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Biomedical subjects

E I Pearce

Publications and source records attributed to E I Pearce.

At least 55 records · Page 3Linked to original sources
PubMed1987

The concomitant deposition of strontium and fluoride in dental plaque.

We have investigated the feasibility of incorporating Sr into dental plaque by means of an enzyme-dependent system known to increase Ca, P, and F levels in plaque. A solution containing Ca (20 mmol/L), P (12 mmol/L), MFP (4.7 mmol/L), F (0.3 mmol/L), and urea (500 mmol/L) was modified by equimolar replacement of Ca with 1, 2, 5, and 10 mmol/L Sr. Thin films of human salivary sediment incubated in these solutions showed increasing levels of acid-extractable Sr as the solution Sr increased. When the concentration exceeded 2 mmol/L, deposition of Ca, P, and F was reduced. In artificial plaque, grown on bovine enamel, from mixed human salivary organisms and treated with the solution containing 2 mmol Sr/L, there was a slightly smaller uptake of Ca, P, and Sr, but a greater uptake of F than in sediment treated with the same solution. Natural human plaque treated 12 times in vivo over three days with this solution (in the form of a mouthrinse) also showed substantial increases (from five- to 26-fold) in the concentrations of all four ions. Absolute levels of Ca, P, F, and especially Sr were, however, lower than those in the artificial plaque samples. (Ca + Sr)/P ratios suggested apatite deposition, and the correlation between amounts of Ca and Sr deposited in natural plaque samples suggested that Sr, like F, is structurally incorporated into this apatite. Fluctuations in the pH of natural plaque may promote apatite crystal maturation, causing a slow loss of Sr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Kinetics and product stoichiometry of ureolysis by human salivary bacteria and artificial mouth plaques.

Ureolysis was investigated in salivary bacteria from persons with widely-differing oral ureolytic activities. Rate curves and product stoichiometry were established for urea disappearance, ammonia appearance and conversion of [14C]-urea to 14CO2. Ammonia, released stoichiometrically from urea, was best measured by a direct phenate-hypochlorite reaction. About 80 per cent of the urea-C was liberated as free CO2. Slight deviations from ammonia stoichiometry and most of the CO2 loss occurred in the first 5-10 min of reaction, when the rate of urea disappearance was constant and up to 2-fold higher than subsequently. This rate-change suggests that flux in the ureolysis pathway may be under feedback control. Ureolysis by salivary-sediment bacteria followed Michaelis-Menten kinetics with a Km of 2.5 mM; rates of end-product formation were independent of urea concentration between 25 and 500 mM. Ureolysis was inhibited 98 per cent by 5 mM acetohydroxamic acid, a urease inhibitor, and could be partly solubilized by sonication to give an enzyme preparation which, without cofactor supplementation, quantitatively hydrolysed urea. Thus urea metabolism by oral bacteria may principally involve urease-catalysed hydrolysis, rather than non-urease pathways.

Ammonia↗
PubMed1985

Remineralization of softened bovine enamel following treatment of overlying plaque with a mineral-enriching solution.

Pre-softened, gauze-covered bovine enamel blocks were worn in the buccal sulcus of five subjects for seven days. Artificial plaque enmeshed in the gauze was treated four times per day for four days with an enzyme-dependent mineralizing solution, resulting in 20-, 10-, and 200-fold increases in Ca, P, and F, respectively. Enamel beneath this mineral-enriched plaque recovered 37% of the hardness lost from pre-softening, while control enamel beneath untreated plaque recovered only 14%. Test enamel contained from five to 13 times as much F as did control enamel in the outer four layers sampled. Even though direct use of the mineralizing solution without the interposition of plaque caused a hardness recovery and F uptake similar to those in test enamel in vivo, a direct solution effect on enamel is not thought to explain the in vivo effects. Plaque treated with the urea-containing solution rapidly reaches a pH greater than 8, when a precipitate develops, leaving much-reduced ion concentrations in solution. Direct exposure of softened enamel to such a supernatant resulted in reduced hardness recovery and F uptake. It is concluded that the in vivo enamel remineralization was due mainly to the presence of a mineral phase in the overlying plaque. This mineral could have promoted remineralization by creating mildly supersaturated conditions during normal plaque pH cycles.

Adult↗
PubMed1985

Immediate and delayed effects of an enzyme-dependent mineralizing mouthrinse on dental plaque.

