Biomedical subjects
A Tatevossian
Publications and source records attributed to A Tatevossian.
Facts and artefacts in research on human dental plaque fluid.
In 1966, Jenkins suggested that the plaque fluid environment was likely to have higher concentrations of extracellular solutes than was apparent from analyses of total plaque concentrations. Early work on plaque fluid confirmed this contention, but some artefact was also generated by the prolonged centrifugation used for separation. The solute concentrations in plaque fluid mostly exceed those in saliva or crevicular fluid. Thus, the environmental conditions are distinctly different from those based on the assumption that saliva readily permeates films of dental plaque. In contrast, the presence of serum proteins suggests a crevicular input to plaque fluid. These data suggest that exchange between dental plaque and its environment is apparently restricted. Diffusion rates measured in dental plaque by different methods do not agree on how restricted it is. However, measuring diffusion in plaque introduces artefacts in packing density, a major determinant of the diffusion rate. The conditions used for collection and analysis have been reported to produce artefactual changes in plaque fluid potassium, a predominantly intracellular ion. Measurements of predominantly extracellular ions, such as calcium, are no less prone to artefact, whether based on ion-selective electrodes or on total calcium. We have much to learn about the fluid environment of the teeth and about dynamic changes in plaque fluid composition and properties during perturbations. Such information can give insights into pathological processes such as tooth demineralization and dental caries, calculus formation, and gingival inflammation.
Micro-analysis of plaque fluid from single-site fasted plaque.
Despite the site-specific nature of caries, nearly all data on the concentration of ions relevant to the level of saturation of plaque fluid with respect to calcium phosphate minerals or enamel are from studies that used pooled samples. A procedure is described for the collection and analysis of inorganic ions relevant to these saturation levels in plaque fluid samples collected from a single surface on a single tooth. Various methods for examining data obtained by this procedure are described, and a mathematical procedure employing potential plots is recommended.
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)
The buffer capacity of single-site, resting, human dental-plaque fluid.
A carbonate equilibration method was used to measure the buffer capacity of resting plaque fluid collected from single buccal or interproximal sites of upper and lower first molars or anterior teeth. The maximum buffer capacity was 26 m-equiv./l at pH 7.1. The buffer contribution from the measured concentrations of phosphate and carbonate was calculated for each sample. These values were compared with the buffering actually measured and with that expected from organic acids, proteins, and amino acids at average values, as taken from reports in the literature. Relative contributions of buffer species at the average pH of the samples (6.86) were: 35 per cent phosphate, 10 per cent carbonate, 10 per cent protein, 10 per cent organic acids, 2 per cent amino acids, 30 per cent unidentified. There were no significant differences in the buffer capacities of samples originating from sites that differ in their accessibility to saliva. Buffering in resting plaque fluid is more than twice that in saliva and did not show differences correlated with the intra-oral location of the samples.
Extracellular potassium concentrations in human dental plaque fluid recovered from single sites.
Previous studies using potassium ion-selective microelectrodes have demonstrated that potassium concentrations in dental plaque fluid obtained by centrifugation are identical to whole plaque values determined immediately after collection. Such procedures were now used to examine the variations in potassium concentrations between single-site samples of overnight-fasted resting plaque fluid. The potassium concentrations (67.3 +/- 10.8 mmol/l, N = 50) were similar to those found before in whole plaque within 1 min of removal from the mouth and did not appear to be site-dependent. Possible mechanisms for the maintenance of potassium in plaque fluid at higher than salivary levels are described.
Calcium and phosphate in human dental plaque and their concentrations after overnight fasting and after ingestion of a boiled sweet.
The concentrations of ionized and total Ca inorganic and total phosphate were determined in the same pooled samples of fluid separated from 24 h plaque collected from volunteers at least 1 h after a mid-morning snack. About half the total concentration of Ca was ionized (1.53 mM, SD 0.73, n = 36). The mean total Ca concentration (2.88 mM, SD = 0.89, n = 34) was about half that reported previously. The inorganic phosphate was in the range reported previously and comprised about 80 per cent of the total pool of soluble phosphate. A small but significant pool of organic phosphate comprised about 20 per cent of the total phosphate. There were no differences in any of these measurements between plaque-fluid samples pooled from upper buccal posterior teeth and from other sites. The product ([Ca ion] X [inorganic phosphate]) in plaque fluid greatly exceeded saturation levels with respect to potential solid phases present at the enamel surface. Five adults provided overnight-fasted dental plaque for one year to examine the effects of ingesting a boiled sweet on the plaque Ca and phosphate when collected 15 min later. There were no significant differences between fasting control and post-sweet levels of plaque-fluid Ca (ionized and total) and phosphate (inorganic and total). In the post-sweet residue, there were lower total phosphate but not Ca concentrations; the variability in these measurements may explain the unexpected depletion of the organic pool of phosphate in the residue.
Re: The rapid determination of extracellular potassium concentrations in whole human dental plaque and plaque fluid.
