Ask about the following:
1) research opportunities available to students
2) clinical chair time (do you fight for chairs in clinics)
3) technological advances availabilty in clinics and pre-clincal courses (Dent-sims, lap-tops, digital x-rays)
4) diversity of classmates and students that they accept
5) community services, does the school reach out to the community
6) Upper classmen exposure, will you interact with D3s and D4s in clinic to assist them or shadow them
7) scholarships? Are there any?
Do not ask:
1) What is your placement for graduating seniors in specialties
2) What is your NBDE Part 1 average or rank amongst other dental schools
3) Why I should pick your school?
Just some questions right off the top of my head....good luck during your interviews! Remember, always smile!