Hi Marie
In a paper written for NMAA in 1994 entitled Medical Advantages of Breastfeeding,
it was stated that a bacteria called Strep mutans increases an infant's
susceptibility to caries. The organism is transmitted from mother to infant
soon after teeth erupt. These bacteria ferment sugars which form acids
which demineralise the teeth. Sucrose in the diet increases the ability of
this Strep to colonise teeth. Lactose, the main sugar in breastmilk, is
fermented by strep, but it is not thought that it is capable of promoting
colonisation to the extent that it will cause caries.
Several studies have described a low incidence of dental caries in children
who breastfed. Alaluusua et al 1990 looked at 444 5 year olds with a known
breastfeeding history, and were unable to demonstrate an increased colonisation
of strep mutans regardless of whether or not the children had been weaned
early or late.. Nor could any increased colonisation be demonstrated in
children who breastfed frequently and also at night. It has also been
suggested that under normal dietary conditions, milk may not be very
decay causing and may in fact be protective (Ripa 1988).

Alaluusua S et al 1990. Prevalence of caries and salivary levels of mutans
streptococci in 5-year old children in relation to duration of breastfeeding.
Scand J Dent Res, 98:193-6

Ripa LW. Nursing Caries: a comprehensive review 1988, Pediatric Dentistry
10(4): 268-282.

Rugg-Gunn AJ et al 1985, Effect of human milk on plaque pH in situ and
enamel dissolution in vitro compared with bovine milk, lactose and sucrose.
Caries Res 19: 327-334

Westover KM et al 1989, The relationship of breastfeeding to oral development
and dental concerns. ASDC J Dent Child March-April: 140-143.

Hope this helps :)

Fiona Coombes
Breastfeeding Counsellor, Nursing Mothers' Assn of Australia
Lactation Consultant, Family Physician
Perth Western Australia