Biomedical subjects

P Steuer

Publications and source records attributed to P Steuer.

16 recordsLinked to original sources

PubMed2000

High-resolution electron microscopy study of synthetic carbonate and aluminum containing apatites.

Aluminum (Al)-containing calcium-deficient carbonated hydroxyapatites were produced by a precipitation method from aqueous solution with carbonate (0-6.1%) and aluminum (0.1-0.5%) concentrations close to those found in biological materials. Two series of apatites were prepared: one at pH 7.0 and another at pH 9. 0. High-resolution electron microscopy has shown that many of them possess structural defects such as screw dislocations, grain boundaries, and central defects. Samples with high carbonate content and high water and high Al(3+) content had a high amount of structural defects. Accordingly, a sample (7Al1) with a relatively high carbonate content (6.1%) and a sample (7Al6) without carbonate but with a relatively high water (2.0 mol) and Al(3+) content (0. 39%) presented the highest amount of structural defects, 54% and 47%, respectively. A sample (7Al13) with a low level of crystalline water (1 mol) and low carbonate (2.5%) showed a small amount of defects. The presence of water associated with Al(3+) induced a high number of crystals having a central defect with a great similarity to the so-called water layer of octacalcium phosphate (OCP). Observed images of all these crystals have shown good correspondence with the computer-simulated image based on the crystal structure of hydroxyapatite, indicating that the addition of Al(3+) and carbonate does not perturb the apatitic structure.

Aluminum↗

PubMed2000

High-resolution electron-microscopic study of the relationship between human enamel and dentin crystals at the dentinoenamel junction.

The development of dentin and of enamel share a common starting locus: the dentinoenamel junction (DEJ). In this study the relationship between enamel and dentin crystals has been investigated in order to highlight the guiding or modulating role of the previously mineralized dentin layer during enamel formation. Observations were made with a high-resolution electron microscope and, after digitalization, image-analysis software was used to obtain digital diffractograms of individual crystals. In general no direct epitaxial growth of enamel crystals onto dentin crystals could be demonstrated. The absence of direct contact between the two kinds of crystals and the presence of amorphous areas within enamel particles at the junction with dentin crystals were always noted. Only in a few cases was the relationship between enamel and dentin crystals observed, which suggested a preorganization of the enamel matrix influenced by the dentin surface structure. This could be explained either by the existence of a proteinaceous continuum between enamel and dentin or by the orientation of enamel proteins by dentin crystals.

Crystallization↗

PubMed1998

First experimental evidence for human dentine crystal formation involving conversion of octacalcium phosphate to hydroxyapatite.

Biological apatite-crystal formation is a complex process starting with heterogeneous nucleation of inorganic calcium phosphate on an organic extracellular matrix [Cuisinier et al. (1995), J. Cryst. Growth, 156, 443-453]. Further stages of crystal growth are also controlled by the organic matrix and both nucleation and growth processes are under cellular control [Mann (1993), Nature (London), 367, 499-505]. The final mineral in calcified tissue is constituted by poorly crystalline hydroxyapatite (HA) with a low Ca:P ratio, containing foreign ions such as carbonate and fluoride. This study reports the first observation of octacalcium phosphate (OCP) [Brown (1962), Nature (London), 196, 1048-1055] in a biological tissue; OCP was found in the central part and HA at the extremities of the same crystal of calcifying dentine. This observation is of key importance in understanding the first nucleation steps of biological mineralization. The presence of OCP in a forming human dentine crystal and the observation in the same tissue of nanometer-sized particles with a HA structure [Houllé et al. (1997), J. Dent. Res. 76, 895-904] clearly proves that two mechanisms, direct nucleation of non-stoichiometric HA crystals and nucleation of OCP, occur simultaneously in same area of mineralization. OCP is found to be a transient phase during the growth of biological crystals. In small crystals, OCP is completely transformed into HA by a hydrolysis reaction (Brown, 1962) and can only be detected in larger crystals because of its slow kinetics of transformation.

Calcium Phosphates↗

PubMed1997

High resolution electron microscopy: structure and growth mechanisms of human dentin crystals.

Biological crystal formation was postulated to begin by a nucleation process. Such processes have been demonstrated for human amelogenesis and bone mineralization. The aim of this study was to confirm if such mechanisms occur during dentin crystal formation. The structure of human fetal dentin crystals and the earliest stages of mineral growth were followed by High Resolution Electron Microscopy (HREM) associated with digitalized image analysis. Micrographs of the mineralization front were first digitalized, and selected areas were transformed in the reciprocal space by Fast Fourier Transform. The resulting diffractograms were compared with computer-simulated diffractograms and used to determine the orientation of crystals. Dentin crystals, found close to the mineralization front, show a structure closely related to that of hydroxyapatite (HA), as determined by comparison of HREM images with simulated images. These crystals present numerous structural defects such as dislocations and grain boundaries. These defects appear to be present in dentin crystals at an early stage of growth. We have also observed nanometer-sized particles in mineralization areas. Calculated diffractograms of these areas show significant similarities with HA diffraction patterns, and in one case, their structure could be correlated to HA structure through an image simulation process. These nanometer-sized particles could be related to the nucleation process, and their growth, orientation, and formation appear to be mediated by extracellular matrix components.

