Salivary mutans streptococci and lactobacilli in 9- and 13-year-old Italian schoolchildren and the relation to oral health

The prevalence and levels of mutans streptococci (MS) and lactobacilli (LB) in saliva and its possible correlation with dental caries and periodontal conditions was investigated in 473 Italian schoolchildren, 9 and 13 years of age. A clinical examination and sampling of stimulated whole saliva was carried out in the school and oral health was assessed as DMFT and CPITN using the WHO criteria. The saliva samples were frozen in liquid nitrogen and after thawing, cultivated on selective media. To test the influence of cryopreservation, fresh samples from 20 subjects were cultivated. Thirty-five percent of the children were caries-free with a mean DMFT of 1.9 at the age of 13. The majority exhibited healthy periodontal conditions. Salivary MS and LB were identified in 52% and 21% of the children, respectively. The prevalence of MS was higher among the 13-year-olds than the 9-year-olds while no such difference was found regarding LB. There was a statistically positive relationship (P < 0.01) between the levels of MS and LB and both were significantly correlated to caries (P < 0.01). The correlation coefficient of microbial recovery between frozen and unfrozen samples was 0.99. In conclusion, the data provided cross-sectional information of a clear positive relationship between selected micro-organisms in saliva and caries in 9- and 13-year-old children in spite of a relatively low prevalence of the disease. The findings are discussed in a risk selection perspective