I wore a plain black dress with black tights and black flats and a cardigan with a long necklace. Most people wore similar stuff and it doesn't really need to be super formal, just tidy and respectable because the interview is super quick and fairly casual (from my experience at least).
Questions I got last year:
Why do you want dent over med?
What do you think a dentist does in a day?
What qualities do you think a dentist needs?
What's a hard decision you've had to make before and how did you decide (thought processes)?
Why do you think research is important in dentistry?
What are some of the negative aspects of dentistry?
Then the scenario was something along the lines of ... you're fourth year dent but not sure that you really like it, what would you do?
Physio exactly the same but change dentist for physio!
Just try be genuinely nice and make sure you sound like a real person and not just a robot repeating your pre-learned answers
Good luck
