comes in asks the same dumb questions, questions that can be answered with a 2 minute scan of the ADEA book or with just a little intuitive reasoning. Know that information before you meet the dean. If you are a worthy applicant, the dean will want to sell the school to you. Remember, it is the job of the dean and the dean's colleagues to make the educational experience at their school as good as it can be. He or she is likely proud of the institution and will enjoy telling you about it, especially if you ask different questions that show a little knowledge and insight.
If you have to ask an admission question, towards the end, you could ask if there is anything besides the obvious that the school looks for and/or if they have a formula for rating applicants and how each component is weighed.