Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Plastic Embedding”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,585 records · Page 88Linked to original sources
PubMed2002

PIXE micro-beam mapping of metals in human peri-implant tissues.

Previous investigations did not agree about the possible presence of titanium and other metals in the tissues around endosteal dental implants and joint prostheses. Indeed, while some authors reported diffusion of metals into the tissues, some others did not find evidence of this phenomenon. In the present study, four dental titanium implants, removed with the surrounding tissues from patients at various time intervals after the insertion, were studied by means of the micro-beam proton-induced X-ray emission (PIXE micro-beam) technique, which draws maps showing the tissue distribution of elements with a detection limit of about 1 ppm. One implant was built in commercially pure titanium, two others in titanium coated with titanium plasma spray, and the fourth in Ti-Al-V alloy. Their composition was confirmed by the PIXE micro-beam analyses. The removed samples were embedded in epoxy and processed with a cutting-grinding appliance, mounted on plastic holders, and ground up to a thickness of about 35 microm. Optical microscope examinations were also carried out, to compare the optical findings with the elemental maps obtained with the PIXE micro-beam. One implant, removed after 70 days because the patient had developed peri-implantitis, had some inflammatory soft tissue attached, with no evidence of metal leakage. The other three implants had been removed after 6, 7 and 9 years of valid clinical service, because of the fracture of the prosthetic abutment or the implant stem. At the optical microscope, all these fixtures were embedded in mature bone. The elemental maps indicated small titanium deposits in about 5% of the bone bordering the implants, while aluminum, when present in the fixture, leaked diffusely into the surrounding bone and vanadium was not found in the tissues. These results suggest that titanium may be found occasionally in peri-implantar tissues, but has very little tendency to spread, while the presence of aluminum in the implant alloy may cause an important leakage of this metal.

Journal Article↗
PubMed2004

Activity-regulated cytoskeletal-associated protein is localized to recently activated excitatory synapses.

Activity-regulated, cytoskeletal-associated protein (Arc) is an immediate early gene induced in excitatory circuits following behavioral episodes. Arc mRNA is targeted to activated regions of the dendrite after long-term potentiation (LTP) of the dentate gyrus, a process dependent on NMDA receptor activation. We used post-embedding immunogold electron microscopy (EM) to test whether synaptic Arc expression patterns are selectively modified by plasticity. Consistent with previous light microscopic observations, Arc protein was rapidly induced in the dentate gyrus following LTP-producing stimulation of the perforant path and was detectable in granule cell nuclei, somata and dendrites after two hours of high frequency stimulation. Post-embedding EM revealed Arc immunogold labeling in three times as many spines in the middle molecular layer of the stimulated dentate gyrus than in either the ipsilateral outer molecular layer or the contralateral middle and outer molecular layers. This upregulation did not occur with low frequency stimulation of the perforant path. Therefore Arc protein localization may be a powerful tool to isolate recently activated dendritic spines.

Animals↗
PubMed1986

Ultrastructural features of the lymphocyte-stimulated halos produced by human glioma-derived cells in vitro.

Many glioma-derived cell lines have the capability of escaping cell-mediated immune attack. One mechanism of escape is the secretion of a hyaluronidase-sensitive mucopolysaccharide coat by these cells. This coat prevents contact and tumor cell killing by specific cytolytic allogeneic lymphocytes. The production of the coat by the tumor cells is stimulated by a macromolecular factor released by peripheral blood mononuclear (PBMC) cells in culture. We have examined the morphologic and ultrastructural features of this extracellular matrix. Three coat-producing lines were studied. Under phase contrast light microscopy, the coat is a clear pericellular 'halo'. To stain this zone, ruthenium red and Alcian Blue 8 G stains, which bind to acid mucopolysaccharides (to a large extent, hyaluronic acid), were used. The two stains produced similar results. With light microscopy, a weblike pattern of stain was evident throughout the halo region. With transmission electron microscopy, staining was found along the plasma membrane of the glioma cells and their microvilli, stretching in long, branching filaments from these surfaces and, in some instances, from one microvillus to the next. Since mucopolysaccharide matrices have a large aqueous component, it was necessary to determine whether dehydration alters the stain pattern. Therefore, undehydrated ruthenium red stained specimens from each culture were embedded in Quetal 651 (Ted Pella, Inc., Tustin, CA), a water soluble plastic. No morphologic differences were noted between the hydrated and dehydrated specimens. This study indicates that numerous long microvilli and a secreted mucopolysaccharide matrix are important structural elements of the lymphocyte-stimulated tumor cell halo in vitro. The mechanism by which the PBMC factor stimulates coat formation and the importance of the coat in in vivo tumor defenses remain to be elucidated.

