They are two very different options. With being a dentist, you only have to worry about the person's teeth and gums. If you become a nurse, you are dealing with their emotional health as well as their physical health. If you want to help people, I think you might get more satisfaction from going into nursing.
Have you considered job shadowing at a dental office? Try to get an internship in a hospital to see if nursing is for you (or if you like working in a hospital). You could also find dentists and nurses to interview about their job.