Biomedical subjects

E I Pearce

Publications and source records attributed to E I Pearce.

At least 37 records · Page 2Linked to original sources

PubMed1995

The effect of fluorhydroxyapatite-derived fluoride on acid production by streptococci.

The effect of fluoride derived from fluorhydroxyapatite (FHAp) minerals on bacterial glycolysis under aerobic and strictly anaerobic conditions was studied to validate the claims that this mineral could be used as a reservoir of fluoride in plaque. To isolate the direct effect of fluoride on bacterial glycolysis from that of an indirect pH-buffering effect of hydroxyl or phosphate ions which are also dissolved from the mineral, we equalized the pH-fall time course of reactions by manually adding KOH or HCl. This ensured that pH effects on glycolysis were minimized. Under controlled pH-fall and strictly anaerobic conditions, fluoride derived from the dissolution of FHAp containing more than 30,100 ppm fluoride (i.e., when the substitution of OH by F in the mineral was greater than 80%) had a direct inhibitory effect on lactic acid production in Streptococcus mutans. Under free pH-fall and strictly anaerobic conditions, increasing amounts of fluoride in FHAp (starting as low as 2000 ppm fluoride), appeared to have a pronounced indirect inhibitory effect on lactic acid production. This was probably mediated through a reducing pH buffer effect of the mineral. Even in the presence of high-fluoride FHAp, only 0.01 to 0.025 mmol/L fluoride was found in the reaction mixtures, a probable result of non-stoichiometric dissolution of FHAp. In spite of such low levels of fluoride, marked inhibitory effects on bacterial glycolysis were demonstrated. The results of this study suggest that high-fluoride FHAp may serve as a reservoir of fluoride for the inhibition of anaerobic acid production by S. mutans.

Anaerobiosis↗

PubMed1995

The distribution of fluoride in carious human enamel.

The proton probe has been used to map F concentration changes in the enamel of 15 teeth showing clinical evidence of caries. Thin sections through the lesions were microradiographed and measurements made of the surface zone (radiodense) and body (radiolucent) areas. Each section was then scanned with a focused beam of 2.5 MeV protons, 2000 spot analyses being performed over areas up to 2 x 3 mm. F was determined by detecting gamma rays from a nuclear reaction and the data used to construct 3-D surface plots. The maximum F concentration in the lesion surface zone was extremely variable, ranging from 1750 to 21,700 ppm, and rarely occurred over the deepest part of the lesion. F levels were elevated in the lesion body but usually to a small extent only. A large increase in F throughout the lesion body was found in 3 lesions only, and was associated with a surface zone that was thin or of low x-ray density. Relatively small F increases in the lesion body were associated with either a thick, x-ray dense surface layer having a greatly increased F level (> 10,000 ppm) or, conversely, with a surface layer having a relatively small F increase. Since F uptake can be regarded as a "marker" of past remineralization events, this study shows that remineralization can and does occur in the body of natural enamel caries lesions, especially when the surface layer is thin or lost. Fluoride availability that encourages the formation of an extremely dense surface layer may result in under-achievement of this natural repair process in the lesion body.

Dental Caries↗

PubMed1995

Effects of fluoride-supplemented sucrose on experimental dental caries and dental plaque pH.

Sucrose, 5% and 10% (w/v), supplemented with between 0 and 5 ppm fluoride (F), was tested for its influence in vitro on plaque-induced experimental in vitro enamel caries and plaque pH. Plaque growth on bovine enamel was initiated from saliva inocula and sustained in a multiple plaque growth system for up to 31 days by means of a basal medium with periodic applications of sucrose or sucrose supplemented with F. Change in enamel mineralization was assessed, before and after plaque growth, by microhardness testing and microradiography; pH was monitored with microelectrodes. It was found that enamel demineralization was inversely related to the F concentration in the range 2 to 5 ppm, for both 5% and 10% sucrose. Plaque pH responses were unaffected by the F supplements.

Analysis of Variance↗

PubMed1994

The effectiveness of bone char in the defluoridation of water in relation to its crystallinity, carbon content and dissolution pattern.

