Biomedical subjects

E C Moreno

Publications and source records attributed to E C Moreno.

At least 19 recordsLinked to original sources

PubMed1994

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.

Calcium Phosphates↗

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

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↗

PubMed1992

Changes in the solubility of enamel mineral at various stages of porcine amelogenesis.

The solubility of enamel mineral (a carbonated apatite) formed at various stages of porcine amelogenesis was investigated at controlled partial pressures of CO2. Enamel samples were obtained from the outer (young) secretory, inner (old) secretory, early (soft) and late (hard) mature enamel of the permanent dentition of slaughtered piglets. The dissected enamel was pulverized and subjected to a plasma ashing at low temperature to remove organic matter. The composition (Ca, total P, HPO4, and CO3) of the enamel mineral was determined chemically. The enamel mineral contained significant amounts of carbonate and acid phosphate; the model adopted for its stoichiometry was [Ca]5-x [HPO4]v[CO3]w[PO4]3-x[OH]1-x. Each enamel sample was equilibrated in dilute phosphoric acid solutions (0.01-1.2 mM) under Pco2 = 1.86 and 1.75%. Equilibration of the enamel samples usually took 20-25 days; the solution composition (pH, concentrations of Ca, P, Mg, Na, and K, and activity of Ca2+) was determined periodically. The composition of the solution at equilibrium showed that (1) the outer (younger) secretory mineral was the most soluble and the solubility of enamel mineral decreased with advancing developmental stages; (2) the mean activity product in the saturated solutions for the outer secretory enamel was the same as that calculated on the basis of the reported composition of the enamel fluid; and (3) the solubility data obtained with most of the enamel samples were consistent with a model in which the equilibration includes two processes: dissolution of the original enamel mineral and precipitation of a new carbonatoapatite. Analyses of the equilibrated samples, particularly the mature enamel, by electron microscopy, supported the precipitation of carbonatoapatite.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelogenesis↗

PubMed1992

Competitive adsorption of magnesium and calcium ions onto synthetic and biological apatites.

Magnesium (Mg) is a conspicuous constituent of hard tissues but its possible role in biomineralization is poorly understood. It is possible that Mg2+ adsorbed onto bioapatites may contribute to the modulation of crystal growth as such inhibitory activity has been reported for synthetic apatites. The present study was undertaken to determine the adsorption isotherms of Mg ions onto synthetic apatites and biominerals in tooth and bone tissues in the presence of other ions of natural occurrence. Synthetic crystals used as adsorbents were hydroxyapatite and, as a better prototype for the biomineral, Mg-containing carbonatoapatite. Human enamel and dentin materials were obtained from extracted, caries-free, permanent teeth. Porcine dentin materials at two developmental stages were obtained from erupted deciduous and unerupted permanent teeth of a 6-month-old slaughtered piglet. Porcine bone was obtained from the cortical portion of the mandible of the same animal. All biomineral samples were pulverized and then treated by plasma ashing (deproteination) at about 60 degrees C. Each of the powdered samples was equilibrated in solutions containing various initial concentrations of Mg2+, Ca2+, and Na+ (or K+) as nitrate salts. Following equilibration, concentrations (and activities) of magnesium and calcium ions in the experimental solution were determined. The pH values of the equilibrium solutions were in the range of 6.2-6.5. Experimental data of the Mg adsorption onto hydroxyapatite were interpreted on the basis of a Langmuir-type model for binary systems assuming competition of Mg2+ and Ca2+ for the same adsorption sites on the crystal surfaces of the apatites.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗

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↗

PubMed1992

Labile or surface pools of magnesium, sodium, and potassium in developing porcine enamel mineral.

