In Australia, as elsewhere, there certainly is a school of thought amongst
the dental profession that prolonged breastfeeding is associated with dental
caries.  Both La Leche League and NMAA have published material dealing with
this issue, because it is in the popular dental literature handed out to
mothers.  I like LLLI's summing up of the question, when it says that some
breastfed babies have dental caries despite breastfeeding, not because of it.

Often in the case of a breastfed baby with rampant caries, there was an
episode with high temperature either in the mother during pregnancy or in
the baby early in life.

As for the definition of 'prolonged', it is hard to work out whether they
mean allowing the baby to stay on the breast for along time (especially at
night) or breastfeeding beyond one year of age.  I have seen both
suggestions made as being the cause of the problem.

The definitive study would be one that looked at a group of babies and
checked the incidence of rampamt cries against the method of feeding (which
needs to be clearly defined).  There was a relatively small Scandinavian
study that  did this and found no correlation between method of feeding and
dental caries.  Strangely, I have seen no reference to this in the dental
literature.

Philippa Thomson
Information Officer at the Lactation Resource Centre (writing as herself
from home)