Depending on the kind of person you are, you might benefit from just observing without asking a bunch of questions on your first day or so. When you get to understand the atmosphere a bit more, i would start with questions as he is performing procedures. if you have a good dentist, he will take the time to show you what he/she is doing in case you don't have a good angle. I know I spent most of my time standing up and leaning over to see, sometimes literally over his shoulder.
Anyhow, Just ask what comes to your head. One of the things that I thought about after shadowing at least 10 hours or so was about how he deals with long procedures, especially the mental aspect. say you have been working on a patient for 3-4 hours and you are just getting exhausted and you're not able to focus on the task at hand; what do you do? Do you finish the procedure even though you are mentally tired, or do you stop the procedure at a point where it will hold until tomorrow and finish it then? That's just an example. i was really interested in the mental side of things, not so much about learning how procedures are done. When I wanted answers to questions like 'what is this instrument,' i usually asked the assistants and they were more than happy to answer my questions.
be polite, almost to a fault. smile a lot, try to engage the patient if the atmosphere at the office warrants it. But, as I said, you might benefit from a couple days of mainly just watching until you get more comfortable.