The procedure for charring bone has been found to influence the nature of its mineral phase, and also affects the defluoridation capacity of the char. The aim of this study was to examine the efficiency of defluoridation by char produced from various parts of bones and charred for various lengths of time at various temperatures, relating the preparation of the char to its X-ray diffraction pattern, its content of pyrophosphate and its capacity for defluoridation. Bone was charred for 1 and 4 h at 400 degrees C and 30 min, 4 h and 48 h at 550 degrees C. Batches of the chars were suspended in amounts of 0.25 g in 100 ml of distilled water containing 0.53 mmol/l fluoride for up to 6 days under gentle agitation. At intervals, the pH and concentrations of fluoride, calcium and phosphate in the water were determined and the degree of saturation with respect to the calcium phosphate salts calculated. The charring procedure reduced the organic content of the bone from the 44-26% in intact bone to 3.4% in bone charred at 400 degrees C and to almost zero when charred at 550 degrees C for 48 h. When charred at 400 degrees C for up to 4 h the X-ray diffraction pattern of the bone showed a poorly crystallized apatite similar to that of untreated bone. Heating for 48 h or more at 550 degrees C led to considerably sharper apatite reflections, indicative of a well-crystallized salt.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗

PubMed1994

The effect of mineral-derived zinc ions on in vitro glucose metabolism of Streptococcus mutans NCTC 10449.

Mouthrinses containing zinc ions inhibit plaque acidogenicity, but the effect is transient. Zinc-containing apatite or zinc phosphate precipitated within dental plaque might serve as a reservoir for zinc ions, thus providing prolonged inhibition of acid formation. Zinc-containing fluorhydroxyapatite was prepared from solutions containing CaCl2, KH2PO4, NaF and increasing amounts of ZnCl2 (0.0, 0.005, 0.02, 0.1, 0.2 or 1 mM; minerals No. 1-6, respectively) by raising the pH with ammonia. Zinc phosphate tetrahydrate (mineral No. 7) was prepared in a similar manner from a solution containing ZnCl2 and KH2PO4 only. Dense cell suspensions of Streptococcus mutans NCTC 10449 were incubated with 14C-glucose and one of the test minerals (No. 1-7). Glycolysis was allowed to proceed, with or without pH control, in a pH-stat. Samples were withdrawn at 1, 2, and 3 min, and extracellular glycolytic metabolites were identified by HPLC. Mineral No. 7 inhibited glycolysis and any pH fall almost completely. With the pH fixed at 5.5, reduction of glucose consumption and lactate formation was 83 and 93%, respectively, compared to the no-zinc control mineral (No. 1). No changes in glucose consumption or lactate formation were evident in the presence of minerals No. 2-6. All apatitic minerals had a buffering effect and, in the absence of pH control, glycolysis was increased due to the higher pH. Detectable levels of fluoride were not released by any mineral into the incubation mixture, and zinc only by minerals No. 6 and 7 in greater than trace amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗

PubMed1994

Proton probe and acid etching for determining fluoride profiles in porous porcine enamel.

An acid-etch technique and a proton probe were used to obtain profiles of changes in fluoride concentrations across enamel of 24 normal and 24 fluorotic porcine teeth. Polished and unpolished sections were used for probe measurements, and blocks of enamel cut from tissue adjacent to the sections were used for acid etching. Additional blocks were etched with acid containing dye to study penetration of acid beyond the sampling sites. Probe-derived values were characterized by wide fluctuations. They were also higher than acid-etch values, and this difference was reduced but not eliminated by polishing the sections prior to scanning. Profiles obtained with the two methods followed a parallel course in fluorotic and normal enamel. Thus, errors due to chemical estimations of enamel depth with the etch technique were not demonstrated, although penetration of acid deep to the surface of the porous fluorotic enamel was observed. Further development of the precision of the probe method is required to optimize the unique advantage provided by the potential accuracy, speed of data collection, and spatial resolution of this method.

Acid Etching, Dental↗

PubMed1993

Notes on the dissolution of human dental enamel in dilute acid solutions at high solid/solution ratio.

The aim of the present study was to elucidate the nature of the relationship between enamel apatite and lesion fluid during demineralization. Powdered enamel in samples of 1.0 g was suspended in 3 ml of 10, 30, 50, or 70 mmol/l HCl under gentle agitation for up to 24 h at 20 degrees C. After 20 min and 24 h, pH and the concentrations of calcium and phosphate were determined and the degree of saturation with respect to various calcium phosphates calculated. The experiments were replicated 15 times using the same enamel samples. Twenty minutes after the start of dissolution, both pH and concentrations of calcium and phosphate had increased, and the solution became supersaturated with respect to hydroxyapatite, and in some runs also with respect to brushite. During the subsequent 23 h and 40 min, pH continued to increase, despite the supersaturation with respect to apatite, whilst the concentrations of calcium and phosphate decreased due to formation of apatite and, occasionally, brushite mineral. The data indicated that release of carbonate from enamel and its conversion to H2CO3 caused the increase in pH and thus, played a major role in the dissolution-reprecipitation process.

