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Biomedical subjects

H C Margolis

Publications and source records attributed to H C Margolis.

At least 37 records · Page 2Linked to original sources
PubMed1993

Effect of fluoride incorporation into human dental enamel on its demineralization in vitro.

Coronal surfaces of extracted human teeth were ground to a depth of about 1 mm and then cut in half labiolingually. One half was used as a control; the other half was exposed, for 3 days, to a fluoride-enriching buffer (0.1 mol/l lactic acid, 19.7 mmol/l CaCl2, 10.8 mmol/l KH2PO4, 3 mmol/l NaN3; pH adjusted to 4.68 with KOH) having fluoride concentrations from 0.0002 to 2.2 parts/10(6). This exposure resulted in an uptake of fluoride by the enamel to a depth of 2 microns without any apparent demineralization. The fluoride uptake was proportional to the F concentration of the enriching solution, reaching concentrations of about 8000 parts/10(6) within the first micrometre of enamel exposed to the highest F concentration; the controls had uniform F concentrations not exceeding 50 parts/10(6) along the 2.5 microns of enamel depth sampled. Thin sections (140-160 microns) were cut perpendicularly to the lingual surface, coated with protective resin except for a window about 1 mm long on the ground lingual surface, and exposed to a demineralizing buffer. The mineral losses of the sections were followed over 5 days by microradiography and image analysis. Fluoride enrichment resulted in reduced demineralization and the reduction was inversely related to the enamel fluoride content. The controls displayed a uniform erosion of the surface enamel whereas all the treatments below 1.5 parts/10(6) in the enriching solutions developed typical subsurface 'lesions'. The mineral content of the surface layer increased with increasing time of exposure to the demineralizing buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Buffers↗
PubMed1993

Cariogenic potential of pooled plaque fluid from exposed root surfaces in humans.

The composition of pooled plaque fluid from exposed root surfaces of five population samples was determined before and at selected times (3, 7 and 15 min) after a 5 and 10% sucrose rinse. Subjects were 45-65 yr old, had exposed, sound root surfaces, and were grouped according to root caries status [caries-free (CF), no root caries history; caries-positive (CP), recorded root caries experience]. Samples were obtained only from the sound surfaces of the CF and CP subjects after overnight fasting. Plaque samples from each subgroup were pooled under mineral oil and maintained on ice. Plaque fluid was then isolated by centrifugation and analysed for organic acids and inorganic ions (ion chromatography), and pH (microelectrodes). From these data, the degree of saturation [DS(TM)] in plaque fluid with respect to tooth mineral (TM) was calculated. Before exposure to sucrose, plaque fluids from the CF and the CP subgroups had similar ionic compositions. These fluids were also found to be supersaturated with respect to tooth mineral. After exposure to sucrose, a rapid decrease in plaque fluid pH was observed, which corresponded primarily to lactic acid production. For all times examined, mean pH and DS(TM) values were lower and lactic acid concentrations were higher in the CP than the CF samples. Lower values of DS(TM) suggest that plaque fluid from CP subjects had a measurably greater cariogenic potential. Calcium concentrations also increased significantly and to comparable levels in all plaque fluid samples after sucrose exposure, despite lower acid production in CF samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed1993

Effect of sucrose concentration on the cariogenic potential of pooled plaque fluid from caries-free and caries-positive individuals.

Pooled plaque samples were obtained from (1) coronal surfaces of two groups of caries-free (CF) subjects, (2) coronal 'white-spot' surface areas of a group of caries-positive (CP) subjects, and (3) exposed, sound root surfaces of root caries-free (RCF) and root caries-positive (RCP) subjects. The plaque samples were obtained before and 3 min after a 1 min rinse with a 0.5, 1, 2, 5 and 10% sucrose solution. Plaque fluid was then isolated from each plaque sample by centrifugation and analyzed for inorganic ions, organic acids, and pH values. With increasing sucrose concentration: (1) plaque fluid pH and the degree of saturation (DS) with respect to tooth mineral decreased; (2) the pH and DS values of CP and RCP samples were consistently lower than those of CF and RCF samples, respectively; (3) plaque fluid lactic acid concentrations increased and were consistently higher in the CP and RCP samples than in the CF and RCF samples, respectively, and (4) plaque fluid lactic acid concentrations leveled off between 1 and 5% sucrose; this occurred at lower sucrose concentrations with CP and RCP samples than with CF and RCF samples, respectively. RCP samples contained consistently higher levels of mutants streptococci than RCF samples. The chemical composition of plaque fluids, following sucrose exposure, were found to correlate well with caries history. The observed differences in lactic acid concentrations in samples from CF and CP subjects are discussed with regard to differences in microbiological composition and possible differences in plaque permeability to sucrose.

