Biomedical subjects

P Steuer

Publications and source records attributed to P Steuer.

10 recordsLinked to original sources

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↗