The present study was undertaken to assess the labile or surface pools of Mg, Na, and K ions in porcine enamel tissues at various developmental stages. The enamel samples, corresponding to the outer and the inner secretory, the early maturing, and the mature hard enamel, were dissected from the labial sides of permanent incisors of 6- to 8-month-old piglets. Each enamel sample was extracted successively with solutions of de-ionized water and 50 mmol/L Tris-4 mol/L guanidine buffer (for removal of organic matrix proteins, mainly amelogenins). The labile (free or organically bound) pools of Mg, Na, and K were assessed by the total amounts of these ionic species extracted by the water and Tris-guanidine buffer. The surface (adsorbed onto enamel mineral) pool of Mg was assessed directly by determination of the adsorption of Mg onto enamel mineral at various developmental stages. The results showed that: (i) 30-40% of the Mg in the secretory and early maturation enamel was in the surface pool (adsorbed onto the enamel mineral); (ii) 25 to 40% of the total sodium in the enamel samples was in labile forms; and (iii) most (around 70-80%) of the total potassium was readily extracted in water and appeared to originate from the enamel fluid; only marginal portions remained in the solids. The present adsorption studies also indicated that the maximum uptake of magnesium in the early maturation enamel was due mostly to an increase of the occupancy by Mg ions of adsorption sites on the crystal surfaces, which become accessible with a massive removal of enamel matrix proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗

PubMed1991

Morphology of the enamel organ in the miniature swine.

In recent years, the dentition of the pig has been increasingly used as a model for the study of amelogenesis. Indeed, much of our current knowledge on enamel formation derives from biochemical and physicochemical analyses of the organic and inorganic components, respectively, of porcine enamel. As an extension of this previous work, and as the first step in our attempt to correlate known enamel matrix and mineral changes with adjacent enamel organ morphology, the present study was undertaken to provide a description of the morphological events occurring in the enamel organ during porcine amelogenesis. Two-week-old miniature swine (minipigs) were fixed by vascular perfusion with glutaraldehyde, the deciduous teeth present at this age were embedded in Epon resin and sectioned, and the cells of the enamel organ at each of the various developmental stages of amelogenesis were examined by light and transmission electron microscopy. In many respects, the morphology of the porcine enamel organ was similar to that previously described in other mammalian species. On the other hand, several particularities were noted and these are discussed in the context of available data correlating cell ultrastructure with putative function during enamel formation.

Ameloblasts↗

PubMed1991

Comparative solubility study of human dental enamel, dentin, and hydroxyapatite.

The solubility properties of hydroxyapatite (HA) are compared with those of human dental enamel and dentin. The apatites used in this study were equilibrated with dilute phosphoric acid solutions in CO2-containing atmospheres. The experimental results are interpreted in terms of solubility models which consider the biological materials as either HA or carbonatoapatites. Both in the HA and the dental mineral systems, the results are consistent with the precipitation of another carbonate-containing apatitic phase during equilibration. However, although the chemical behavior of the HA systems is in very good agreement with predictions based on the solubility models, the results with the bioapatites are not; this inconsistency is more marked for dentin than for enamel but in both cases the results clearly indicate the inadequacy of assuming for these dental apatites the stoichiometry of HA. The models and the experimental results show that, in principle, it is possible to define the two dental minerals in terms of respective solubility product constants, if independent information is attained on the stoichiometry of these bioapatites.

Bicuspid↗

PubMed1991

Changes in acid-phosphate content in enamel mineral during porcine amelogenesis.

The present study was undertaken to investigate changes in the acid-phosphate content of porcine enamel mineral during its development and to assess separately the HPO4(2-) pools in labile and stable forms. Enamel samples at the secretory and maturing stages of amelogenesis were obtained from the permanent incisors of five- to six-month-old slaughtered piglets. Human enamel from erupted, extracted teeth, synthetic hydroxyapatite, and carbonatoapatite containing acid phosphate were included as references. The acid-phosphate content of each sample was determined chemically through its pyrolytic conversion to pyrophosphate. The assessment of HPO4(2-) in labile forms was made by analysis of samples preequilibrated with solutions containing 3 mmol/L phosphate at pH11 (to de-protonate the HPO4(2-) species on crystal surfaces). The analytical results of porcine enamel samples showed that: (a) the outermost secretory (youngest) enamel contained the highest HPO4(2-), corresponding to about 16% of the total phosphate; (b) the acid-phosphate content decreased gradually to 10% in the inner (older) secretory and to 6% in the maturing tissue; (c) a substantial part of the HPO4(2-) in developing enamel tissue (50-60% of the HPO4(2-) for the secretory enamel) was in labile forms; and (d) the pool of the labile HPO4(2-) decreased with the growth of enamel mineral. In parallel studies with mature human enamel, it was ascertained that the total acid phosphate was only about 3% of the total phosphate, much lower than in developing porcine enamel, and that the labile pool of HPO4(2-) was also small, corresponding to about 15% of the total acid phosphate determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Amelogenesis↗

PubMed1990

Properties of phosphorylated 32 kd nonamelogenin proteins isolated from porcine secretory enamel.

