A.D. Eisenberg

Caries Risk Assessment in a Longitudinal Discrimination Study

Our objective was to develop and perfect a model for the assessment of risk of dental caries onset in children. Even though dental caries prevalence in children is continuing to decline, there is still a significant minority for whom it is a problem. In this study, we sought to ascertain whether a set of variables selected in a previous cross-sectional study could be used to differentiate between caries-free six-year-olds who would or would not subsequently present with clinically-detectable caries. A total of 472 caries-free six-year-olds—286 from a fluoridated community and 186 from a fluoride-deficient community-was selected. Clinical examinations for DMFS, dental fluorosis, and plaque were conducted. Stimulated whole saliva was collected for analysis of mutans streptococci, lactobacilli, total viable flora, and fluoride, calcium, and phosphate concentrations. A questionnaire was used for collection of demographic data as well as information on prior fluoride exposure, dietary habits, and oral hygiene practices. By means of linear discriminant analyses, it was possible to predict correctly which children would develop caries within six to 12 months (sensitivity) in 82.8% of cases and which children would not develop caries during that period (specificity) in 82.4% of cases.

Caries Risk Assessment by a Cross-sectional Discrimination Model

Although the prevalence of dental caries is continuing to decline, it still affects a majority of the US population and can be a serious problem for those afflicted. The objective of this project was to develop and perfect a model for assessment of risk of dental caries onset in children. In the first study, reported herein, a set of clinical, microbiological, biochemical, and socio-demographic variables was identified that distinguished, with an acceptable level of sensitivity and specificity, between children who had no previous caries experience and children who had high caries levels. A total of 313 children-age 12-15 years, 140 from a fluoridated community and 173 from a fluoride-deficient community-was selected on the basis of previous caries experience, either zero DMFS or high DMFS (> 6 in the fluoridated or ≥ 8 in the fluoride-deficient community). Clinical exams for DMFS, dental fluorosis, and plaque were conducted. Stimulated whole saliva was collected for analysis of mutans streptococci, lactobacilli, total viable flora, and fluoride concentration. A questionnaire was used for collection of demographic data as well as information on prior fluoride exposure, dietary habits, and oral hygiene practices. By means of discriminant analyses, with use of seven key clinical and laboratory variables, it was possible for zero-DMFS subjects to e classified correctly (specificity) in 77.6% of cases in the fluoridated community and in 86.1% of cases in the fluoride-deficient community. High-caries subjects were classified as such (sensitivity) in 79.3% and 88.1% of cases, respectively.

Use of an Intra-oral Model to Evaluate 0.05% Sodium Fluoride Mouthrinse in Radiation-induced Hyposalivation

The present study was undertaken to evaluate the effect of a twice-daily topical application of a 0.05% NaF mouthrinse on de- and remineralization in the oral cavities of subjects suffering from radiation-induced hyposalivation. Six subjects each wore a bonded intra-oral appliance containing a sound and a demineralized human enamel slab for four weeks. During that period, the subjects used 0.05% NaF rinses, twice daily, instead of the 1.1% NaF gel that had previously been a part of their preventive regimen. Salivary flow rates, plaque pH profiles following a 10% sucrose rinse, S. mutans and lactobacillus counts, fluoride clearance, and enamel microhardness were determined during the study. Sound enamel samples displayed no evidence of demineralization, and the previously demineralized enamel showed remineralization in the outer 50 μm in three of the six subjects. The results suggest that a twice-daily oral rinse with 0.05% NaF can prevent demineralization and enhance remineralization in subjects with radiation-induced hyposalivation.

Correlations between Numbers of Microf lora in Plaque and Saliva

An epidemiologic investigation to reliably identify caries-susceptible subjects by microbiological and chemical assessment of plaque and saliva is currently in progress. As part of that study, the numerical relationships of mutans streptococci, lactobacilli and total viable microflora in plaque and saliva among 12- to 15-year-old children in a fluoridated community were determined. Paraffin-stimulated whole saliva and pooled dental plaque were collected. Each sample was suspended in reduced transport fluid, chilled on ice, and assayed. The bivariate normal distribution was found to be a suitable model for the distribution of the pairs [numbers of bacteria in plaque (log10), numbers of bacteria in saliva (log10)]. Statistically significant positive correlations were found between numbers of mutans streptococci in plaque and saliva, and between lactobacilli in plaque and saliva.

Uptake of Fluoride by Cells of Streptococcus mutans in Dense Suspensions

Fluoride uptake by nongrowing cells of Streptococcus mutans GS-5 was assessed by means of the space technique. Uptake was highly concentrative at low fluoride concentrations or low pH. In all, it appeared that fluoride uptake is predictably related to its weak-acid properties and that fluoride can be used, as certain other weak acids are, to estimate intracellular pH.