Adolescent↗
PubMed1993

The association of mutans streptococci and non-mutans streptococci capable of acidogenesis at a low pH with dental caries on enamel and root surfaces.

Coronal dental plaque from each of 12 caries-positive subjects (Group I) was pooled from "white spot" tooth surface areas and, separately, from sound surface areas; sound surface areas in each of 18 caries-free subjects (Group II) were sampled similarly. Two samples, one consisting of material from a root-surface lesion and another of plaque from a sound root-surface area, were obtained from each of another 10 subjects (Group III). The samples from Groups I and II were evaluated for: (1) pH-lowering potential in vitro with dispersed plaque suspensions, excess glucose supply, and a 60-minute test; (2) the levels of mutans streptococci (MS) and lactobacilli; and (3) the distribution of the predominant non-mutans streptococci (non-MS) according to their final pH in glucose broth; only microbial analysis was done for the Group III samples. The levels of the MS were generally positively associated with caries. A weaker positive association was found for the levels of those non-MS capable of acidogenesis at low pH (final pH < 4.4). The latter generally far outnumbered the MS in all types of samples. The levels of lactobacilli were nearly always very low. The pH-lowering potential (final pH and pH drop rate) was higher for plaque from "white spot" areas than for plaque from sound surface areas (Group I). The samples from caries-free subjects (Group II), however, exhibited a pH-lowering potential which was not significantly different from that of both types of samples from the caries-active subjects (Group I).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Kinetics of hydroxyapatite dissolution in acetic, lactic, and phosphoric acid solutions.

The present study was undertaken in an attempt to relate the kinetics of hydroxyapatite dissolution to solution parameters, under experimental conditions relevant to the dental caries process. Thus, the dissolution of hydroxyapatite was studied in acetic, lactic, and dilute phosphoric acid solutions having initial pH values from 4 to 6. Rates of dissolution and the corresponding degree of saturation with respect to hydroxyapatite were determined at various times throughout the dissolution process. Rates of dissolution of all solutions were found to decrease with increasing degree of solution saturation and were greater in solutions with lower initial values of pH. However, rates of dissolution in partially saturated phosphoric acid solutions (without added organic acid) were at least one order of magnitude lower than those observed in the organic acid buffers with the same initial pH, over the same range of saturation values. The data obtained are consistent with a surface-controlled dissolution model in which the rate of dissolution is dependent upon the degree of saturation and the sum of the activities of the acidic species in solution, i.e., phosphoric and organic acids. These results suggest that in order to assess the cariogenic potential of a given medium (e.g., plaque fluid), one must determine both the degree of saturation with respect to the dissolving mineral and the activities of acidic species in solution.

Acetates↗
PubMed1992

Composition of pooled plaque fluid from caries-free and caries-positive individuals following sucrose exposure.

The composition of pooled plaque fluid from five population samples was determined before and at selected times (7, 15, 30, and 60 min) after a 10% sucrose rinse. Subjects were grouped according to caries status (caries-free, CF, DMFS = 0; caries-positive, CP, DMFS > 10). Samples were also studied from white-spot surfaces and from sound surfaces of the same mouths of two additional CP groups. Plaque fluid was isolated by centrifugation and analyzed for organic acids, inorganic ions (ion chromatography), and pH (microelectrodes). Prior to sucrose exposure, plaque fluids from the CF subgroups and from sound surfaces of the CP subjects had higher pH values than samples from CP subgroups and from white-spot surfaces, respectively; the ionic compositions were otherwise similar. Starved plaque fluids were also found to be supersaturated with respect to enamel and to a significantly greater degree in the CF samples, suggesting that CF plaque fluid may have a greater remineralization potential than CP samples. Following sucrose exposure, a rapid decrease in plaque fluid pH was observed, which corresponded primarily to lactic acid production. For all times examined, mean pH and DS(En) values were lower and lactic acid concentrations were higher in the CP samples than in the CF samples; noted differences were statistically significant at 7 min for pH and DS(En), and at 7, 15, and 30 min for lactic acid. Lower values of DS(En) suggest that plaque fluid from CP subjects had a measurably greater cariogenic potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

An assessment of recent advances in the study of the chemistry and biochemistry of dental plaque fluid.

