My sister is studying to be a dental hygenist, and to be accepted to the school, she had to take some biology classes at the community college, fill out an application, write an essay, and have an interview. She was accepted without much of a problem because she's been working as a dental assistant for the past five years at the same dentist's office, and is also X-ray certified; so she has lots of knowledge and experience.
One think you should be aware of is that male dentists tend to have an overinflated ego and act like jerks to their employees. I'm sure there are male dentists out there that aren't this way, but my sister hasn't met a nice one yet, and she's met a lot of dentists.