In my experience, it's best not to ask more than 2 or 3 questions to the interviewers due to time limitations, even if they ask if you have any more questions. You can say that the dental students answered many of your questions (they like to hear that), and actually take advantage of the dental students to ask as many questions to them as possible.
Also, keep in mind that some interviewers won't even ask if you have questions, in that case is not appropriate to ask them at all.