Brain Neoplasms↗
PubMedDate not supplied

Synapses in hippocampus occupy only 1-2% of cell membranes and are spaced less than half-micron apart: a quantitative ultrastructural analysis with discussion of physiological implications.

Relatively little information exists regarding the spatial structure of synaptic neuropil in the brain. The present electron microscopic study employs unbiased stereological techniques and Monte Carlo simulations to characterise quantitatively the spatial organisation of synaptic circuitry in the dentate gyrus of the hippocampus, an area of particular importance in mechanisms of learning and the subject of a number of experimental neurobiological models of synaptic plasticity such as long-term potentiation. Firstly, tissue shrinkage/expansion resulting from embedding was assessed by imaging 300-microm thick hippocampal slices in the course of the entire embedding protocol, giving a value of 94.3 +/- 1.1% for distance measures and 84.3 +/- 2.8% for volumetric measures. Secondly, numeric synaptic density, Nv, was estimated using the disector. Thirdly, accumulated area of post-synaptic densities (PSDs) per tissue volume, Sv, and the overall cell membrane area per tissue volume, Sv*, were assessed using unbiased stereological rules coupled with image analysis of single sections. Finally, the mean area of individual PSDs was derived as a ratio Sv/Nv giving: 0.0394 microm2 for axo-spinous PSDs (thus representing approximately 1.3% of total cell membranes) and 0.0769 microm2 for dendritic shaft PSDs (approximately 0.25% of total cell membranes). From these data, the mean nearest neighbour distance between synapses was estimated using Monte Carlo simulations of a random 3D arrangement of synapses constrained by PSD sizes (a truncated Poisson process), giving a value of 0.48-0.51 microm. The physiological importance of the morphometric data obtained is discussed in terms of assessing (i) the role of synaptic environment in modifying synaptic efficacy and (ii) the plausibility of cross talk between synapses in relation to extrasynaptic neurotransmitter diffusion and transient depletion of extracellular Ca2+.

Animals↗
PubMed1999

A reduction in the AAPM TG-36 reported peripheral dose distributions with tertiary multileaf collimation. American Association of Physicists in Medicine Task Group 36.

PURPOSE: The American Association of Physicists in Medicine Task Group 36 (AAPM TG-36) data can be used to estimate peripheral dose (PD) distributions outside the primary radiation field. However, the report data apply to linear accelerators not equipped with tertiary multileaf collimators (MLCs). Peripheral dose distributions consist of internal scatter, collimation scatter, transmission through collimation, head leakage, and room scatter. Tertiary MLCs may significantly reduce the PD due to a reduction in collimation scatter, transmission through collimation, and head leakage. Measurements were performed on a multimodality linear accelerator, equipped with a tertiary MLC, to determine PD distributions as a function of energy, field size, distance from the primary radiation field edge, MLC position, and collimator orientation. METHODS AND MATERIALS: Measurements were made using an ionization chamber embedded in a 20 x 40 x 120-cm3 water-equivalent plastic phantom with the secondary collimator and MLC settings of 10 x 10, 15 x 15, 20 x 20, 25 x 25 cm2, and with the MLC fully retracted. Data were taken along the longitudinal axis of the machine for 6 and 18 MV photons. Peripheral dose distributions were evaluated with the collimator set to 180 and 90 degrees. Rotation of the collimator allowed measurements parallel and orthogonal to the direction of motion of the MLC. RESULTS: For both photon energies, peripheral doses measured on a MLC machine were lower than the TG-36 data. When the collimator is rotated by 90 degrees, placing the lower jaws and the MLC leaves along the plane of interest, PD was reduced by as much as a factor of three compared with PDs measured with the MLC fully retracted and the collimator rotated to 180 degrees. PDs measured with the MLC fully retracted and collimator rotated to 180 degrees were comparable to the TG-36 data. Measured PDs were lower when the MLC was used to shape the field than when the MLC was fully retracted. CONCLUSION: A strategic orientation of the collimator with a tertiary MLC can reduce PD distributions by more than a factor of two. This decrease significantly lessens or eliminates the need for external lead shielding to reduce the critical organ dose. This method can be used even when Lipowitz metal blocking (such as for mantle fields) is used, with the MLC leaves oriented along the longitudinal plane.