Calcium↗

PubMed1993

Defluoridation of drinking water by co-precipitation with apatite.

The two-step brushite saturation, apatite precipitation method which has previously been shown to be effective for the partial defluoridation of water containing 10 ppm F has now been tested at lower concentrations. The method also reduced F concentrations in the range 1-5 ppm, but was less efficient at lower F levels. Although co-precipitation as fluorapatite is the intended mechanism here, experiments indicated that F adsorption on the seed material added to the defluoridation effect. When the contribution of co-precipitation was isolated it was found that this mechanism could, on its own, account for a reduction of 2.2-2.6 ppm F in water initially containing 3-5 ppm F. A computer program which determines equilibrium F concentrations when supersaturated solutions are induced to precipitate fluorapatite was used to estimate the maximum possible F removal from water by co-precipitation. Using saturation with brushite as a starting point for precipitation, F reductions similar to those found experimentally were predicted. Computer simulations also suggest that any desired reduction in F concentration may be achieved by adding sufficient Ca and phosphate and/or by raising the initial pH.

Adsorption↗

PubMed1993

Defluoridation of water at high pH with use of brushite, calcium hydroxide, and bone char.

The aim of this study was to improve the efficiency of the bone-char method of water defluoridation by pre-treating the water with brushite and calcium hydroxide. Various amounts of brushite, calcium hydroxide, and bone char were suspended batchwise in 100 mL of distilled water containing 0.53 mmol/L fluoride for 24 h under gentle agitation. At suitable intervals, pH and the concentrations of fluoride, calcium, and phosphate in the water were determined and, when possible, the degrees of saturation with respect to brushite, hydroxyapatite, and fluorapatite calculated. Bone char used alone took up fluoride slowly and inefficiently. The addition of brushite and calcium hydroxide resulted in high concentrations of calcium and phosphate, making the solutions highly supersaturated with respect to fluorapatite, and led to a 20-fold increase in fluoride removal from the water. The combined use of all three salts left low concentrations of phosphate in solution and optimized the fluoride uptake capacity. Repeated use of the same bone char for 18 consecutive runs demonstrated that uptake of fluoride by the bone char was improved by repeated use, provided that brushite and calcium hydroxide were added. Therefore, addition of the two salts to the water may prolong the life of the bone char indefinitely, ensure the removal of fluoride, and thus avoid the problem of determining when the bone char is exhausted. In conclusion, we show that the bone-char defluoridation technique can be improved by addition of brushite and calcium hydroxide to the water. The problem of high terminal pH remains, however, and further work is required to improve potability.

Animals↗

PubMed1992

Some notes on the diffusion of acidic and alkaline agents into natural human caries lesions in vitro.

The aim was to obtain information on the penetration of ions, in particular H+ and OH-, into a wide variety of natural caries lesions in human teeth. Thirty-seven permanent teeth were slit in half and soaked in a 1% neutral (blue) litmus solution for at least a week. The cut face of the tooth was painted with a transparent, colourless nail varnish before the tooth was immersed in either of 0.1 M hydrochloric acid or 0.1 M phosphoric acid. In a reverse experiment the samples were soaked in acid (red) litmus solution and then immersed in 0.1 M sodium hydroxide after varnishing the cut face. All solutions were saturated with enamel apatite to avoid the possibility that the solutions might etch their way into the enamel. The colour change was recorded photographically. Several days of external acid/alkali exposure were required to change the litmus colour in the body of most of the lesions, suggesting that diffusion of acidic and alkaline species through the natural surface into the body was slow. The presence of a well-mineralized surface layer covering the lesion postponed the colour change. In contrast, the colour change of two root surface lesions was rapid, occurring within an hour. Thus, because the lesion body is relatively isolated and because lesion fluid is in intimate contact with the enamel apatite, we conclude that lesion fluid is close to saturation with respect to this mineral. Further, a pH change of lesion fluid in vivo paralleling that in plaque after a sucrose intake is unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Caries↗

PubMed1992

Partial defluoridation of drinking water using fluorapatite precipitation.

