Just be honest about your decision to drop out of dental school. Explain to them why you changed your mind, and why you no longer have an interest in dentistry. Tell them what changed between the time you were applying and the time you entered dental school to when you dropped out. I am sure that the people who are you writing letters of recommendations for you are going to understand.
I would, however, try to shadow as many doctors as you can, and also, try to volunteer anywhere you get the chance while you are in the application process. I am sure that you have done volunteering before, but the most experiences that you can discuss at your interviews, the better (at least in my opinion). This way you will be prepared with plenty of personal experiences when they ask you "What makes you decide you want to be a doctor now, and how do you know you will not change your mind about medical school once you enter?". This way you will be prepared for anything that they may ask you. As long as you are honest and sincere, I don't think your interviewers will hold you dropping out of dental school against you. Good luck with the application process