Particle Accelerators↗
PubMed1984

Radioimmunocytochemistry using a tritiated goat anti-rabbit second antibody.

Affinity-purified goat anti-rabbit immunoglobulin G (GAR) was conjugated with (3H)-propionyl succinimidate and used to localize substance P (SP), enkephalin (ENK), and serotonin immunoreactive sites in the spinal dorsal horn and medulla of the rat and cat. Autoradiographic localization was demonstrated on paraffin, frozen, Vibratome, and 2 micron plastic sections. The latter were obtained from radiolabeled Vibratome sections that were embedded in epoxy resin. The distribution of SP, ENK, and serotonin demonstrated by radioimmunocytochemistry was comparable to that observed on semiadjacent sections using peroxidase-antiperoxidase (PAP) immunocytochemistry. The autoradiograms, however, were generated using primary antibody concentrations up to five times more dilute than concentrations used for the PAP procedure. Indirect radioimmunocytochemistry using a (3H) anti-immunoglobulin G second antibody can be used to localize a variety of monoclonal and polyclonal antisera. It is quantifiable at the light microscopic level and can be potentially used with peroxidase histochemistry to double label immunoreactive structures at the ultrastructural level.

Animals↗
PubMed2004

THz transmission spectroscopy and imaging: application to the energetic materials PBX 9501 and PBX 9502.

We report the measurement of the effective complex index of refraction near 1 THz for the Plastic-Bonded eXplosives PBX 9501 and PBX 9502. These plastic-bonded explosives consist of organic crystalline energetic materials, HMX and TATB, embedded in a binder matrix. We find that they are partially transparent at a few hundred GHz and we have applied a two-dimensional imaging technique for the detection of pre-fabricated defects in small samples.

Journal Article↗
PubMed1985

High-resolution microscopy of the implant-tissue interface.

A method is described which permits study of the interface of tissue and bulk implant at the light and electron microscopic level. It is based on epoxy embedding of implant and surrounding tissue with subsequent separation of implant and plastic. The separation takes place at the interface between tissue and implant; neither cells nor matrix are disturbed.

Animals↗
PubMed1996

Bond strengths of fluoride-releasing restorative materials.

PURPOSE: To compare the shear bond strengths to dentin of four tooth-colored fluoride-releasing restorative materials that utilize different mechanisms of dentin-bonding. MATERIALS AND METHODS: Four materials were tested: a chemically-cured glass ionomer (Ketac-Fil); a light-cured resin-modified glass ionomer (Photac-Fil); a light-cured resin-modified glass ionomer in conjunction with a resin dentin-bonding agent (Vitremer); and a light-cured resin composite in conjunction with a resin dentin-bonding agent (Tetric). The enamel was removed from four sides of the twenty human noncarious extracted molars which had their roots embedded in acrylic blocks. Cylindrical samples of the materials were prepared in plastic molds and bonded to the dentin surface according to the manufacturers' instructions. After 24 hours of storage in a humidor, the samples were sheared with an Instron testing machine at a crosshead speed of 0.5 mm/minute. RESULTS: Statistical evaluation (ANOVA and Duncan's test) suggests that the fluoride-releasing resin composite material utilizing a resin dentin-bonding agent provided a significantly greater mean shear bond strength (16.5 MPa) after 24 hours storage than any of the selected glass ionomer materials. Of the three glass ionomer materials compared, the light-cured resin-modified material with a resin dentin-bonding agent provided a significantly greater mean shear bond strength (6.7 MPa) than the light-cured resin-modified material without a resin dentin-bonding agent (3.0 MPa) or the chemically-cured material (3.8 MPa).

