E.R.
My dentist told me the same thing about my 18 month old son, at the time. I did not stop nursing him in bed. Dentists have, I think, a dim view of extended nursing. What I don't get is, breastmilk has antibacterial qualities, too. So why would it cause tooth decay?
I nursed my oldest in bed to sleep till he was weaned (not my choice) at 19 months. His teeth are perfect. No problems. His ped. thinks the dentist is full of it, that people's pH in their mouth is what it is... and that is why people get cavities. He says he brushes his own teeth constantly and always has cavities, but he knows people (like me) who have never had a cavity no matter how much or how little they brush.
Use the flouride, I guess.. but my ped told me since the teeth are going to come out anyway, just to brush and hope for the best. Hope this helps. I would NOT want my child sedated, either.