Interactions of Sanguinarine and Zinc on Oral Streptococci and Actinomyces Species

Sanguinaria extract, which contains benzophenanthridine alkaloids, has been used as a folk medicine for many years. Minimum inhibitory and minimum bactericidal concentrations (MIC and MBC values) for sanguinarine were determined for common and etiologically important plaque bacteria. Because the efficacy of sanguinarine is believed to be enhanced by zinc, isobolograms were assessed to determine their mode(s) of interaction. Hydrogen ion concentration influenced the inhibitory activity of both sanguinarine and zinc. For sanguinarine, at the optimum pH (6.5), MIC values were 4 or 8 micrograms/ml for Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguis, Actinomyces viscosus and Actinomyces naeslundii. MIC values were 0.125-0.50 mmol Zn/ml. MBC values ranged from 1 to 8 mmol Zn/ml at pH 5.5. Isobologram data revealed that sanguinarine and zinc interacted synergistically. Viadent oral rinse, which contained 300 micrograms sanguinaria extract/ml and 0.2% zinc chloride (14.9 mmol Zn/l), was inhibitory to all strains tested. MIC values were 1 or 2% (ml Viadent oral rinse/100 ml aqueous solution) for all strains except A. viscosus for which the MIC value was 12% (vol/vol).

Interactions of Zinc with Fluoride on Growth, Glycolysis and Survival of Streptococcus mutans GS-5

Effects of zinc and/or fluoride on growth, glycolysis and survival of Streptococcus mutans GS-5 were examined in vitro. Zinc inhibited growth and glycolysis, and enhanced the antimetabolic activity of fluoride. Zinc alone had little effect on cell survival. During cell growth without pH control a protection from cell death was mediated by fluoride, which appeared to be caused by a higher final pH in the culture medium. When cell death was observed under controlled pH conditions in a lactate-acetate buffer at pH 6.5, 5.0 or 4.0, fluoride was bactericidal only at pH 4.0. However, the combination of zinc plus fluoride was strongly bactericidal at all pH values that were tested.

In vitro Demineralization of Enamel by F-sensitive and F-resistant Mutans Streptococci in the Presence of 0, 0.05, or 0.5 mmol/L NaF

Lactate production and accompanying enamel demineralization by fluoride-sensitive and fluoride-resistant mutans streptococci were studied in an in vitro demineralization model in the presence of 0, 0.05, or 0.5 mmol/L NaF. The fluoride-resistant strains were derived from laboratory strains or were recently isolated strains from xerostomic patients on high-dose fluoride therapy. The demineralization model was composed of a cell suspension in a glucose-agarose gel overlying a bovine enamel block. Lactate and calcium content of the agarose were determined after 22-hour incubations at 37°C. Fluoride-resistant variants of Streptococcus sobrinus 6715-15 produced less lactate and caused less demineralization than did the parent strain even in the presence of fluoride. On the other hand, fluoride-resistant variants of Streptococcus mutans C180-2 and of S. mutans GS-5 produced more acid and caused greater demineralization than did their respective parent strains, both in the absence and presence of fluoride. Two recently isolated fluoride-resistant S. mutans strains produced more lactate and demineralized enamel more than did two recently isolated S. mutans strains from normal human subjects, both in the presence of 0 and 0.05 mmol/L NaF. It is concluded that adaptation to fluoride resistance does not invariably reduce the cariogenicity of mutans streptococci nor the effectiveness of fluoride in preventing demineralization.

Effects of Fluoride, Lithium, and Strontium on Growth and Acid Production of Mutans Streptococci and Actinomyces viscosus

Eight strains of mutants streptococci and two strains of Actinomyces viscosus were studied to determine (1) their relative sensitivities to fluoride, lithium, and strontium and (2) whether lithium or strontium interact to enhance the known antimicrobial effects of fluoride. Analyses of variance of the data revealed a major inhibition of growth and acid production by fluoride, but not by lithium or strontium. Fluoride (5 mg/l) inhibited cell growth of all strains tested by a mean of 17% and total titratable acid production by a mean of 31%. However, there were marked differences between the strains. Mean total titratable acid was inhibited by fluoride least with the A. viscosus strains (15%) and most with the mutans streptococci (34%). Although interactions among the elements were statistically significant, they were generally slight in magnitude.

Effects of Fluoride, Lithium, and Strontium on Intracellular Polysaccharide Accumulation in S. mutans and A. viscosus

Fluoride (5 mg/l) consistently depressed the accumulation of intracellular iodophilic polysaccharides (IPS) in Streptococcus mutans strains BHT, FA-1, and GS-5 by over 90% and in Actinomyces viscosus strain RC-45 by over 50%. There was little further reduction in IPS content when fluoride was increased from 5 to 100 mg/l. Lithium (0 to 1 mg/l) neither enhanced nor inhibited IPS accumulation, nor did it modify the inhibitory effects of fluoride in three of the four strains tested. Strontium (0 to 100 mg/l) did not alter IPS accumulation in S. mutans GS-5 but decreased accumulation (<10%) in S. mutans FA-1 and BHT and significantly enhanced IPS accumulation in A. viscosus RC-45. Analysis of variance indicated no statistically significant interactions between fluoride and strontium, fluoride and lithium, or strontium and lithium.