Fluoride in dental plaque and its effects

Total plaque fluoride is in the range 5-10 mg/kg (ppm) on a wet-weight basis. The variability of literature data on plaque fluoride is partly ascribed to analytical problems, many assays being close to or below the concentration detection limit of the fluoride electrode. A change in classification of plaque fluoride compartments is necessary, since recent work indicates that there are two pools of plaque F: less than 5% of the total F is in plaque fluid as the free ion, and the large remaining portion of total plaque F is designated as bound F, with the total F being greater than 95% extractable by cold 0.5 mol/L perchloric acid. Sources of plaque fluoride include the diet, saliva, and crevicular fluid; enamel is unlikely to be a regular source for plaque F unless it is either coated daily with labile fluoride compounds, such as calcium fluoride, or released by demineralization. The location and nature of plaque bound F are not established, but the present evidence is consistent with an intracellular location. Bound F may be released by acids produced in plaque during sugar fermentation, but it is unlikely to reach ion concentrations high enough for sufficient time periods to exert significant inhibition of plaque acidogenesis. Epidemiological evidence showing correlations between pooled plaque F concentrations and caries prevalence in the plaque donors does not exclude the possibility of coincidental effects of water F on both caries and plaque F concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)