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The effects of heat inactivation, tortuosity, extracellular polyglucan and ion-exchange sites on the diffusion of [14C]-sucrose in human dental plaque residue in vitro.
Human dental plaque, accumulated for up to 24 h in vivo was packed into polyethylene tubing (0.5 mm, i.d.) by centrifugation at 5000 g for 15 min at 4 degrees C. [U-14C]-sucrose and carrier sucrose were diffused horizontally from one end and after 6 h, the [14C]-sucrose profile along the tube was quantified by liquid-scintillation counting and a diffusion coefficient was calculated. Compared with water, dental plaque significantly retarded the diffusion of sucrose. In live plaque, retardation of sucrose was less than in killed plaque, due to metabolism of sucrose to faster-diffusing species. Increasing the plaque tortuosity by increasing the centrifugal force used for packing reduced the diffusion rate further. Experimental conditions which increased the concentrations of water-insoluble, ethanol-precipitable extracellular glucan, EPG, in the plaque effected a reduction in the diffusion rate of sucrose. In contrast, an increase in EPG in batch cultures of Streptococcus mutans, serotype c, was associated with an increased rate of diffusion. The presence of ion-exchange sites did not affect the diffusion of sucrose in Sephadex gel models although the tortuosity of their pore structure resulted in a 6.5-fold reduction in the diffusion rate compared with water. Thus the retardation of the diffusion of sucrose in dental plaque is largely explained by the tortuosity of the available diffusion channels and the retardation of diffusion effected by EPG is probably of greater significance in older, thicker and more tightly-packed dental plaque.
Some factors affecting the diffusion of [14C]-lactate in human dental plaque.
The apparent diffusion rate, D, of lactate was significantly retarded in dental plaque fluid and a simulated plaque fluid consisting of a chemically-defined solution of salts, amino acids and albumin in phosphate buffer at pH 6.5. Metabolic utilization of lactate in live plaque residue reduced D for lactate into such samples of residue, compared with killed samples. D in plaque residue was lower than in a previous study. Increasing the packing density of killed plaque residue of Streptococcus sanguis cells reduced D. Pre-incubation of plaque residue with sucrose or sucrose + NaF reduced D for lactate. No such relationship was found when Streptococcus mutans was so treated, but D for lactate was lower when the cells were grown in tryptone-soy broth supplemented with 5 per cent sucrose compared with unsupplemented broth. The retardation of lactate increased with an increase in ion-exchange capacity of cation- and anion-exchange Sephadex gel-model systems. Thus, the apparent diffusion coefficient of lactate in dental-plaque residue is influenced by the chemical composition of the plaque aqueous phase, by metabolism of lactate, by plaque tortuosity, sucrose metabolism and ion-exchange interactions.
Diffusion of small ionic species in human saliva, plaque fluid and plaque residue in vitro.
The tracer diffusion of small ionic species was investigated in water, saliva, dental plaque fluid and in plaque residue packed by a range of g forces. Diffusion rate of NaCl was similar in water, saliva and plaque fluid. The rate of CaCl2, NaH2PO4, Na2HPO4 and Na2SO4 was less in both saliva and plaque fluid. Diffusion rate of all ionic species tested was significantly less in plaque residue, most of all for CaCl2. In plaque fluid, plaque residue and water, an inverse linear relationship was found between log diffusion coefficients and log molecular weights. Increasing the tortuosity of the diffusion path, by packing plaque residue, further reduced the diffusion rate of NaH2PO4 and NaHCO3. In terms of three-dimensional diffusion, in plaque fluid, NaH2PO4, Na2HPO4 and CaCl2 diffused a distance of 300 microns within 25 s, whereas in plaque residue the equivalent diffusion times were 1.5-5.7 min. The unique retardation of CaCl2 in plaque residue implicated both non-specific and specific binding interactions.
Hydrolysis of some carbohydrate substrates by enzymes of pooled human dental plaque fluid.
The activity of enzymes releasing glucose and reducing sugars from sucrose, maltose, starch and dextran was compared in the same pooled samples of plaque fluid (PF) from 24 h human dental plaque. Equimolar amounts of glucose and fructose were released from sucrose in 3 h incubations. Reducing activity was released from sucrose or starch at a similar rate. The rate of glucose release from the starch substrate was similar to that from maltose but lower than that from sucrose. Raffinose was hydrolysed, indicating beta-fructosidase activity in PF. The hydrolysis of maltose, trehalose and melezitose confirmed the presence of alpha-glucosidase activity. Maltose was metabolized partially to a maltosaccharide. No dextranase activity was detectable in PF, and the soluble polymeric carbohydrate in PF was partially degraded by fungal dextranase. Starch was degraded to dextrins, maltose and glucose.
Electrophoretic and immunoelectrophoretic studies of proteins in the aqueous phase of human dental plaque.
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Fluoride and magnesium in dental plaque.
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The kinetics of inorganic phosphate in human dental plaque and saliva.
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Enzymic activities in the aqueous phase of human dental plaque.
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Neuraminidase activity in human dental plaque fluid.
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Diffusion of radiotracers in human dental plaque.
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