Colonization with mutans streptococci and lactobacilli and the caries experience of children after the age of five.

Some authors suggest that there is a "window of infectivity" for mutans streptococci (MS) at an early age, after which colonization is not likely to occur. Moreover, children with low or non-detectable levels of MS at an early age are at lower risk for caries. It was our aim to study caries experience and colonization with MS and lactobacilli in a group of children at 11 years of age who had been documented to have been MS-free until 5 years of age. For this group, the mfs and MFS values at 11 years of age were found to be 1.12+/-2.81 and 0.44+/-0.88, respectively. These values are much lower than those of a control group of 11-year-old children who had always been MS-positive since the age of 2, being 3.10+/-3.43 and 1.20+/-1.91, respectively. Of the 30 children without detectable MS up to the age of 5, 22 had acquired MS at 11 years of age, but their MS counts were significantly lower than those of the control group. No correlation was observed between the levels of MS of the children and the mothers. In children at 11 years of age, no differences were found in the numbers of lactobacilli and sugar intakes per week between the children MS-free and the children MS-colonized at 5 years of age. The present study indicates that the acquisition of MS is still possible after the so-called "window of infectivity" and that a delayed acquisition of MS may reduce the caries experience in the primary and permanent dentition at a later age.