Ion adsorption and ion exchange are two methods commonly used in small home units to treat drinking water to bring the fluoride concentration to within acceptable limits. However, the necessary flowthrough system is often difficult to arrange where there is no piped supply and gradual exhaustion of the active agent is not easily detected. In an attempt to overcome these problems a defluoridation method based on the precipitation of a sparingly soluble fluoride salt, fluorapatite, has been studied. Samples of simulated high-fluoride drinking waters, approximately 10 ppm F, were saturated with brushite, resulting in a state of supersaturation with respect to fluorapatite. Subsequent seeding with hydroxyapatite caused a lowering of the calcium, phosphate, and fluoride concentrations in solution, indicative of fluorapatite precipitation. Repeating the process had an additive effect. Bone char was a less effective seed than hydroxyapatite with water containing fluoride only, but was a more effective seed with simulated Kenyan borehole water containing additional salts. Sixty-minute brushite saturation and apatite seeding steps were generally more effective than 10-min steps. The results suggest that apatite coprecipitation may be a convenient low-technology way to defluoridate drinking water, although prior testing might be useful to ensure adequate removal of fluoride.

Apatites↗

PubMed1992

Supplementation of domestic sugar (sucrose) with fluoride. Effects on experimental dental caries, plaque pH, and fluoride levels in plaque and enamel.

The minimum amount of fluoride which, when added to sucrose, will reduce caries in an intra-oral test was determined. Removable lower-arch appliances were worn by three adult subjects for 1 week, during which time plaque-covered enamel on one side was immersed in a 10 percent sucrose solution containing fluoride for 10 minutes four times per day. The effect of sucrose alone (control) was similarly determined on the other side of the appliance. Concentrations of 2 and 5 ppm F in sucrose solutions (20 and 50 ppm F dry weight) produced highly significant reductions in experimental caries of 43 and 44 percent respectively. A reduction in enamel dissolution due to re-precipitation of fluoride-rich apatite is probably largely responsible for the anti-caries effect. However, decreased plaque acid production may also play a role since the addition of 1 ppm F to 5 percent sugar reduced the plaque pH drop in artificial mouth experiments. Our results substantiate previous reports that fluoridation of sucrose to a level of 20 to 50 ppm F dry weight has potential benefits in caries prevention and may be useful when the F intake is otherwise low.

Adult↗

PubMed1991

Therapeutic mineral enrichment of dental plaque visualized by transmission electron microscopy.

The form, location, and distribution of fluorhydroxyapatite deposited in dental plaque by a urease-mediated mineral enrichment process have been studied by transmission electron microscopy. Artificial plaque was formed in terylene gauze in the mouth of one subject and immersed for five min four times per day in a mineral-enriching solution. Contralateral control plaque remained untreated. The effect on natural plaque was studied in two subjects who withheld oral hygiene for four days and mouthrinsed with this solution for two min four times per day during the last two days. Mineral deposits were seen in all plaque samples exposed to the test solution. None was detected in any control sample. The deposits were scattered in the interbacterial matrix as needle-shaped crystals, the size and shape of apatite, together with amorphous material. The crystals appeared larger and more perfect, and the amorphous material less conspicuous, with longer in vivo rinsing periods. Platelet-shaped crystals of octacalcium phosphate were never seen. Mineral was also seen within the remnants of dead bacterial cells and within degenerating epithelial cells. Crystals were never seen within intact bacterial cells, as in calculus formation. The presence of a single crystal type and the relative absence of densely-mineralized foci are other differences between this mineral-enrichment process and supra-gingival calculus formation. A longer-term study is necessary to determine whether the solution promotes calculus by providing nucleation seeds.

Calcium Chloride↗

PubMed1991

Relationship between demineralization events in dental enamel and the pH and mineral content of plaque.

Acid production in dental plaque from fermentation of dietary carbohydrate does not necessarily lead to demineralization of the underlying enamel. In the past it has been understood that pH buffering by plaque constituents must be overcome to allow the pH to fall, and then the fall must be of sufficient magnitude to exceed a critical pH value, i.e. the point where plaque fluid is just saturated with respect to enamel mineral. An evaluation of the literature suggests, however, that the critical pH is not a fixed value. It changes slowly as enamel mineral solubility changes with repeated pH cycling. Further, plaque mineral ion sinks, in which ions are removed from solution (first described by Luoma in 1964) and ion reservoirs from which ions are added to solution, modulate the critical pH value during plaque pH fall and rise so that its exact value is difficult to predetermine. A solid phase calcium phosphate ion reservoir in plaque may saturate plaque fluid with respect to enamel mineral continuously as the pH falls so that the critical pH is never exceeded. Common ion repression of enamel mineral dissolution is likely to be effective in the order pH greater than Ca greater than P. Plaque fluoride influences enamel dissolution in more than one way. Simultaneous dissolution of hydroxyapatite and reprecipitation of fluorapatite, a process which results in apparent dissolution repression, is probably the most important mechanism initially. This process may coat individual enamel crystals with a F-rich layer so that, while the total F content is rather low, its effective solubility is more like that of fluorapatite. Fluoride in plaque fluid may then repress enamel mineral dissolution by common ion repression. If fluoride action follows this sequence efforts to build F into enamel clinically would be just as important as attempts to maintain F levels in plaque and saliva.

