AbstractBackgroundCaries is a worldwide distributed oral disease of multifactorial nature, with Streptococcus mutans being the most commonly isolated bacterial agent. The glycosyltransferases of this bacterium would play an essential role in the aetiology and pathogenesis of caries.AimWe explored how the glucosyltransferase‐B (gtf‐B) gene variability of S. mutans from children in central Argentina correlated with their caries experience and how these strains were genetically related to those of other countries.DesignDental examinations were performed on 59 children; dmft and DMFT indexes were calculated. From stimulated saliva, S. mutans was grown and counted (CFU/mL). From bacterial DNA, the gtf‐B gene was amplified and sequenced. Alleles were identified and their genealogical relationships established. Clinical, microbiological, and genetic variables were correlated with caries experience. Our sequences were included in a matrix with those from 16 countries (n = 358); genealogical relationships among alleles were obtained. Population genetic analyses were performed for countries with >20 sequences.ResultsThe mean dmft + DMFT was 6.45. Twenty‐two gtf‐B alleles were identified here, which showed low genetic differentiation in the network. Caries experience was correlated with CFU/mL, but not with allele variation. Low differentiation was found among the 70 alleles recovered from the 358 sequences and among the countries analyzed.ConclusionIn this study, caries experience in children was correlated with the number of CFU/mL of S. mutans but not with the gtf‐B gene variability. Combined genetic analyses of worldwide strains support the theory that this bacterium experienced population expansions, probably associated with agriculture development and/or food industrialization.