Analysis of Variance↗
PubMed1975

Plastic sectioning for light microscopy of Pyrenomycetes.

In preparation for light microscopy, ascocarps of Sordaria fimicola Ces. & DeNot. were embedded in Spurr's medium and sectioned at 1-1.5 mum on an ultramicrotome. Sections were floated on Giemsa staining solution at 60 C for 10-30 min, washed in distilled water, affixed to slides by drying, and mounted in immersion oil. Best preservation of the delicate sterile tissues of the centrum was obtained by fixation in 1% KMnO4 for 2.5-3 hr, followed by the Giemsa stain. This method is suggested for future studies on the morphology of perithecial ascomycetes.

Ascomycota↗
PubMed2003

Staining methods applied to glycol methacrylate embedded tissue sections.

The use of glycol methacrylate (GMA) avoids some technical artifacts, which are usually observed in paraffin-embedded sections, providing good morphological resolution. On the other hand, weak staining have been mentioned during the use of different methods in plastic sections. In the present study, changes in the histological staining procedures have been assayed during the use of staining and histochemical methods in different GMA-embedded tissues. Samples of tongue, submandibular and sublingual glands, cartilage, portions of respiratory tract and nervous ganglion were fixed in 4% formaldehyde and embedded in glycol methacrylate. The sections of tongue and nervous ganglion were stained by H&E. Picrosirius, Toluidine Blue and Sudan Black B methods were applied, respectively, for identification of collagen fibers in submandibular gland, sulfated glycosaminoglycans in cartilage (metachromasia) and myelin lipids in nervous ganglion. Periodic Acid-Schiff (PAS) method was used for detection of glycoconjugates in submandibular gland and cartilage while AB/PAS combined methods were applied for detection of mucins in the respiratory tract. In addition, a combination of Alcian Blue (AB) and Picrosirius methods was also assayed in the sublingual gland sections. The GMA-embedded tissue sections showed an optimal morphological integrity and were favorable to the staining methods employed in the present study. In the sections of tongue and nervous ganglion, a good contrast of basophilic and acidophilic structures was obtained by H&E. An intense eosinophilia was observed either in the striated muscle fibers or in the myelin sheaths in which the lipids were preserved and revealed by Sudan Black B. In the cartilage matrix, a strong metachromasia was revealed by Toluidine Blue in the negatively-charged glycosaminoglycans. In the chondrocytes, glycogen granules were intensely positive to PAS method. Extracellular glycoproteins were also PAS positive in the basal membrane and in the region occupied by the lamina externa and reticular fibers surrounding each smooth muscle cells of the blood vessels. In the epithelial cells of the respiratory tract, acid and neutral mucins were histochemically detected by AB and PAS methods, respectively. Moreover, granules containing acid and neutral mucins were revealed in purple by AB and PAS concomitantly. In the sublingual gland sections, a distinct affinity of acid mucins by AB (in turquoise-blue) and collagen fibers by Picrosirius (in red) was obtained when these methods were combined. Although some routine dyes used in paraffin sections have showed a weak stain in historesin sections, our results showed that different dyes could be applied in GMA sections if modified staining procedures were assayed. Therefore, appropriate staining contrast and, thus, detection of one or different substances in a same section can be acquired in association to the good morphological resolution provided by GMA.

Alcian Blue↗
PubMed2005

Assessment of morphological and immunohistological alterations in long-term keloid skin explants.

