Guess I would have to ask myself...."what is it I am trying to hide" from my new doctor....and why?
What meds do you take? Do you abuse your meds, run out early? Ask for early refills? Did you old doctor actually dismiss you for the practice? What did the dismissal letter cite as a reason? Some more info would be helpful.
As for confidentiality, the new doctor will request your entire record, (as they should so they can properly treat you), so anything your doctor may have noted in your chart will be present in your record. You had to sign a consent to release your medical records to your new doc, so you essentially gave them permission to share the records with the new office.
What exactly are you afraid of the new doctor seeing? I'm guessing since you posted your question in an addiction forum, you're concerned about getting your medications? Pain pills perhaps?