[[Streptococcus mutans Acquisition and Dental Caries Development in First-Born Children].]

OBJECTIVE: To evaluate the moment of streptococcus mutans (SM) acquisition, caries development and their associate variables along 23 months, in first-born children of low socioeconomic status families, starting at 7 months of age. METHOD: The sample was chosen based on highly SM-colonized mothers, including all members of 14 families living in the same houses. The study included 14 mothers, 14 fathers and 14 first-borns and 8 relatives (mostly grandparents). Initial clinical examinations and radiographs determined the caries indices and periodontal conditions of the adults. SM count in all adults was made in the first 2 visits. The children were examined for SM count, number of teeth and number of carious lesions, in 4 visits. RESULTS: SM prevalence was high in the adults, being absent in only one of the parents. SM was found in 1, 2, 3 and 10 children in the first, second, third and fourth visits. Dental caries was detected in only 3 children in the last visit (at 30 months), who presented significantly higher SM scores than the children without caries in the same visit. CONCLUSION: A low income social condition and mothers highly colonized by SM do not mean necessarily early SM colonization and high caries activity in children with oral homecare. Caries development is significantly associated with high SM scores in the children.