One of the major impediments in keloid research is the lack of a keloid animal model that can mimic human keloid. This imposes investigative constraints on studying cellular interactions and biochemical processes that normally occur in vivo. Our main objective is to establish an in vitro model for maintaining long-term viable keloid dermal explants as a tool for investigating the pathogenesis of keloid scar formation. Explants of adult keloid scars were cultured in vitro by embedding them in enriched collagen gel matrix and maintaining them for up to 6 weeks, whereupon changes in tissue morphology and cellular differentiation were examined. The effects of medium enrichment, air versus liquid submersion, and different substrates on the explants were examined. Our results indicated that keloid explants embedded in a collagen gel matrix were morphologically better preserved than explants placed on a plastic substrate. Explants with epidermis at the air-liquid interface had better morphology than collagen-submerged explants, and there were no differences between serum-free and serum-supplemented explant cultures. Immunohistochemical and apoptotic analyses were performed to assess cellular viability and differentiation. In situ hybridization confirmed that keloid fibroblasts had sustained collagen type I gene expression throughout the 6 weeks in culture, thus validating the integrity of a long-term keloid culture system. In conclusion, the collagen-embedded skin explant system demonstrates that keloid tissues could be maintained for up to 6 weeks for long-term in vitro studies.

Cell Differentiation↗
PubMed2000

Synaptic plasticity and memory: an evaluation of the hypothesis.

Changing the strength of connections between neurons is widely assumed to be the mechanism by which memory traces are encoded and stored in the central nervous system. In its most general form, the synaptic plasticity and memory hypothesis states that "activity-dependent synaptic plasticity is induced at appropriate synapses during memory formation and is both necessary and sufficient for the information storage underlying the type of memory mediated by the brain area in which that plasticity is observed." We outline a set of criteria by which this hypothesis can be judged and describe a range of experimental strategies used to investigate it. We review both classical and newly discovered properties of synaptic plasticity and stress the importance of the neural architecture and synaptic learning rules of the network in which it is embedded. The greater part of the article focuses on types of memory mediated by the hippocampus, amygdala, and cortex. We conclude that a wealth of data supports the notion that synaptic plasticity is necessary for learning and memory, but that little data currently supports the notion of sufficiency.

Amygdala↗
PubMed1988

Large area sectioning for morphologic studies of nonhuman primate nasal cavities.

The nasal region is important for studies in inhalation toxicology but is difficult to prepare for histological examination, especially in species as large as primates. A method for the histologic preparation of undecalcified, complete transverse sections of the nonhuman primate nasal cavity is summarized as follows. After removal of excess soft tissue, mandible and calvaria, the head is fixed in 10% neutral buffered formalin. The nasal region is transversely sectioned into serial 3-mm-thick blocks from the nares to the posterior aspect of the soft palate using a low speed saw with a water-cooled diamond-coated blade. The blocks are embedded in a mixture of glycol and methyl methacrylates, with polyethylene glycol-1500 and dibutylphthalate as plasticizers. The plastic blocks average 5.0 x 5.0 x 1.5 cm; 2-4 microns sections are cut on an automated sliding microtome. In spite of the size of the blocks, this technique yields complete transverse sections of the nasal cavities with excellent morphologic detail. The sections are amenable to a wide range of staining procedures. The procedure lends itself to autoradiographic studies. The embedding mixture is ideally suited for studies of undecalcified bone and teeth.

Animals↗
PubMed1990

A rapid embedding procedure for the study of platelet interactions with extracellular matrices in a flowing system. Effect of aspirin on platelet activity.

The cultured endothelial cell (EC) is currently used as a model for the study of the interaction of platelets with the vascular wall. Described is a method for rapid quantitative and qualitative evaluation of platelet interactions with extracellular matrices (ECM) produced by human cultured ECs growing on plastic coverslips. Morphometric calculations can be performed on the same perfused coverslips. A very good correlation (r = 0.96) was found between results of a morphometric method en face and those obtained from analysis of cross sections of the perfused coverslips. A shear rate-dependent increase on platelet deposition onto ECMs was observed with both morphometric procedures. The method is sensitive enough to detect drug-related changes of platelet function. An impairment of the interaction of platelets with the ECM was observed when blood obtained from healthy volunteers who took 500 mg aspirin/day for five days was perfused. Aspirin showed a marked effect, decreasing platelet spreading onto the subendothelium (p less than 0.05). The embedding method described benefits from the use of plastic coverslips that are easily detected from the glycol methacrylate compound used for the embedding procedure. Quantitative analysis en face (covered surface) and qualitative evaluation of platelet interactions (contact, adhesive and aggregated platelets) in cross sections are performed on the same coverslip. This embedding procedure provides a useful tool for the study not only of platelet interactions with ECMs but also for the investigation of interactions of blood elements with other cultured cells.

