Three hundred and thirty-eight children (age range 3-5 years) were examined for the presence of mutans streptococci in their saliva. They were divided into four groups according to the prevalent species that were isolated: (1) Streptococcus mutans and Streptococcus sobrinus group (S. mutans > or = 10(3) CFU/ml and S. sobrinus > or = 10(3) CFU/ml); (2) S. mutans group (S. mutans > or = 10(3) CFU/ml but S. sobrinus < 10(3) CFU/ml); (3) S. sobrinus group (S. sobrinus > or = 10(3) CFU/ml but S. mutans < 10(3) CFU/ml), and (4) children with mutants streptococci absent or barely detectable (mutants streptococci < 10(3) CFU/ml). The previous caries experience was compared among the groups, as was the caries increment during a 6-month period after the bacterial examination. The subjects in the S. sobrinus group had both higher caries and higher decayed teeth and surface increments than the S. mutans group. The mean decayed smooth-surface increment (delta d-surface) for the S. sobrinus group was 2.6 and was significantly higher than 0.8 for the S. mutans group. For the subjects with delta d-surface > or = 4, the mean number of S. sobrinus in the saliva was 4.29 x 10(5) CFU/ml and was significantly higher than 0.32 x 10(5) CFU/ml for the subjects without delta d-surface. There was no significant difference in the mean number of S. mutants in saliva between the subjects with and without delta d-surface. The prevalence of S. sobrinus in saliva was more closely associated with future caries activity, especially with smooth-surface caries increment, than the prevalence of S. mutants.
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