I, too, didn't know bottle mouth was a possibility in exclusively breastfed
babies until I saw it with a client of mine about 10 years ago.  She kept
her baby at the breast pretty much all night and, without any other possible
etiology that anyone could find, the baby's teeth grew in basically rotted.
Baby needed extensive dental work from the very beginning - dentist had no
other explanation other than "bottle mouth."  Since then, I've been much
more cautious about it - at least warn that it might be a possibility when
baby spends hours at a time with milk in its mouth.  I must admit, though,
I've never seen or heard of any other cases.

Gretchen