When entering any stage of your career, it is important to possess the self-awareness to identify your strengths and growth opportunities. Perform the necessary research required on yourself to exude that emotionally mature level of self-awareness going into the interview. Midwestern University's College of Dental Medicine states on their website that they invest in their students' development in school and beyond.
When choosing a weakness (growth opportunity), choose one that is not a core skill for your success as a dentistry student. Sharing this with them can help them help you on your career path for professional and self-growth. Be sure to have an action plan to improve upon this weakness.