Crystallization↗

PubMed1993

Human amelogenesis: high resolution electron microscopy of nanometer-sized particles.

Growth of inorganic crystals of enamel is described as a two-stage process with growth of ribbon-like crystals in length and width, followed by their development in thickness. In early stages of crystal growth during human amelogenesis nanometer-sized particles with a mean diameter of 1.1 nm were described between ribbon-like crystals. These small particles had a crystalline structure but their lattice parameters did not seem to be directly related to those of calcium phosphates. The nanometer-sized particles appear to correspond to initial stages of apatite crystal growth. Their localization close to ribbon-like crystals and their progressive increase in size and number may indicate that they represent a precursor phase for these crystals. Nucleation areas at both extremities, of elongated ribbon-like crystals could be involved in the two-directional growth of ribbons and/or in nanometer-sized particle nucleation.

Amelogenesis↗

PubMed1993

Observation of the loss of the hydroxyapatite sixfold symmetry in a human fetal tooth enamel crystal.

A deviation from the hydroxyapatite hexagonal symmetry of a human tooth enamel crystal observed by high-resolution electron microscopy is reported. This symmetry deviation is characterized by: (1) 'preferential' planes that can be indexed as (100) with an intensity that differs from the (300) and the other (100) hexagonal equivalent planes; and (2) streaking of higher order reflections in the optical diffractogram of the image of the crystal. Computer simulations show that similar 'preferential' planes can also be observed at specific crystal tilt angles (and/or beam tilt and/or objective aperture misalignment) and at crystal thickness/microscope defocus values in images of hydroxyapatite crystals observed along the [0001] or [2243] zone axes. The streaking of higher order reflections in the optical diffractogram is related to a deformation of the crystal itself and does indeed show a symmetry deviation of the crystal under observation.

Crystallography↗

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↗

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

Ultrastructural study on human root caries.

Superficial root caries lesions of incisors and premolars of 24 patients aged 52-60 years were studied by scanning electron microscopy and transmission electron microscopy. In the predominantly gram-positive bacteria of the root dental plaque, a great number of corncob configurations were observed. Bacterial infiltration into cementum occurred without any gradient of demineralization and mainly followed the borders between calcified cementum bundles as well as incremental lines. The narrow channels which were filled initially by a single row of gram-positive bacteria broadened progressively with simultaneous destruction of the apatite minerals and the collagenous matrix. Root dentin invasion showed great similarities to coronal dentin with an important gradient of demineralization. In the deep layers, sclerosed tubules contained sometimes rhombohedral crystals. In more superficial layers, bacterial invasion occurred initially in still partially sclerosed tubules. Tubular lumens as well as lateral side branches which had lost their peritubular dentin were filled with gram-positive microorganisms. An important diffuse destruction of the apatite minerals was observed at this stage in the intertubular dentin which still presented typical cross-banded collagen fibrils. The confluence of enlarged dentinal tubules filled by numerous microorganisms led to large bacterial zones with complete destruction of root dentin.

Bacteria↗

PubMed1988

Transmission electron microscopy of the human odontoblast process in peripheral root dentine.

Various methods of fixation were tried on dentine of 45 premolars from children. Two methods based on immediate or delayed use of liquid nitrogen, as well as a cryoprotector (10 per cent dimethylsulphoxid), gave the best results in transmission electron microscopy. Using these methods, the presence of an odontoblast process could be demonstrated in the inner, middle and peripheral human root dentine. The presence of unmyelinated nerve fibril in outer root dentine supports the hypothesis of direct neural stimulation in peripheral dentine.

Adolescent↗

PubMed1986

Ultrastructural development of dated plaque in case of denture stomatitis.

Using special acrylic discs glued into the palatal surface of a denture the development of denture plaque in a case of denture stomatitis as well as the relationships between the denture surface, pellicle, plaque and palatal epithelium were studied with transmission electron microscopy after 30 mn, 1 h, 4 h, 8 h, 24 h, 48 h, 9 days and 29 days. A thin pellicle which increased in thickness from 9 hours to 28 days was visible at the surface of the acrylic denture. It appeared that bacteria retained in the palatal epithelial intercellular spaces were the source of the plaque which developed at the surface of the acrylic denture. Initially loosely packed cocci-like and a few rod-shaped Gram positive bacteria appeared in 8 hours samples at the denture-epithelium interface. An important increase in denture plaque thickness was noted between 24 and 48 hours. In 9 and 28 days samples, coccoid and rod-shaped Gram positive and Gram negative bacteria were present and filamentous bacteria began to be apparent. In all the samples studied, Candida was rare.

