You obviously need to ask your interviewer why you should pursue a career in dentistry... I mean, you know, it's really important that you know right? (*note the sarcasm*)
Haha, being serious, most of the time, interviewers would prefer to talk about themselves than hear the usual BS that dental applicants feed them all day long. I ask them about their interests, hobbies, field of research, the city, their hometown, etc. In my opinion, the less time an interviewer spends grilling you, the less chance you have of disappointing them. I'm being honest here.
Take my advice.