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Biomedical subjects

J C Voegel

Publications and source records attributed to J C Voegel.

At least 19 recordsLinked to original sources
PubMed1992

Competitive adsorption of human immunoglobulin G and albumin: consequences for structure and reactivity of the adsorbed layer.

The affinity of polyclonal anti-IgG for human IgG adsorbed on silica surfaces was investigated by two complementary techniques, scanning angle reflectometry and 125I radiotracing. Special attention was paid to compare the reactivity of IgG adsorbed directly or by exchange with already adsorbed albumin. In particular it was shown that (i) in the first case (direct adsorption) the reaction between anti-IgG and adsorbed IgG was in the ratio 1:1 and (ii) in the second case (adsorption by exchange) there was no reaction.

Adsorption↗
PubMed1992

Human amelogenesis. I: High resolution electron microscopy study of ribbon-like crystals.

Ribbon-like crystals, from developing enamel of human fetuses, were studied by high resolution electron microscopy. These crystals were classically described as the first organized mineral formed during amelogenesis. They were characterized by a mean width-to-thickness ratio (W.T-1) of 9.5, and 40% were bent. On lattice images we noted the presence of the central dark line (CDL) associated with white spots. Both structures were found in crystals with a minimum thickness of 8-10 nm. CDLs were localized in the center of the crystals and seemed to be linked to the initial growth process, but their exact structure and function were not fully determined. We were able to study the structure of the ribbon-like crystals with a Scherzer resolution close to 0.2 nm. The good correspondence between experimental and computed images showed that their structure was related to hydroxyapatite (HA). In addition, the presence of ionic substitutions and deficiencies were also compatible with HA. In this study, about 50% of the crystals showed structural defects. Screw dislocations were the most often noted defects and were observed within crystals aligned along five different zone axes. Low- and high-angle boundaries were also detected. Low-angle boundaries, found in the center of the crystals, could thus be related to CDLs and be implicated in the nucleation step of crystal formation, whereas high-angle boundaries could result from the fusion of ribbon-like crystals. Such mechanisms could induce an acceleration of the growth in thickness of the crystal observed during the maturation stage of amelogenesis.

Amelogenesis↗
PubMed1992

Effects of carbon dioxide, Nd:YAG and carbon dioxide-Nd:YAG combination lasers at high energy densities on synthetic hydroxyaptite.

The aim of this study was to determine the crystalline structure and chemical alterations of synthetic hydroxyapatite after irradiation with either CO2, Nd:YAG or CO2-Nd:YAG combination lasers at high energy densities of 500-3,230 J.cm2. Further, dissolution kinetics of the lased material were analysed and compared with those of unlased apatite. Electron microscopy showed that the lased material consisted of two kinds of crystals. From the micrographs their diameters varied from 600 to 1,200 A and from 3,000 to 6,000 A, respectively. The larger crystals showed 6.9-Angström periodic lattice fringes in the transmission electron microscope. alpha-Tricalcium phosphate (TCP) was identified by X-ray diffraction. Selective-area electron diffraction identified the large crystals to consist of tricalcium phosphate while the smaller crystals were probably hydroxyapatite. Assays of dissolution kinetics showed that at these high energy densities lased material dissolved more rapidly than unlased synthetic hydroxyapatite due to the higher solubility of TCP.

Aluminum Silicates↗
PubMed1992

Urinary fluoride excretion in children using potassium fluoride containing salt or sodium fluoride supplements.

With the introduction of fluoridated domestic salt in France in 1986, questions have arisen with respect to its efficacy in caries prevention. It has been of interest to compare the urinary excretion of fluoride in children who consume fluoridated salt to that in children who take fluoride tablets. Ninety-three schoolchildren, 10-14 years of age, participated in the study and were divided into four groups: group I consumed fluoridated salt with every meal; group II ate at a school restaurant once a day and consequently consumed fluoridated salt at only their evening meal, as fluoridated salt is not authorized for use in collective restaurants; group III consisted of children taking fluoride tablets (1.0 mg F/day) exclusively, and group IV did not receive any systemic administration of fluoride for prevention and constituted a low-fluoride control group. Total 24-hour urine samples were collected from all subjects. The average daily urinary flow rates varied from 0.51 to 0.68 ml/min, but showed no statistically significant differences among the groups. The average urinary fluoride concentrations were 0.60, 0.30, 0.99, and 0.28 mg/l, respectively, for groups I-IV. The mean 24-hour urinary fluoride concentrations and excretion rates for children who consumed fluoridated salt at all meals (group I) were not statistically different from those using tables (group III). There were also no statistically significant differences between groups II and IV. The differences between urinary fluoride concentrations and excretion rates of groups I and III, as compared with group IV, were statistically significant.