This paper discusses key points made during the symposium in the light of work carried out in other laboratories. It is emphasized that the unique importance of plaque fluid is that the net result of chemical changes induced by microbial activity is reflected in this medium, which is in intimate contact with the enamel surface, and that this medium is accessible to chemical and biochemical analyses. However, in order to assess the cariogenic potential of plaque, we must consider the properties of both whole plaque and plaque fluid together. Although it is apparent that results of plaque fluid composition are sensitive to both isolation and the storage procedures utilized, plaque fluid appears to be a distinct entity within the oral cavity. Technical advances have been made which allow for the determination of the activity of selected ions (hydrogen, calcium, phosphate, potassium, fluoride) in plaque fluid obtained from a single site within the mouth. It appears, however, that such data alone may be insufficient to define the cariogenic potential of plaque appropriately. Evidence is presented from which it can be concluded that, with use of pooled samples of plaque obtained from individuals with clear differences in caries experience, results on plaque and plaque fluid composition can be obtained which are consistent with noted differences in caries susceptibility. The importance of base production is also discussed, and it is noted that few studies have been carried out to elucidate the role of proteins found in plaque fluid. In conclusion, recent advances in the study of plaque fluid have provided new insights into the mechanism of caries formation which are also germane to the formation of dental calculi.

Data Collection↗
PubMed1990

Physicochemical perspectives on the cariostatic mechanisms of systemic and topical fluorides.

The cariostatic mechanisms of systemic and topical fluoride agents are considered in light of a previously proposed model for the caries process. It is noted that fluoride, in principle, can induce a cariostatic effect: by (1) reducing enamel solubility when incorporated into the mineral structure; (2) by fostering the remineralization of incipient enamel lesions and the deposition of fluoridated phases (within dental plaque) which provide a source of mineral ions (Ca, P, F) under acidic conditions; and (3) by reducing the net rate of transport of matter out of the enamel surface, under acidic conditions, by inducing the reprecipitation of fluoridated hydroxyapatite phases within enamel. It is also noted that relatively high (approximately 12,000 ppm) concentrations of professionally applied topical fluorides significantly reduce the rate of acid production of cariogenic organisms (e.g., S. mutans). Based on an analysis of available clinical and laboratory data, it is concluded that the benefits provided by water fluoridation result, to a large degree, from a topical effect. It is suggested that clinical procedures be developed to establish and maintain low levels of free fluoride in plaque fluid. It appears that this will require frequent exposure to topical fluorides.

Cariostatic Agents↗
PubMed1988

Composition of human plaque fluid.

The composition of pooled resting plaque fluid was determined in four groups of college-age students (18-22 years), each composed of 50 individuals, who abstained from oral hygiene for 36 hours and did not eat or drink for at least one hour prior to plaque collection. Plaque samples from each group were pooled under mineral oil in small centrifuge tubes and centrifuged at 37,000 g for one hour at 4 degrees C. Supernatants were then combined under mineral oil and centrifuged at 5000 g (4 degrees C) for 15 minutes. In general, the inorganic composition of plaque fluid in the four groups was quite similar and in agreement with values reported by other investigators, but quite different from those of saliva or serum. The mean composition was: Ca, 7.07 +/- 0.51 mmol/L; P, 23.2 +/- 5.3 mmol/L; Na, 18.6 +/- 2 mmol/L; K, 85.1 +/- 5.3 mmol/L; Mg, 3.9 mmol/L; Cl, 42.8 +/- 9 mmol/L; F, approximately 0.004 mmol/L; pH, 5.69 (5.63-6.01). Acetate, propionate, succinate, butyrate, lactate, and formate were determined in two samples analyzed, with acetate and propionate being the predominant acids found. It was also demonstrated, through the titration of one of the plaque fluid samples, that the observed buffer capacity in plaque fluid was mostly related to its organic acid composition. It was noted, however, that when the initial pH in plaque fluid exceeded 6.5, phosphate contributed significantly to the buffer capacity. The contribution of other soluble species (proteins, peptides, amino acids) to the observed buffering in plaque fluid appeared to be small.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Composition of pooled resting plaque fluid from caries-free and caries-susceptible individuals.

