This study aimed at comparing S. mutans in pairs of children within fa
milies; both children used a sweetened nursing bottle beyond the dieta
ry need, while one child was affected with nursing bottle caries (NBC)
, the other not. Seven families were selected. The children of a pair
showed no dissimilarities as regards dietary habits. Mean patient-age
was 3.7 yrs, controls 5.7 yrs. Saliva and plaque were sampled for CFU-
counting and clonal (DNA) type-screening of S.mutans. The NBC-patients
harbored significantly more S. mutans than the controls (mean 5.8 CFU
/ml vs. 2.9 CFU/ml). While the controls were colonized with 2-5 clonal
types of S. mutans, in the patients only one type was observed. The r
esults were not consistent for NBC-risk assessment by CFU-counting. An
inverse relationship between the number of clonal S. mutans types and
NBC is suggested.