Most, if not all, would be happy to let you shadow. I wouldn't shadow more than 5-8 hours a week because shadowing, in the whole scheme of things, isn't all that imortant. But to be safe, I'd ask the dentist what he/she is comfortable with, in terms of times per week and hours. You do that for a month or two and bam, there's 40+ hrs. As far as asking goes, I would call ahead of time so that you can meet with the dentist when he/she is between patients. Then, meet him/her in person and ask formally(wear something nice). If they try to give you any crap about hipaa regs, tell them that all they have to do is ask the patient if it's ok that you observe and then their office becomes a temporary classroom. I hope this helps, good luck!