Administration, Oral↗
PubMed1992

Critical analysis of an experimental set-up generally used for the permeability evaluation of dental lining material.

The diffusion constants of iodide through dentine membranes were determined. The DI-values were within the range generally obtained by other investigators. When the estimation of the diffusion coefficient through a well defined polycarbonate membrane was calculated the value was strongly affected by the diffusion through the unstirred diffusion layer. By using such an experimental approach it seems necessary to develop a new cell equipped with a double stirring system (one in each compartment) in order to reduce strongly the thickness of the unstirred diffusion layer.

Dental Cavity Lining↗
PubMed1991

Adsorption/desorption of human serum albumin on hydroxyapatite: a critical analysis of the Langmuir model.

We studied the adsorption of human albumin onto synthetic hydroxyapatite, using a radiotracer technique and a special flow cell. Adsorption was studied under various conditions corresponding to different thermodynamic paths. It appears that (i) as is the usual case, the isotherms obtained within a short time range (a few hours) do not correspond to a true equilibrium situation; (ii) when the adsorption process is followed for longer times, which is necessary at low bulk concentrations, one always reaches the plateau surface adsorption; (iii) this plateau value is independent of the "history" of the adsorption process and corresponds well to the jamming limit predicted by the random sequential adsorption model; and (iv) surface denaturation, leading to enhanced surface binding and thus decreasing desorption constants, is the important phenomenon that can partly and qualitatively explain our observations. Its time dependence, however, remains to be clarified.

Adsorption↗
PubMed1991

HREM study of irradiation damage in human dental enamel crystals.

Several phenomena have been observed during the examination of human dental enamel crystals (mainly constituted by hydroxyapatite (OHAP] by high-resolution electron microscopy (HREM) at 300 and 400 keV: orientation-dependent damage in the form of mass loss from voids or uniform destruction of crystal structure, beam-induced diffusion creating outgrowths at the crystal surfaces, recrystallization of the bulk crystal and crystallization of the inorganic components of the matrix surrounding the crystals. These beam-induced crystals have the CaO structure. The phenomena observed are most likely due to various electron-crystal interaction mechanisms (ballistic knock-on damage, electronic excitations, temperature rise, etc.). In this paper, the contribution of the ballistic process to the phenomena observed is discussed. The quantitative description of the knock-on collisions rests on the McKinley-Feshbach cross-section formula. The minimum ion displacement energies which appear in this expression have been estimated on the basis of the electrostatic ion binding energies, and the covalent bond energies if required. It is shown that hydroxyl, calcium and oxygen ions can effectively be displaced by the incident 300 and 400 keV electrons. Thus, the formation of CaO crystals by the combination of calcium and oxygen ions diffusing from their initial sites inside the OHAP lattice can tentatively be explained.

Adult↗
PubMed1991

Compositional variations in apatites with respect to preferential ionic extraction.

Detection of ionic losses from the apatitic structure (Ca10(PO4)6(OH)2) by high-resolution electron microscopy was investigated theoretically. Linear image analysis showed the need for an objective aperture of at least 3.7 nm-1 to visualize four different coordinates (CaII, OH-, P and mid-point between CaII-P bond). High-resolution image analysis and plotting of OH- column intensity against specimen thickness showed an inverse proportionality between composition and OH- image intensities for very thin specimens (less than 2 nm). Image intensity variation would be detectable experimentally, but the preparation of such thin specimens by ultramicrotomy is impossible.

Apatites↗
PubMed1990

Exposure to mercury vapor during setting, removing, and polishing amalgam restorations.

