W.M. Edgar

The distribution and metabolic effects of human plaque fluorine

Abstract It has been shown by the fluoride electrode, by the liver esterase and colorimetric methods and by dialysis, that only about 2–3 per cent of the total fluorine of plaque detectable by chemical methods is present as free ions. There was no evidence of fluoride binding by plaque matrix or that the fluorine was present as insoluble inorganic salts. Plaque bacteria cultured on media containing fluoride contained high concentrations of fluorine and showed less capacity for acid production than controls, suggesting that the stored fluorine was active as an inhibitor. It is concluded that a high proportion of plaque fluorine is contained within the bacteria. Acid production was measured in vitro in plaque from children from towns with 0, 1.0 and 1.8 ppm F in the water. The results showed a smaller pH fall in the plaque from the fluoride areas which was highly significant with 1.8 ppm and of borderline significance with 1 ppm. It is likely that acid production was affected directly by the higher fluorine of the plaque but the possible indirect effect of lower caries incidence in the fluoride areas on plaque metabolism cannot be disregarded.

Uptake of fluoride and its inhibitory effects in oral microorganisms in culture

Abstract Fluoride (F) taken up by certain oral bacterial cells grown as pure or mixed cultures on F-containing media was present in two forms distinguished by acid-extractability. The F taken up inhibited the fall in pH when the cells were subsequently incubated in a buffer-glucose solution, especially if glucose was not added to the growth medium. Cells of Streptococcus sanguis H7PR3 suspended in F-containing buffer took up F which was readily extracted with dilute acid and was non-inhibitory. Cells of Streptococcus mutans FA1 did not take up F from buffers, but in separate tests were inhibited by external F to a similar extent to cells which took up F, suggesting that F-permeation of the cells is not essential for its inhibitory effect on this organism. Increased permeability to F at lower pH values has been suggested as an explanation of the greater sensitivity of bacteria to F at pH 5–5.5 compared with neutrality. This hypothesis was not supported by testing glucose utilization at pH 7 by cells pre-treated with F at pH 5–5.5. The increased sensitivity of bacteria to F at low pH was not explained by an effect of pH on F inhibition of enolase which is believed to be the inhibitory site of F in cells. The results suggest that both uptake of F into cells and their susceptibility to F inhibition vary with their metabolic state.

The effect of frequent sucrose mouthrinsing on the induction in vivo of caries-like changes in human dental enamel

Abstract In confirmation of the work of Fehr et al. (1970), optical changes in enamel resembling early caries occurred when subjects did not clean their teeth for 14 days and rinsed their mouths 9 times daily with sucrose solution; controls not rinsing with sucrose showed significantly fewer enamel changes. Subject-to-subject variations in susceptibility to the experimental challenge indicate a possible role for studies of this type in examining relationships between environmental factors and caries initiation.

Photographic and direct visual recording of experimental caries-like changes in human dental enamel

Abstract Changes resembling early caries were induced in human subjects by mouthrinsing with sucrose solution while not toothbrushing. The appearances induced could be validly assessed according to a graded index (Caries Index) and with a high degree of repeatability and reliability by the use of controlled colour photographic technique, but not with black and white photographs. The use of photography reduced possible bias inherent in the direct microscopic observations used previously. The grades of the Caries Index were related to graded appearances visible to the naked eye on the dry tooth surfaces with good illumination. Changes in the enamel surface occurred more frequently when the surface was covered with thick plaque than when little or no plaque was detectable.

Changes in the concentrations of phosphates in human plaque after the ingestion of sugar with and without added phosphates

Abstract The effect of ingesting sugar, with or without various phosphate supplements, on the phosphate concentration of plaque was investigated. Sugar containing 0.37 per cent of inorganic phosphate ( P i) did not consistently raise the Pi of plaque unless the initial plaque Pi was unusually low. This finding could be explained because the saliva stimulated by the sugar diluted the Pi so that its concentration was usually lower than that already present in the plaque. Sugar containing 1 per cent of certain organic phosphates which have been suggested as caries inhibitors did not invariably raise the total P of preformed plaque, but small increases in total P occurred when the sugar containing the phosphate was taken hourly during the development of the plaque. These variable and inconsistent results may explain why Pi supplements have usually been unsuccessful in reducing caries in man.

