student02,
Chances are that you'll need to build up a relationship with the dentist before he allows you to assist in any way (although this isn't always the case).
If you find yourself standing in a corner, then ask lots of questions. It you ask "what class of occlusion is that?" then he/she is bound to invite you over to the chair as they explain the carie, etc. to you.
Even moreso, people love to talk about themselves, so ask questions about the dentist! Find out where they went to school, what their class was like, how long they've practiced, information about their patient base, etc. Get up to speed on current events in dentistry and ask the dentist for their opinion on these topics. A simple question such as "How do you feel about the current state of orthodontics being practiced in the U.S.?" will often spark a 20-30 minute discussion.
I guess, above all, show the dentist that you are committed to the field (or want to truly find out if the field is the right one for you to be committed to!) and not just their to fulfill a requirement. I've built an awesome relationship with my dentist and he now lets me explain procedures to patients (to the best of my ability). He even tells them to ask me questions during procedures -- which I try to answer (and often times fail!). It's been a great experience for me, but your standing in the corner isn't going to cut it. It's certainly not your fault, but try to become more active when observing. Think of it as a class and ask as many questions as possible without being annoying. Good luck!
-G