Enamel proteins were isolated from specific locations of permanent porcine incisors at various developmental stages, namely, the outer (young) and inner (old) secretory, and maturing (chalk-like in appearance) enamel. The selective adsorption of these matrix proteins onto hydroxyapatite (HA) crystals was investigated in the presence of dissociative agents. The results showed that the proteins with the highest adsorption affinity were present at the highest concentration in the vicinity of the ameloblasts, i.e., in the outer enamel layer; a substantial reduction of these proteins was observed in the older (inner) secretory enamel and in the tissue in the maturing stage. An interesting finding was that a group of proteins having molecular masses of 32 kd present only in the inner secretory enamel, adsorbed strongly onto the HA crystals and were potent inhibitors of HA crystal growth. This 32 kd group contains phosphorylated glycoproteins; they are rich in Pro, Glu, Gly, and Asp and the N-terminal sequence was LXQVPGRIPPGYGRPPTP-, having no resemblance to the reported sequences of amelogenins. It was also found that the 32 kd moieties remained only as trace constituents in the maturing enamel, suggesting that most of them were removed as soluble constituents in the tissue fluid or further degraded by enzymatic activity during the late secretory stage. The results obtained support the view that amelogenetic mineralization is regulated by the presence of various organic matter and, importantly, that their efficacy as inhibitors of mineralization may be modulated through their degradation.

Amelogenesis↗

PubMed1990

Changes in the nature and composition of enamel mineral during porcine amelogenesis.

The present study was undertaken to investigate changes in the crystalline structure and composition of procine enamel mineral during amelogenesis. Special attention was given to the carbonate location in the forming apatite crystal. Enamel samples were obtained from the outer (young) secretory, inner (old) secretory, maturation, and mature (hard) enamel of the permanent incisors of slaughtered piglets. The crystalline structure and composition of these enamel samples were studied using Fourier transform infrared spectroscopy, X-ray diffraction, and chemical analyses. The initial enamel mineral in the outer secretory enamel was rich in acid phosphate and carbonate. The carbonate was mainly substituted for phosphate groups in the apatite crystals of the early (outer) secretory enamel. Developmental advancement from the outer secretory to the inner secretory (as well as early maturation) stages brought about significant changes in crystal parameters, namely, shrinkage and expansion of the c and a unit cell dimensions, respectively, and the shift of a v3 PO4 band to higher wavenumbers in the FTIR spectrum. X-ray diffraction patterns indicated that mineralization during the tissue maturation was characterized by a gradual growth of enamel crystals parallel to the a-axis direction. A most prominent finding was that, with developmental advancement, a decrease in CO3 per unit mass of P (or Ca) in the tissue, and a concomitant increase in the CO3 occupying OH sites in the crystalline lattice became apparent.

Ameloblasts↗

PubMed1990

Effects of fluoride on matrix proteins and their properties in rat secretory enamel.

This publication concerns the selective adsorption of rat enamel proteins onto hydroxyapatite, their solubility in aqueous solutions, and the effect that systemic fluoride has on these properties. The enamel proteins used as adsorbates were extracted in 0.5 mol/L acetic acid from the secretory enamel of the upper and lower incisors of SD rats (females, 200-220 g body weight). Equilibration of the proteins with hydroxyapatite was performed in two solutions: (i) 50 mmol/L acetate buffer at pH 6.0 and 0 degrees C, and (ii) 50 mmol/L Tris buffer containing 4 mol/L guanidine at pH 7.4 and room temperature. Enamel was dissected from animals, which were given either de-ionized water (control group) or water containing 25, 50, 75, or 100 ppm fluoride as NaF for four weeks. From these enamel samples, the proteins were extracted in sequence with 160 mmol/L NaCl and 3 mmol/L phosphate (pH 7.3), 50 mmol/L carbonate buffer (pH 10.8), and finally, with 0.5 mol/L acetic acid for dissolution of the enamel mineral. The F, Ca, and P contents of the various enamel samples were determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗

PubMed1990

Effect of solution composition on morphological and structural features of carbonated calcium apatites.