Clinical Science The Effect of Altering the Position of a Sugary Food in a Meal Upon Plaque pH in Human Subjects

Plaque pH in six adult subjects was monitored while they consumed a meal containing three foods. The marked fall in plaque pH caused by drinking sugared coffee was considerably reduced by eating the two non-sugary foods (egg and crisp-bread) before, during, or after the sugared coffee. This favorable action was negated by a pause between the sugary and non-sugary courses.Received for publication March 20, 1980 Accepted for publication July 30, 1980Plaque pH in six adult subjects was monitored while they consumed a meal containing three foods. The marked fall in plaque pH caused by drinking sugared coffee was considerably reduced by eating the two non-sugary foods (egg and crisp-bread) before, during, or after the sugared coffee. This favorable action was negated by a pause between the sugary and non-sugary courses.

Correlations between fluoride concentration, sample weight and acid production in dental plaque from children

Plaque was collected from 60 children aged 7 yr who were participating in a short-term study on the effect of fluoridized milk on plaque F. Plaque F was unaffected by 1 or 5 parts106 F in milk. Correlations and partial correlations were calculated between: plaque weight, plaque F and the initial and final pH of plaque/sugar incubations. The mean (±SD) plaque weight was 10.1 mg (±4.83) and plaque F (wet weight) was 3.5 parts106 (±1.79). Plaque F was significantly correlated with final pH (r = +0.42; p < 0.01) but the correlation was of border-line significance (r = +0.23; p = 0.06) when data were standardized on weight. Plaque F and weight were significantly correlated (r = −0.33; p < 0.05). The correlation between weight and final pH (r = −0.64; p < 0.01) was little affected by standardizing the data on initial pH or plaque F. The results indicate the importance of considering the weight of plaque when comparing F concentration or pH changes in plaque. The findings do not cast doubt on the validity of earlier results suggesting that pH falls were smaller in plaques from high fluoride areas because there is no evidence that fluoridated water reduced plaque weight.

Local Effect of Therapeutic Agents on Plaque Composition

Recently, interest has developed in the therapeutic use of substances with a local effect on dental plaque as a potential method for reducing dental caries.1-3 Various phosphates have been shown to reduce caries in animals, whereas the results of several clinical trials on the addition of phosphates in diets fed to human subjects have been equivocal.4 The mechanism of action of dietary phosphate supplements is probably a local effect on plaque composition since their caries-reducing effect in animals is not apparent after feeding by intubation.5-8 However, the clinical trials have not produced direct evidence that the consumed phosphate entered the plaque or significantly increased the plaque phosphate level for an appreciable time. Luoma, Hurskainen, and Isokangas9 demonstrated that a combination of sodium carbonate and sodium dihydrogen phosphate added to sugar at a level of 5% could raise the plaque inorganic phosphate content in 17 subjects with profuse plaque formation. However, in a group of nine subjects with less plaque, a rise in plaque phosphate content was not demonstrable. The absence of evidence concerning the effect on plaque of phosphate at the levels used as dietary additions in clinical trials led to the present studies on the local effect of various phosphates on plaque composition. Part of this work has been briefly reported in abstract form.10

Effects of calcium glycerophosphate and sodium fluoride on the induction in vivo of caries-like changes in human dental enamel

Abstract Optical changes interpreted as demineralization on the enamel surfaces of 8 volunteers who did not clean their teeth for 18 days, while rinsing 9 times each day with 50 per cent sucrose solution, were not reduced by the addition of calcium glycerophosphate (1 per cent w/v) in the rinse. No changes were observed in plaque accumulation or in the plaque pH fall after sucrose attributable to calcium glycerophosphate. Topical applications of sodium fluoride (2 per cent) tended to inhibit the development of similarly-induced changes but the effect was not statistically significant with the small number of subjects.

Preliminary fractionation of fluoride-binding constituents of human oral Streptococcus sanguis

Streptococcus sanguis H7PR3 took up fluoride (F) during growth in a medium containing 10 parts/106 F. The F in the bacteria was present in several forms. Ninety per cent was in the cytoplasm, of which 40 per cent was either free or loosely bound to substances of mol. wt 100,000; the remainder was tightly bound.