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