LLLI has some articles on nursing and dental caries on their website:

http://www.lalecheleague.org/bfdent.html

To the best of my recollection, the newest research indicates that
breast milk *alone* does not contribute to dental caries, even during
night nursing. But if the baby/toddler's teeth haven't been brushed
before bedtime, the combination of breastmilk and food is corrosive to
the teeth.

I have a good friend who is dealing with this right now. Her child has
weak enamel. Her solution has been to be scrupulous about the before-bed
teeth brushing. Her child's teeth seem to have stabilized.

Good luck!

Andrea Damon
LLLL Santa Cruz, CA

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