Make a letter and express your desire to become a Dental Assistant or Front desk Receptionist, & also state that you are willing to volunteer for a few months. Remember that you are competing with a lot of experienced people in this field, so you have to be willing to start from the ground up to get your experience. I have seen many women, volunteer, Job shadow in the Dental Field and move along with their experience.
If you are very personable, quick leaner, then why not?
Voluntering would be the key, You may not get paid, but you are getting free training. Many Doctors do not mind, since wages are not arranged, only your time. It is a good opportunity to network with the Staff & Doctors. The Doctor could like you enough after some time, and hire you. Or a co-worker can tell you about a job opening and give you good word.