Twenty-two children aged 13 to 14 years rinsed for 3 X 1 min periods with a supersaturated calcium phosphate solution containing urea and monofluorophosphate. Plaque sampled one min after the last rinse showed a marked increase in water-extractable F and a smaller increase in Ca but no increase in water-extractable P. Water-insoluble forms of all three ions were elevated, however. The mean plaque pH was 8.28. Plaque sampled 24 hr after the last rinse showed significant increases in water-insoluble F and Ca only, and no increase in pH. The prompt pH rise and disappearance of water-soluble P suggest that, on exposure to the mineralizing solution, urea and monofluorophosphate are rapidly hydrolyzed by plaque enzymes to provide catabolites which cause the immediate precipitation of fluoridated calcium phosphate.

Adolescent↗
PubMed1984

The effect of fluorhydroxyapatite in experimental human dental plaque on its pH, acid production and soluble calcium, phosphate and fluoride levels following glucose challenge.

Plaque grown on terylene gauze in the mouths of 5 volunteers was treated with a mineralizing solution intermittently for 4 days to deposit fluorhydroxyapatite. Control plaque grown simultaneously was not treated. Sixteen hours after the last treatment, plaque gauzes were incubated in 0.28 M glucose under N2 at 37 degrees C. The mean pH, reached by the 5 mineralized plaques after 30 min, (4.78) was significantly higher than the mean pH reached by control plaques (4.13), a difference that was due neither to unequal microbial mass nor to unequal acid concentrations. Acid neutralization following the dissolution of apatite was probably mainly responsible for the pH differences although a small antiglycolytic effect from leached F could not be ruled out. Mineralized plaque lost on average 24 per cent of its Ca, 25 per cent of its P and 16 per cent of its F, resulting in 0.868 mM Ca, 0.676 mM P and 0.075 mM F in the supernatant. Test plaque fluid was saturated with respect to fluorapatite and only moderately undersaturated with respect to hydroxyapatite at the end of the incubation period; this could explain the pronounced caries-protective effect of plaque fluorhydroxyapatite shown previously.

Adult↗
PubMed1984

Developmental defects of enamel in a group of New Zealand children: their prevalence and some associated etiological factors.

The prevalence of developmental defects of enamel was assessed in 243 children aged 12-14 yr using the FDI Index. The teeth were not cleaned or dried prior to examination for which fibre optic lighting was used. At least one tooth with defective enamel was seen in 63% of children with a demarcated white opacity present in 44% of children. The enamel was abnormal in 11.7% of teeth, diffuse patchy opacities and demarcated white opacities occurring in 4.4 and 4.2%, respectively. Although defects were found most frequently in the maxillary central incisors, the ranking order of prevalence and the distribution for demarcated and diffuse opacities was quite different. Sex, residence, and the common childhood illnesses did not alter the prevalence of defects which was, however, increased significantly in 22 children with a history of a serious illness or accident (0.01 greater than P greater than 0.001). The prevalence of the diffuse opacities was significantly increased with increased exposure to fluoride either in tablets or in the drinking water (0.01 greater than P greater than 0.001).

Adolescent↗
PubMed1984

The ureolytic microflora of immature dental plaque before and after rinsing with a urea-based mineralizing solution.

Ureolytic bacteria were detected in the plaque flora of six subjects, and included members of the genera Actinomyces, Bifidobacterium, Staphylococcus, and Streptococcus. Proportions of these organisms did not change after subjects mouthrinsed thrice daily for four days with a plaque-mineralizing solution which contained urea and mono-fluorophosphate. The effectiveness of this rinse depends on the rapid metabolism of urea to alkali by plaque organisms, causing fluoridated apatite to precipitate in the matrix. Analysis of our data suggests that a numerically minor component of the flora, with a high turnover rate, is responsible for most of the ureolysis and the subsequent mineral precipitation.

Actinomyces↗
PubMed1983

Artificial caries produced by different oral bacterial cultures incubated with bovine dental enamel.

Early caries-like lesions were formed in enamel incubated in glucose broths inoculated with different cultures of oral bacteria. Analysis of the broths by gas chromatography revealed, after appropriate incubation, the presence of lactic, succinic, formic, acetic, propionic, isobutyric, n-butyric, isovaleric or n-caproic or mixtures of these acid catabolites. Subsurface lesions formed with all acids and mixtures providing that the terminal pH dropped less than or equal to 5.6. However, the processes conformed in part only with the idealized simple diffusion phenomenon for caries formation, indicating the presence of other factors which could affect the production of lesions in biological systems.

Animals↗