it seems nobody was trying to answer this simple question, so let me be the first person who answers your question.
Very Very competitive, and it's not easy to be a doctor(dentist).
Health related jobs got something to do with other people's body which can be directly related to their life. Doctors can save people but one mistake can kill them too, so it's not just an easy going job that people can just have for fun. They have to understand how serious this subject is and they also need serious attitude about it. That also include serious attitude towards studying and people around you. I think that's what seperates medical,dentistry fields from other kinds of jobs.