Acrylic Resins↗

PubMed1985

Transmission electron microscopy of plaque accumulations in denture stomatitis.

Denture pellicle in denture stomatitis has been studied with transmission electron microscopy after embedding the denture base in a water-miscible resin in seven patients with heavy plaque deposits on their dentures and in five patients with no apparent plaque accumulation. In the first group, the denture surface was covered by a well differentiated granular pellicle. A cell-free zone was interposed between the pellicle and the plaque, which consisted predominantly of rounded, rod-shaped, and filamentous microorganisms with a loose distribution, separated by an electron-lucent amorphous and gel-like matrix. C. albicans were scattered among the bacteria and often presented with degenerated cytoplasm. In the second group, a structurally heterogeneous pellicle was seen adjacent to the denture surface. A thin plaque that consisted mainly of dense accumulations of C. albicans, a narrow dense matrix, and few bacteria was found. Calculus accumulations on the dentures consisted of amicrobial calcifications in the deeper layers, whereas the superficial parts showed bacterial calcifications.

Bacteria↗

PubMed1985

The extent of the human odontoblast process as determined by transmission electron microscopy: the hypothesis of a retractable suspensor system.

After fixation of fully formed human permanent teeth in liquid nitrogen the extent of the odontoblast process has been studied in transmission electron microscopy. The odontoblast process, limited by a trilaminar plasma membrane, was found just under the dentine-enamel junction. In cross section, the cytoplasm contained a granular mass with light and/or dense core granules. Bare unmyelinated nerve-like fibrils were seen in close connection with the odontoblast process. In the periodontoblastic space non calcified collagen fibrils were occasionally present. Cytoplasmic globules and granules limited by a trilaminar membrane, with occasional myelinic figures were also noted in the peripheral tubular lumens. The hypothesis of a retractable suspensor system is advanced to explain why in normal fixation conditions the odontoblast processes associated with nerve fibrils have not been observed in the outer layers of dentine.

Adolescent↗

PubMed1977

[Ultrastructure of the ligamental surface of the rat alveolar process].

The ultrastructural study of the alveolar bone surface of adult rat molars has shown the presence of resting, developing and resorbing areas. Intermediary, tight and gap junctions were observed between the cell processes of osteoblasts and osteocytes. In developing zones, the progressive differentiation of bone lacunae was followed. In resting zones, fibroblast-like cells with large intercellular spaces were observed. The ultrastructure of the osteocytes and the organic periosteocytic space was variable. The osteoclastic resorption showed an initial mineral attack followed by a collagen breakdown. Some observations suggested a relationship between the osteocytes and the origin of the osteoclast.

Alveolar Process↗

PubMed1977

[Ultrastructural study of the cellular cementum in rats].

The study of the cementum of adult rat molars has essentially shown resting and developing surfaces. The resting cementum surface is covered by fibroblasts oriented perpendicular to the surface and surrounded by collagen bundles entering perpendicularly in the cementum or oriented parallel to the surface. On the surfaces with apposition, cementoblats and cementoid cementoblasts, becoming finally cementocytes, were observed. A decrease in cytoplasmic organelles is noted in these latter cells when going from the surface to the cementum depth. An organic pericementocytic space is located between the comentocyte cytoplasmic membrane and the lacunar calcified wall. In the interlacunar tubules, tight and gap junctions were present between the cytoplasmic processes of adjacent cells. Groupings of several epithelial-like cells were embedded in large intracemental cavities. They probably correspond to epithelial rests of Malassez.

Animals↗

PubMed1976

[Ultrastructure of the alveolodental ligament of the rat].

The ultrastructural study of periodontal ligaments of adult rat molars showed that the predominant cellular element consisted of fibroblasts and fibrocytes. These cells were responsible for the elaboration of the collagen precursors and for their destruction as was demonstrated by the presence of ellipsoidal intracytoplasmic vacuoles containing collagen. The abundance of microfilaments and microtubules as well as the presence of intermediary and tight junctions and nexus between the cell processes seemed to indicate that these cells are contractile and motile. Other cell types were intrequent. The ligament presented a high density of collagen fibrils grouped in bundles. Oxytalan fibrils were also observed. The blood capillaries showed mainly a continuous endothelium. Numerous myelinated and non-myelinated nerve fibrils, as well as nerve endings and mechano-receptors were identified.

Animals↗