I used to know this dentist who had origianally wanted to be a medical doctor. The reason he quit medical school and went to orthodonist school is as follows:
As you well may know (or you may not) in the first couple years of medical school the school will usually round up all the bums, homeless, prostitutes, and other people who probably don't see a doctor very often and bring them before the medical students to be vaccinated or tested for what-have-you. One day my old dentist friend was giving shots to some of the afore-mentioned people and being an extremely strict Christian was feeling rather uncomfortable around the prostitutes. However, being a professional, he covered his embarassment quite well. The next lady-of-the-evening sat down and he began the routine questions, etc. He told her to give him her arm and she was going to feel a "small prick" (from the needle) at this point she reaches down and grabs his junk. She then replies, "Hmmm, it's not that small fella." He removed her hand, stuck the needle in, bandaged her arm and quit medical school the next day.
He's a good dentist, but he always leans his back end as far back as possible from his patient :)