Laura,
Lactoferrin interferes with the ability of bacteria to metabolize
carbohydrates.  What causes tooth decay is the release of acids by bacteria as
the by product of digestion of sugar in the mouth.  Supplemental iron
saturates lactoferrin, and makes it ineffective.  I think one of the reasons
for bottle mouth in bf kids is our craziness to provide iron drops and iron
fortified cereals, which knock out the lactoferrin.  Also, some kids have a
genetic predisposition to tooth decay.  The feeling is that bf kids who get
tooth decay get it IN SPITE OF breastfeeding, rather than because of bf.
Cleaning the child's mouth with cool water on gauze, and later with a
toothbruch with plain water, will decrease the availability of sugar for those
bugs to digest.
Catherine Watson Genna, IBCLC  and mother of 2 former night nursers who are
now 5 and 9 and have never had a cavity.