I nursed DS1 until he was 3.5 and co-slept so there was definitely night-nursing. He just had his first dentist appt a few months ago and the dentist said he had "great looking, super healthy teeth" so apparently all those years of night nursing didn't do any harm :)
Also, it sounds like that Dr is letting her own personal feelings about extended BFing influence her professional views. Very unprofessional IMO. In addition, as I continued to BF DS1 I heard more and more stories from moms I knew who had extended nursed their kids too. I think more people do it than most people realize, but people are often so rude about it that moms keep their extended nursing to themselves.
Sounds like you are doing a great job mama :)