The composition of pooled resting plaque fluid from 10 population samples, grouped according to age (8-11, 14-17, 18-25 years) and caries status (caries-free, CF, DMFS = 0; caries-susceptible, CS, DMFS greater than 10), was determined by means of ion chromatography. Subjects received a dental prophylaxis one week prior to plaque collection, abstained from oral hygiene for 48 hours, and did not eat or drink for at least one hour prior to plaque collection. Plaque samples from each group were pooled under mineral oil and centrifuged (15,000 g) for 45 minutes at ambient temperature. Supernatants were analyzed for organic acids, inorganic anions, mono- and divalent cations, and pH value. The ions Na+, NH4+, K+, Ca2+, Mg2+, Cl-, and phosphate were present in all samples. Acetic and propionic acids were predominant, comprising over 75% of the acid (anions) present under resting conditions. Succinic, lactic, formic, and butyric acids were present in lower concentrations. Within each age group, the mean values for pH and NH4+ concentration were higher in the caries-free group; the differences between mean values (CF: pH, 6.35; NH4+, 52 mmol/L; CS: pH, 5.85; NH4+, 37 mmol/L) were found to be statistically significant (p less than 0.05) when all data for the CF and CS groups were combined. Significantly higher concentrations of Mg2+ and butyric acid were also found for the combined CF data. Concentrations of all other constituents were similar. Calculations indicate that plaque fluid is supersaturated with respect to enamel mineral and dicalcium phosphate dihydrate, with a significantly higher degree of saturation with respect to enamel mineral in the CF group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Composition and buffer capacity of pooled starved plaque fluid from caries-free and caries-susceptible individuals.

The composition of pooled starved plaque fluid from six population samples, grouped according to age (8-11, 12-16, 8-17, 18-22 years) and caries status (caries-free, CF, DMFS = 0; caries-susceptible, CS, DMFS greater than 10), was determined by means of ion chromatography. Prior to plaque collection, all subjects abstained from oral hygiene for 48 hours and fasted overnight. In addition, selected subjects also received a dental prophylaxis one week prior to plaque collection. Plaque samples from each group were pooled under mineral oil and centrifuged at 15,000 g (ambient temperature) for 45 minutes. Supernatants were then analyzed for organic acids, inorganic anions, and mono- and divalent cations. Plaque fluid samples from CF and from the CS subgroups were also titrated with standard HCl for exploration of the inherent buffer capacity. The ions Na+ NH4+, K+, Ca2+, Mg2+, Cl-, phosphate, and carbonate were present in all samples analyzed. Formic, acetic, propionic, butyric, and trace amounts of isobutyric and isovaleric acids were detected, with acetic and propionic acids comprising between 85 and 94% of the total acids. Little (less than 1 mmol/L) to no succinic or lactic acid was detected in starved plaque fluid. No apparent difference was detected in the composition and saturation status of pooled starved plaque fluid from CF and CS individuals. These results suggest that caries susceptibility is not necessarily correlated with the plaque fluid composition of pooled starved plaque. In addition, no apparent difference in the inherent buffer capacities of these samples could be detected, consistent with the noted similarities in composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Effect of low levels of fluoride in solution on enamel demineralization in vitro.

The effect of low levels of fluoride in solution on in vitro enamel demineralization has been studied. Extracted human teeth were exposed to 0.1 M lactate solutions (at pH 4.3) which were partially saturated with respect to enamel mineral and which contained between 0.004 and 1 ppm fluoride. Enamel demineralization was monitored using SEM and polarized light microscopy. It was observed that, in the absence of fluoride, rapid enamel demineralization occurred, resulting in the formation of cavitations within 72 hours. Using the same demineralizing medium containing as little as 0.024 and 0.054 ppm fluoride, we observed a remarkable protection of the enamel surface. Subsurface enamel demineralization was, however, observed under these conditions as well as in a solution containing 0.154 ppm fluoride. When the demineralizing solution containing 1 ppm fluoride was used, no mineral loss was detected. The observed inhibition of enamel demineralization was also shown to be associated with a significant uptake of fluoride by the enamel mineral. These observations have been noted to correlate with an increase in solution supersaturation with respect to fluoridated apatitic species. The results obtained were found to be consistent with a proposed hypothesis that the net rate of enamel demineralization will be reduced in a demineralizing medium supersaturated with respect to less soluble fluoridated phases, due to the enhancement of the precipitation rate of fluoridated apatitic phases relative to the rate of dissolution of the original enamel surface.

