A study of inorganic constituents in dental plaque

Composition and cariogenic potential of dental plaque fluid

Our understanding of the chemical events that take place at the tooth-plaque interface has improved greatly through studies of the chemical composition and properties of dental plaque fluid. In the absence of fermentable carbohydrate, plaque fluid has been found to be supersaturated with respect to tooth mineral and other calcium phosphate phases, thus exhibiting the potential to support calculus formation and the remineralization of incipient carious lesions. Following the exposure to fermentable carbohydrate, the degree of saturation of plaque fluid decreases rapidly, primarily due to lactic acid production and the lowering of plaque fluid pH. The extent of these chemical changes has been shown to be associated with differences in caries history. Such studies have been facilitated by the recent development of microanalytical techniques. Unfortunately, little is known about the relationship between the observed chemical changes in plaque fluid and the microbial composition of plaque. Limited information is also available on the association of immune factors in plaque fluid with dental disease.

The antimicrobial action of fluoride and its role in caries inhibition

Despite a considerable amount of literature on the effects of fluoride in dental plaque, several urgent questions remain unanswered, such as: Does the inhibiting effect of fluoride on dental plaque metabolism contribute to caries prevention? Does adaptation of plaque to fluoride affect its cariogenicity? Single applications of fluoride directly to dental plaque reduced acid production. Also, fluoride dissolving from topically treated enamel reduced the acid production in covering layers of oral bacteria in vitro. The effects of both treatments were only of short duration and may not be relevant to caries prevention in vivo. In contrast, daily applications of fluoride resulted in a reduction of the acidogenicity of dental plaque even 8-12 h after the treatment. Such a reduction is likely to contribute to caries prevention. But it has to be realized that when plaque reaches saturation with respect to fluoridated calcium (phosphate) precipitates, enamel becomes insoluble and any antimicrobial effect becomes irrelevant. Still lacking are data on the antimicrobial effects of fluoride regimens normally used in home care, in weekly rinsing programs in schools, or treatments applied professionally every six months. Adaptation of Streptococcus mutans to fluoride has been suggested to reduce the cariogenic potential of the cells. In vitro-induced fluoride-resistant strains were less cariogenic in rats, and the velocity of acid production in vitro was reduced at constant pH greater than 5.5. Despite the ability of oral bacteria to adapt to fluoride, evidence of adaptation in dental plaque of normal subjects resulting in a reduced cariogenic potential has not yet been demonstrated.

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)

Fluoride concentration in dental plaque of naval recruits with and without caries

Plaque samples were evaluated for fluoride concentration, the degree of the fluoride binding and uptake of fluoride from 1 and 225 parts/10(6) F solutions. The plaque of the caries-free individuals contained significantly higher fluoride concentrations, but no difference was found in binding strength between the caries-free and caries-active groups. Uptake of fluoride from a 1 part/10(6) solution was slightly less for plaque of caries-free recruits, but there was no difference between the groups in uptake from the more concentrated solution.

Fluoride accumulation by oral microorganisms

Ten laboratory strains of oral microorganisms and 17 recent clinical isolates were examined for their ability to concentrate fluoride from a 1 ppm (0.05 mM NaF( fluoride solution. The laboratory strains concentrated the ion from two- to six-fold over the surrounding media. Clinical isolates of Actinomyces concentrated the ion to similar levels to the laboratory strains of this organism; however, clinical isolates of Streptococcus mutans and S. sanguis concentrated the fluoride significantly less than any of the laboratory strains examined.

Microflora and chemical composition of dental plaque from subjects with hereditary fructose intolerance

We compared the microbiological and chemical composition of dental plaque from subjects with hereditary fructose intolerance who restrict their dietary sugar intake with that of control subjects who do not. The two groups showed no significant differences in chemical composition of plaque: the mean protein, carbohydrate, calcium, magnesium, and phosphate contents were similar. Dental plaque from both groups contained similar numbers of total colony-forming units per microgram of plaque protein, and Streptococcus sanguis, an indigenous nonpathogen, was isolated with equal frequency from plaque samples of both groups. However, potentially odontopathic Streptococcus mutans and Lactobacillus were isolated three to four times more frequently from plaque samples of control subjects than from plaque samples of subjects with hereditary fructose intolerance. Clearly, diet (sucrose in particular) influences the colonization and multiplication of specific cariogenic organisms in dental plaque.