The level of mercury vapors in the oral cavity was determined by analyzing 242 samples of intra-oral air before and after removing, setting, and polishing dental amalgam. The analysis was effected using atomic absorption spectrometry in cold vapors with the detection limit of 6 micrograms/m3. A score of 1 to 3 was assigned to each restoration to adjust the differences of the amalgam sizes. The present study showed that the vapor was released during any procedure: removing, setting, and polishing amalgam. The mean levels were between 85 and 326 micrograms/m3. However, before the restorative procedures, no mercury vapors had been detected in the oral cavity. This investigation has also demonstrated a significant direct correlation between Hg vapor concentrations in intra-oral air and the sizes of amalgam restorations during each procedure: removing, setting, and polishing. The statistic analysis showed no significant difference of mercury vapors in the oral cavity between the use or nonuse of water coolant during the amalgam polishing.

Air↗
PubMed1990

Kinetics of dissolution of calcium hydroxyapatite powder. III: pH and sample conditioning effects.

The kinetics of dissolution of synthetic hydroxyapatite powder (HAP) were studied at 37 degrees C and constant pH in the pH range 3.7-6.9 by continuously recording proton uptake and calcium release. The effect of sample conditioning was carefully investigated. The powder previously equilibrated in saturated solutions shows an initial dissolution rate higher than the one obtained when dry powder directly added to the dissolution solution is used. This effect is interpreted by considering surface state differences. As previously shown, dry powder contains important amounts of calcium and phosphate ions adsorbed onto apatite surface, ions which are desorbed during equilibration. It is assumed that the initial presence of these ions slows the dissolution rate during the first stage of the process by the formation of a permselective layer. Except for these adsorption phenomena which are less important for human enamel powder (HEP) having a lower specific surface area, it is shown that in spite of structural, morphological, and purity differences, the general dissolution behavior of HAP is quite similar to that of HEP, previously studied, and for which a quantitative model has been proposed. The dissolution rates are stirring dependent in a large range of stirring speeds and are proportional to [H+]0.64. Moreover, it is shown that in the whole range of studied pH, a calcium accumulation process occurs at the interface during the first minutes of the acidic attack. It is concluded that in our experimental conditions, the dissolution process is limited by the diffusion of calcium and/or phosphate ions in the interface.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1990

Development of an automated experimental setup for the study of ionic-exchange kinetics. Application to the ionic adsorption, equilibrium attainment and dissolution of apatite compounds.

An ion-selective electrode and microcomputer-based experimental setup for the study of ionic-exchange kinetics between a powdered solid and the solution is described. The equipment is composed of easily available commercial devices and a data acquisition and regularization computer program is presented. The system, especially developed to investigate the ionic adsorption, equilibrium attainment and dissolution of hard mineralized tissues, provides good reliable results by taking into account the volume changes of the reacting solution and the electrode behaviour under different experimental conditions, and by avoiding carbonation of the solution. A second computer program, using the regularized data and the experimental parameters, calculates the quantities of protons consumed and calcium released in the case of equilibrium attainment and dissolution of apatite-like compounds. Finally, typical examples of ion-exchange and dissolution kinetics under constant pH of enamel and synthetic hydroxyapatite are examined.

Adsorption↗
PubMed1990

High-resolution electron microscopy of human enamel crystals.

The structure of enamel crystals obtained from four human premolars has been studied by high-resolution electron microscopy (HREM) in the [0001], [2110], [1540], [0110] and [1213] crystallographic directions at various microscope defocus and crystal thickness values. The resolution obtained has not previously been reported for human enamel crystals. In all cases, it was possible to match the experimental images to images calculated using the atomic positions of mineral hydroxyapatite. However, a deviation from hexagonal symmetry characterized by marked (1010) planes of intensity different from the one of the (3030) and (1010)-type planes was observed. In this work, we present an improvement of Scherzer resolution of 0.25-0.20 nm over previous work on biological enamel crystals. This improvement of resolution has permitted the incorporation of crystallographic reflections of higher spatial frequencies into the imaging process of the microscope and has led to a more precise structure determination of the crystals studied.

Adult↗
PubMed1990

High resolution electron microscopy of young apatite crystals in human fetal enamel.