Dental Caries↗
PubMed1985

Importance of high pKA acids in cariogenic potential of plaque.

Through the use of computer simulation, it is shown that anions of high pKA acids (e.g., acetic, propionic, butyric), present in resting plaque fluid, act as effective buffers during the production of stronger acids (e.g., lactic) by oral micro-organisms. Using reported organic acid compositions for plaque, obtained from caries-resistant and caries-susceptible individuals, analyzed at various times following sucrose exposure, it is shown that the calculated pH values of the aqueous phase of plaque describe typical Stephan curves. Furthermore, it is shown that for higher acid anion contents in resting plaque, a higher degree of saturation of the aqueous plaque phase with respect to enamel is maintained during acid production, resulting in a lower demineralization potential of plaque. Enamel demineralization experiments conducted in vitro confirmed the significance of the results of the computer simulations, thus providing evidence for a correlation between the known metabolic activity of plaque (organic acid composition), physical chemistry of plaque, and caries susceptibility.

Acetates↗
PubMed1985

Micro-analytical determination of pH, calcium, and phosphate in plaque fluid.

Micro-analytical techniques for the determination of calcium, phosphate, and pH in a small volume (less than 0.25 microliter) of plaque fluid are described and evaluated. The accuracy and the precision of the techniques were compared with those for standard macrotechniques applied to a large pooled plaque fluid sample. The results obtained for the micro-analysis of pooled plaque fluid were in excellent agreement with those obtained by macromethods. The described techniques were also used to analyze plaque fluid obtained from single quadrants of the oral cavities of five individuals. In this fashion, it was determined that, although a significant variation in plaque fluid composition exists between the quadrants, a greater variation exists between subjects. Analyses of plaque fluid obtained from six individuals, following sucrose exposure, were also conducted. The pH value of the fluid changed with time, following a typical Stephan curve, with a minimum value occurring between 15 and 30 minutes; following this, the pH increased to a value near that for resting plaque. An inverse relationship between pH and calcium and phosphorus concentrations was observed. It is noted that the described techniques are sensitive enough to carry out the above analyses both accurately and precisely using plaque obtained from a single quadrant.

Adult↗
PubMed1982

Effect of fluoride on crystal growth of calcium apatites in the presence of a salivary inhibitor.

The effect of fluoride on the kinetics of crystal growth of calcium apatites was studied using seed crystals of hydroxyapatite coated with PRP-3, a proline-rich phosphoprotein salivary inhibitor of crystal growth. Initial precipitation rates in the presence of PRP-3, under conditions of partial inhibition, were enhanced by fluoride, effectively counteracting the inhibitory activity of the macromolecule. This rate enhancement is related to an increase in the precipitation driving force, i.e., the degree of supersaturation with respect to the precipitating phase; in this case a fluoridated hydroxyapatite. The growth of this phase takes place at the uncovered crystal growth sites which have been previously shown to be the same sites as the adsorption sites for the protein inhibitors. Explanations based on fluoride activation of secondary crystal growth sites and on the displacement of adsorbed inhibitor by fluoride are not substantiated by the present results. It has been demonstrated that under conditions of maximum coverage of available crystal growth sites by PRP-3, resulting in no apparent crystal growth, measurable crystal growth is observed upon the addition of fluoride (1 ppm). This phenomenon is best explained by the fact that at maximum PRP-3 coverage, a small number (16%) of crystal growth sites remain uncovered, which support an unmeasurable rate of crystal growth. Upon the addition of fluoride, this rate is significantly enhanced. It is suggested that the fraction of uncovered growth sites is related to steric interactions of the PRP-3 molecule in the adsorbed state. Overall, the results presented suggest that fluoride can accelerate crystal growth in an environment such as the enamel surface where the acquired pellicle is formed.

Crystallization↗