Re: peoples attitude
I agree with everything said here, but I also know that sometimes it's hard to ignore people you work with. I'm assuming that the people in your office are aware of your situation. If that is the case, the way that dentist is treating you would be grounds for a serious complaint to Human Resources or the Office Manager, whichever is appropriate in that venue.
I think if it were me in your shoes, I would try talking to that dentist and explaining that your situation is very difficult and would appreciate not being given medical advice. You already have a doctor that cares for you and your MD and are doing the best you can. Ask her to stop with the comments and if she refuses, file a complaint with the appropriate people.
I'm not positive, but I'm guessing that her comments and behavior towards you violate ADA.