Apatite crystal growth in enamel has been followed during the secretory stage in 5 month-old human fetuses. The crystals were observed in a high resolution transmission electron microscope operating at 300 kV. This microscope has a Scherzer resolution of 0.19 nm and for each micrograph, the absence of astigmatism and drift was checked with optical diffractograms. Crystals in various stages of growth from approximately 3 to 10 unit cells in thickness could be observed along [0001] and mean value of 1010 zone axes. For growing crystals, a highly ordered atomic structure with an ionic distribution consistent with hydroxyapatite was noted as demonstrated by the correspondence of computer simulated and observed images. Moreover, most of the crystals showed structural defects such as edge dislocations and periodically repeated strain fields created by screw dislocations. The observed dislocations were described by Burgers vectors running parallel to mean value of 1120 axes.

Computer Simulation↗
PubMed1989

Desorption and exchange properties of adsorbed albumin on apatite. Influence of long-term interfacial residence times.

A technique using 125I-labeled proteins was employed to study static adsorption properties and slow exchange and desorption processes of human albumin in contact with synthetic hydroxyapatite beads. With the aid of a thermostated "minicolumn," the adsorption isotherm was obtained during a so-called multiadsorption process, and could be described by a Langmuir adsorption model (K = 1.10 x 10(10) cm3.mol-1). All kinetic desorption and exchange experiments could be fitted by a simple exponential function of time. No influence of long-term interfacial residence times on characteristic relaxation times or percentage of desorbed or exchanged proteins could be detected in the present system. On the other hand, as compared to the low surface coverage domain, the small percentage of desorbable and high percentage of exchangeable molecules in the adsorption plateau domain was attributed to a bimolecular exchange process.

Adsorption↗
PubMed1979

Biological apatite crystal disolution.

The dissolution curves of human acid-treated enamel powder are characterized by a rapid initial step followed, after 10 or 15 minutes, by a second stage, with release of very small amounts of calcium. Increase in pH and addition of fluoride ions tend to diminish, for short intervals, the amount of dissolved apatites. For higher pH values the decrease is noted over a longer time. Study of the relative ionic variation of human enamel powder from young and adult patients subjected to acid requires infra-red vibration band analyses. Special attention was given to the absorptions at 610 cm-1 (phosphate groups), 880 cm-1 (CO32- in OH- sites and HPO42-), 1410 cm-1 (CO32- in phosphate sites) and 1550 cm-1 (CO32- in OH- position). All results were related to vibration band at 610 cm-1. A preferential loss of carbonates in the two possible sites was always observed for 10 or 15 minutes, followed by a high release of phosphate. The increase of pH or small amounts of fluoride displaced the preferential carbonate loss to longer times. In the presence of higher fluoride levels a disappearance of the preferential loss of carbonates was noted. A continuous increase of HPO42- in the absence of fluoride occurred; however a straight line with a smaller shape was present, with fluoride addition.

Apatites↗
PubMed1978

Human salivary protein interaction with fluoridated synthetic hydroxyapatite.

Adsorption of human salivary protein on synthetic hydroxyapatite after fluoridation of the mineral phase was tested using an experimental system previously described. The salivary protein adsorption on fluoridated apatite was considerably decreased compared to the adsorption obtained with untreated hydroxyapatite. The calcium-precipitable human salivary glycoprotein still seemed to be selectively adsorbed. Liberation of fluoride under the effect of the salivary proteins was also observed. Fluoridation of enamel may decrease pellicle formation with competitive adsorption effect between salivary proteins and fluoride.

Adsorption↗
PubMed1977

Stages in the dissolution of human enamel crystals in dental caries.

Various stages in monocrystal dissolution occurring during human enamel were studied by high resolution transmission electron microscopy. After the development of a central core lesion, two mechanisms by which the dissolution spread laterally to the (100) faces of the crystal could be demonstrated on the basis of the systematic orientation of the crystallographic axes. In the first case, the destruction was developing parallel to (120) planes and the borders were limited by (100) planes. In the second type, the development of the lateral side lesion was observed parallel to (100) planes. The carious destruction of the enamel monocrystal occurred as a result of the development of several lateral side dissolutions of the two types described, proceeding along the entire central core lesion.

Adolescent↗