Cariogenicity depends more on diet than the prevailing mutans streptococcal species

This review aims to compare the occurrence and distribution of mutans streptococci in Africa, Europe, and North America and in addition will try to offer explanations for existing relationships among salivary mutans streptococci counts, dietary patterns, and dental caries. The literature reveals that salivary mutans streptococci counts in child populations of the three continents are comparable. The distribution of mutans streptococci species, with a predominance of S. mutans followed by S. sobrinus, and the virtual absence of other mutans streptococci species are also comparable. Although it is widely believed that diet has an important effect on mutans streptococci counts, this review provides evidence that this does not hold true when variations in dietary patterns are moderate, as they normally are in real-life situations. Since the diets of the child populations in the three continents vary moderately, a strong dietary-induced effect on salivary mutans streptococci counts cannot be expected. The observed analogous salivary mutans streptococci counts in these child populations are thus 'not surprising' but are in accordance with the conceptual expectation. The differences in caries experience in children of the three continents cannot be explained by the prevailing mutans streptococci species but instead should be attributed to differences in the cariogenicity of the various diets. The fact that the cariogenicity of the diet determines the development of dental caries while hardly affecting the mutans streptococci counts explains the limited value of the latter as an indicator of dental caries. The reviewed literature shows that mutans streptococci are ubiquitous in children aged 7 years and older in Africa, Europe, and North America. Mutans streptococci should therefore be considered as belonging to the indigenous microflora of the human mouth.