The composition of enamel mineral corresponds to that of a calcium carbonato-apatite. For insight to be gained into the precipitation of carbonato-apatites having specific properties (crystal size, morphology, and carbonate incorporation into the crystal lattice), apatites were prepared at 80 degrees C in aqueous systems having various CO3 concentrations and pH values of around 7.5 or 10.5 (+/- 0.5). The various preparations had a wide range (0.005 to 0.19) of CO3/Ca molar ratios that bracket the ratios found in porcine enamel mineral at various developmental stages. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction analyses showed that the calcium apatites precipitating at neutral pH incorporated the carbonate into both the hydroxyl and phosphate ion sites in their lattices (A,B-types), whereas the preparations made at the alkaline pH (high OH-(-)CO3(2-)-competition) or in the presence of fluoride (F-(-)CO3(2-) competition) yielded only the B-type carbonato-apatite. It was also ascertained that the size and morphology of the carbonato-apatites, assessed by specific surface area determination and high-resolution electron microscopy, were highly dependent on the driving force for precipitation and the presence of regulators (CO3(2-) and F-) in solution. In neutral media, early precipitates were thin-ribbon in appearance, but grew into crystals having flattened-hexagonal cross-sections. In the presence of fluoride or in alkaline media, acicular apatite crystals, precipitated initially, grew into large rod-like carbonato-apatites having a symmetric-hexagonal cross-section. In both neutral and alkaline solutions, carbonate inhibited the growth of apatite crystals along their c axis, leading to the formation of bulkier crystals. The formation of carbonato-apatites at the neutral pH and their properties are consistent with observations made on enamel minerals formed in the early developmental stages.

Apatites↗

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↗

PubMed1990

Solubility of human enamel mineral.

The solubility of human enamel was investigated in dilute phosphoric acid solutions (0.07 mMols/L to 1.54 mMols/L) under controlled partial pressures of CO2 (0.005% to 3.33% in mixtures with N2) at 25 degrees C. The enamel mineral was considered as carbonatoapatite containing acid phosphate having the stoichiometry [Ca]5-x-y[HPO4]v[PO4]3-x[CO3]w[OH]l-x-y. During equilibration, a second apatitic phase precipitated, as observed under the electronmicroscope. Solubility models are advanced consistent with the adapted stoichiometry and the precipitation of the second phase. The latter appears to have a carbonate content similar to that of the enamel mineral even when precipitated under the lowest partial pressure of CO2, suggesting that a molar content of about 0.3 of carbonate stabilizes the apatitic lattice. Based on the adopted stoichiometry of enamel mineral, Ca4.34 (HPO4).08 (CO3).29 (PO4)2.63 (OH).05, its solubility product constant was calculated as Ksp = 1.74 (+/- 0.081)x10(-6), expressed as the mean activity product.

Calcium↗

PubMed1990

Molecular conformation of porcine amelogenins and its significance in protein-mineral interaction: 1H-NMR photo-CIDNP study.

The present 1H-nmr study was undertaken to investigate the molecular structure of porcine amelogenins in solution using photo-CIDNP (chemically induced dynamic nuclear polarization). The proteins of interest were the parent 25 kD amelogenin consisting of 173 amino acid residues and its degraded products having molecular masses of 23 kD, 20 kD, 13 kD and 5 kD on SDS-PAGE. From the recorded 1H-nmr and photo-CIDNP spectra, it was found that: 1) the Trp161 at the C-terminus of the 25 kD protein showed a stronger photo-CIDNP effect than the other two Trp25,45 at the N-terminus; 2) Tyr residues at the N-terminus of the 25 kD and 20 kD amelogenins gave rise to the strong peak around 6.8 ppm, indicating that at least some of the six Tyr residues are surface residues; and 3) the accessibility of His residues was quite different between the 13 kD fragment and the 25 kD and 20 kD proteins. These results suggest that the hydrophilic segment at the C-terminus is most likely exposed on the molecular surface and that the molecular structure of the amelogenin in solution may change substantially by the cleavage of the segments at the N- and C-termini.

Amelogenin↗