I did something similar to an MMI interview when I interviewed to be an RA, but the questions can be pretty random depending on who's asking. Some asked why I wanted to be an RA, some asked what fruit I would be and why, and some asked if I were part of a bicycle, what part would I be?
Not sure if dental schools will be just as random in their question-asking, but I think the point is to feel loose and sociable in any given situation. Pretend you're at a professional dinner with some friends, don't be too tense.