This question serves two purposes. It allows you to elaborate or improve upon answers you wish you could have answered slightly differently. Asserting where you wished you had communicated more effectively speaks to your communication skills and confidence. The interviewer also wants to assess your emotional intelligence, which is a trait they state on their website that they look for and foster in their students and which they consider one highly valued trait of a dentist. Therefore, your self-awareness and ability to identify exactly how well you are performing speak to your emotional intelligence. Be humble and honest, and take advantage of this opportunity to revisit previous questions if needed.