Effect of sodium fluoride on the viability and growth of Streptococcus mutans

A fluoride-sensitive (FS) strain of Streptococcus mutans and a laboratory-induced fluoride-resistant (FR) offspring were compared for the effects of sodium fluoride on viability and growth. There was a significant fluoride-related loss of viability in resting cell suspensions of the FS strain during a 47-hour exposure to fluoride levels above 75 ppm that was not encountered with the FR strain. The addition of 300 ppmF to actively growing six-hour broth cultures almost totally arrested the growth of the FS strain, while only slightly reducing that of the FR culture. The addition of 600 ppmF immediately terminated FS growth, and greatly reduced the rate and maximum growth of FR cultures.

Fluoride content of dental plaque before, during and after ingestion of sucrose modified with fluoride or bicarbonate-phosphate

Students ingested tablets daily during a period of 3 d growth of dental plaque and in connection with the collection of plaque specimens. The tablets varied in composition: sucrose (C), sucrose containing sodium bicarbonate-monopotassium orthophosphate and fluoride (BPF), and sucrose modified with fluoride (F). The daily fluoride dose in conjunction with the growth of plaque and the collection of specimens was 0.5 mg of total fluoride and 0.2 mg in the determination of ionized fluoride. The fluoride taken during the growth period did not significantly affect the total and ionized fluoride contents of the plaque. During the consumption of all the tablets, the total fluoride content of the plaque increased temporarily, after which a drop took place to close to the original value. In the case of the C- and the BPF-tablets, the increase was statistically significant (P-values less than 0.02 and less than 0.001, respectively). During the consumption of the BPF- and F-tablets, the ionized fluoride content dropped significantly (P-values less than 0.001 and less than 0.01, respectively). The investigation showed that a binding of the free fluoride ions in dental plaque takes place in connection with fermentation.

Concentration of fluoride in plaque - a possible mechanism

A mechanism of concentration of fluoride (and phosphate) ions in plaque is suggested: calcium ions from saliva are bound to fixed acidic groups in the plaque, and fluoride (or phosphate) ions are attracted to the bound calcium as counterions. The principle was demonstrated by equilibrium dialysis of calcium-treated acidic ionic exchange material (Sephadex SP and CM) against 1 part/10(6) of fluoride. A part of the fluoride was found to be bound under these conditions.

Associations between the total fluoride content of dental plaque and individual caries experience in Australian children

Individual caries experience (DMFT) and the total fluoride content of dental plaque were determined for 72 schoolchildren, aged 9.7-13.0 years, lifelong residents in one of three New South Wales towns, where the fluoride levels of the reticulated water supplies were: Katoomba, less than 0.1 parts/10(6); Sydney, 1.0 parts/10(6) for 4 years; and Yass, 1.0 parts/10(6) for 16 years, prior to sampling. The mean fluoride content of plaque in Sydney (22.6, s.d. = +/- 16.8 parts/10(6)) and Yass (25.6, s.d. = +/- 16.4 parts/10(6)) differed significantly (t = 2.27, P less than 0.05 and t = 3.30, P less than 0.02, respectively) from that in Katoomba (13.5, s.d. = +/- 8.3 parts/10(6)). Significant inverse associations were demonstrated between total plaque fluoride and individual caries experience (DMFT) in Sydney (r = -0.45, P less than 0.025) and overall (r = -0.28, P less than 0.010). Inverse trends were established between plaque quantity (dry weight of plaque collected) and fluoride levels. No associations could be demonstrated between fluoride treatment (dentifrice, tablets or topical application) and plaque fluoride, DMFT or plaque quantity.

Degrees of saturation with respect to apatites in parotid saliva at various ph values

The purpose of the present work was to investigate the degrees of saturation with respect to hydroxyapatite and fluorapatite in saliva at various pH's. The data of ionic activities in parotid saliva were collected from the literature and the degrees of saturation with respect to hydroxyapatite and fluorapatite were calculated. It was found that parotid saliva was supersaturated with respect to both apatites above pH 5.5, unsaturated with respect to hydroxyapatite and concurrently supersaturated with respect to fluorapatite in the pH range 5.5-4.5, while it was unsaturated with respect to both apatities below pH 4.5. In the laboratory it has been found that when enamel is exposed to a liquid unsaturated with respect to hydroxyapatite and supersaturated with respect to fluorapatite, a caries-like lesion is developed. A liquid unsaturated with respect to both apatites leads to an erosion-like injury. It is concluded that the two chemical conditions leading to the two types of enamel lesions may both occur in the oral cavity.

Plaque acid production in hamsters pretreated with fluoride

Plaque acid production in hamsters pretreated with fluoride did not differ from that in untreated control hamsters, although sufficient fluoride was present in the teeth of the treated hamsters to protect against a severe cariogenic challenge. The results indicate that enamel-bound fluoride does not significantly influence carbohydrate metabolism of microbial plaques.