Salivary-free fluoride ion concentration measured using a flow-injection analysis device and oral environment in 4–6-year-old children

Although fluoride (F) products are widely used for caries prevention, the safest and most effective modes of application, in particular for young children, remain to be elucidated. The limitations associated with the detection of ultra-low F ion concentrations are the major obstacles in accurately assessing the salivary F ion concentrations in children. This study aimed to measure accurate salivary-free F ion concentrations in children using a flow-injection analysis device and highlight the conditions or substances that influence changes in salivary content. Subjects were 4–6-year-old children, and we statistically compared the data involving the number of decayed, missing, or filled surfaces (dmfs), the levels of Mutans streptococci (MS) and Lactobacilli (LB) cariogenic bacteria, and oral hygiene habits. The information on the latter was obtained using a parent/guardian questionnaire. The average free F ion concentration measured was 0.421 ± 0.158 μmol/L (0.008 ± 0.003 ppm), which was considerably lower than that obtained in previous studies using the conventional F electrode method. No significantly different correlations were seen between salivary-free F ion concentrations and dmfs, MS and LB levels. With regard to salivary-free F ion concentrations and oral hygiene habits, only finishing brush of subjects’ teeth by guardians showed a significant difference. In summary, the frequency of brushing was shown to correlate with free F ion concentration in saliva of children. Further studies are needed to circumstantially evaluate some other substances in saliva and oral hygiene habits.