Variables affecting salivary Streptococcus mutans counts in a cohort of 12-year-old subjects

Several factors such as toothbrushing, diet, acidogenic potential of the mutans streptococci strain and site of the carious lesion can modify the salivary Streptococcus mutans (Sm) counts. In the present investigation the effect of some behavioural, clinical and microbiological variables on Sm salivary counts was evaluated in a cohort of 12-year-olds.

Forty subjects were examined by two calibrated examiners (GC, AL). The number of surfaces either decayed occlusal, decayed smooth or filled and the number of bleeding sextants, (clinical index for oral hygiene) were reported. Saliva was collected using a tongue depressor and was plated onto mitis salivarius agar with bacitracin and 20% sucrose. The presumptive Sm colonies were counted and the concentrations were logarithmically transformed. One Sm strain per subject was identified and the cariogenic potential evaluated as the minimum pH value recorded, during 5 hrs of incubation in 5% sucrose solution. The children's parents or guardians completed a questionnaire concerning the frequency of toothbrushing, the consumption of sweet foods and soft drinks and at what age the children started brushing their teeth. The effect of the explanatory variables on Sm count logarithms was evaluated by stepwise multiple regression.

The regressors with significant additional explanatory power were cariogenic potential (b = -1.335, p = 0.00001, R2 increment = 0.312), decayed smooth surfaces (b = -0.456, p = 0.009, R2 increment = 0.114) and bleeding sextants (b = -0.113, p = 0.004, R2 increment = 0.062), whereas the power of filled surfaces was marginally significant (p = 0.08).

On the basis of these results, it is suggested that acidogenicity is not only a cariogenic factor, but also a factor promoting colonization of oral sites by Sm, especially in subjects with a high frequency of sugar consumption.