Dental Enamel↗

PubMed1990

Effect of monofluorophosphate on calcium phosphate formation in supersaturated solutions.

The effect of purified monofluorophosphate (MFP) on the formation of hydroxyapatite (HA) in supersaturated calcium phosphate solutions was determined. In solutions initially at pH 7.4 and seeded with HA crystals, MFP was hydrolysed to a small extent, releasing F-. Once the crystal growth-enhancing property of this F- was compensated for, 4 mmol/l MFP could be shown to inhibit precipitation by 40%. Without compensation for F-, MFP appeared to inhibit precipitation by only 18%. This inhibition was weaker than that caused by pyrophosphate or ethane-1-hydroxy-1,1-diphosphonic acid. Because MFP is hydrolysed on apatite surfaces to F-, use of sodium MFP as an anticaries agent is unlikely to cause significant inhibition of enamel remineralization.

Calcium↗

PubMed1989

A comparison of the cariogenicity of two infant snack foods.

Two snack foods marketed specifically for infants were compared in caries prediction tests. A milk powder-supplemented fruit and cereal snack bar produced more titratable acid but did not reach as low a terminal pH as a sweet biscuit on in vitro fermentation by salivary organisms. In an intra-oral caries test the fruit/cereal bar caused significantly less enamel softening than the biscuit. While this latter test does not assess food retention in the mouth and other factors important in caries, the results suggest that, under similar usage by children, the fruit bar will be less cariogenic. Because it was not absolutely safe with respect to caries, frequency of eating cannot be disregarded. Availability of the fruit snack bar is an important development, allowing an additional choice for parents who wish to select low-cariogenicity foods for their children.

Adolescent↗

PubMed1989

Microstructural features of carious human enamel imaged with back-scattered electrons.

We have used back-scattered electrons (BE) in the scanning electron microscope to produce mineral density images of enamel. Flat surfaces of artificially-carious enamel, softened in an intra-oral experiment, and naturally-carious (white spot) enamel were polished to a high gloss with diamond lapping compound, rendering them almost featureless by secondary electron scanning electron microscopy. They were then examined at 10 to 30 kV in a Philips 505 instrument fitted with a 4-quadrant BE detector. Study of surfaces prepared approximately parallel to the natural surface showed that mineral was lost from both prism core and the interprismatic region, leaving a thin mineral-rich rim at the prism periphery. The same lesions viewed longitudinally on a surface prepared perpendicular to the natural surface showed mineral-rich bands at the prism margins in the outer enamel. Near the advancing front of the lesion, the prism junctions were widened and the prism cores sometimes hypermineralized. Natural lesions sectioned in the prism long axis showed features previously seen with other techniques, e.g., cross-striations and striae of Retzius, but in much greater detail. Mineral enrichment at the prism periphery in the lesion body and a widening of the prism junction at the advancing fronts of lesions in permanent teeth were most obvious. Calculations showed that with an accelerating voltage of 30 kV, the images reflected mineral density up to 4 microns beneath the surface. BE microscopy produces a high-resolution image of mineral loss or gain in carious enamel, with relatively easy sample preparation.

Dental Caries↗

PubMed1988

In vivo comparison of caries inhibition by a plaque mineral enriching mouthrinse and a fluoride dentifrice.

Six subjects wore lower-arch intra-oral appliances supporting plaque-covered enamel units in the left and right buccal sulci. Units on both sides received identical cariogenic challenges by intermittent immersion in 0.28 M glucose. When one side was treated, in addition, with a mouthrinse designed to enrich plaque with Ca, P, and F, there was a 76% reduction in the softening and a 96% reduction in the porosity, created in enamel by the glucose exposures. F dentifrice extract, used similarly, caused a 67% reduction in enamel softening and a 93% reduction in porosity. When the two treatments were compared in the same experiment, the mouthrinse had a significantly greater effect in limiting enamel softening, but the porosity measurement technique was not sensitive enough to confirm this finding. Use of the mouthrinse caused variable deposition of fluorhydroxyapatite in plaque, and scanning electron microscopy examination of enamel showed small adherent hard deposits in some subjects. The polished enamel surface enabled backscattered electron imaging which revealed preferential dissolution of the core and tail regions of the prism. The results suggest that plaque mineral enrichment may be even more effective than F dentifrice in preventing dental caries.

Adult↗