Ionized and bound fluoride in resting and fermenting dental plaque and individual human caries experience

Abstract Individual plaque samples were collected before and after sucrose application in situ from 75 school-children aged 10–11 yr (mean 10.7 yr, SD ± 0.8) with caries experience ranging from 0 to 21 DMFS (mean 6.7, SD ± 5.0), who resided in a low fluoride area ( 0.26 parts 10 6 F in the water), received minimal dental care and had poor oral hygiene. The samples were weighed, extracted with approx. 2 vol (by weight) of water and centrifuged; H + and F − concentrations were determined in the supernatant and bound F in the sediment. The concentrations (wet weight) of H + , F − but not bound F in resting plaque (RP) were significantly lower than in fermenting plaque (FP). Only 2.8 per cent of the total F was ionized in RP and 8.4 per cent in FP. The F − concentration was directly related to the increase in H + concentration. DMFS was significantly correlated with H + concentration in FP, the increase in H + production on fermentation, the F − concentration in FP and to the bound-F concentration in RP and FP. The results suggest that ionization of F on fermentation leads to overall loss of plaque F, that low H + concentration in FP is associated with high total F content in RP and FP, whereas the opposite is true for high H + concentration in FP, and that the cariostatic action of plaque F is mediated through the bound-F fraction.