Aspirin↗
PubMed2002

Cranioplasty with individual carbon fibre reinforced polymere (CFRP) medical grade implants based on CAD/CAM technique.

BACKGROUND: The authors present a new method for the reconstruction of large or complex-formed cranial bone defects using prefabricated, computer-generated, individual CFRP (carbon fibre reinforced plastics) medical grade implants. METHOD: CFRP is a composite material containing carbon fibres embedded in an epoxy resin matrix. It is radiolucent, heat-resistant, extremely strong and light (its weight is 20% that of steel), has a modulus of elasticity close to that of bone, and an established biocompatibility. The utilisation of a CAD/CAM (computer aided design/computer aided manufacture) technique based on digitised computed tomography (CT) data, with stereolithographic modelling as intermediate step, enabled the production of individual, prefabricated CFRP medical grade implants with an arithmetical maximum aberration in extension of less than +/-0.25 mm. Between 1995 and February 2002, 29 patients (15 men and 14 women; mean age, 39.9 years; range, 16 to 67 years) underwent cranioplasty with CFRP medical grade implants at the neurosurgical department of the University of Vienna. Twenty-four patients were repaired secondarily (delayed cranioplasty) while 5 were repaired immediately following craniectomy (single stage cranioplasty). All cases were assessed for the accuracy of the intra-operative fit of the implant, restoration of the natural skull contour and aesthetics and adverse symptoms. FINDINGS: The intra-operative fit was excellent in 93.1% and good in 6.9% of the implants. In two cases minor adjustments of the bony margin of the defect were required. The operating time for insertion ranged from 16 to 38 minutes, median 21 minutes. Postoperatively, 86.2% of the patients graded the restoration of their natural skull shape and symmetry as excellent while 13.8% termed it good. In one patient a non-space occupying subdural hygroma was found at the follow-up, but required no intervention. Two patients experienced atrophy of the frontal portion of the temporal muscle while one patient had a transient palsy of the frontal branch of the facial nerve. Over the mean follow-up period of 3.3 years (range, 0.08 to 6.8 years), there were no adverse reactions and no plate had to be removed. INTERPRETATION: Individual, prefabricated CFRP medical grade implants may be considered as an alternative to conventionally utilised materials for cranioplasty, in particular in the challenging group of patients with extensive cranial defects or more complex-formed defects of the fronto-orbital or temporo-zygomatic region, guaranteeing short operating times and excellent functional and aesthetic results, which justifies the expense of their production.

Adolescent↗
PubMed2004

Simulating periodontal effects in dental osseointegrated implants: effect of an intramobile damping element on the fatigue strength of dental implants--an in vitro test method.

OBJECTIVE: The purpose of this study was to develop and adapt a new method for testing dental implant systems and to apply it to existing systems with and without dampers. The parameters examined were the fatigue strength of the superstructure-retaining titanium screw, the deformation of the damper, and the effect on the supporting, bone-stimulating, and embedding material. METHOD AND MATERIALS: Ten pairs of implant specimens were prepared according to standard laboratory procedure and embedded in transparent polymethylmethacrylate (PMMA). Five pairs were provided with polyoxymethylene dampers and five with nondamping titanium connectors. Each pair was connected with a metal beam, and cyclic loads were applied with a pneumatic-driven machine at a frequency of 2 Hz. Chewing forces of 150 to 450 N were transmitted by springs individual to each specimen. For each of the 2 x 10(5) cycles, there was a control of the retaining screw and bonding between the fixture and embedding material by registration of gap propagation in the implant-PMMA interface. RESULTS: A significant damping effect was noticed on the implant--embedding material interface. Damping did affect the superstructure, since the retaining screws were plastically deformed. The screws were unscrewed when the applied load exceeded 300 N, while the undamped system was seemingly unaffected. CONCLUSION: The study method made it possible to evaluate damping effects on different levels of implant systems, while satisfying the requirements for testing in a "clinical-like" way. PMMA was comparable to bone in supporting implants during fatigue testing.

Alveolar Process↗