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  • 2000-2004  (1)
  • 1995-1999  (5)
  • Bone regeneration materials  (2)
  • Confocal laser scanning microscopy  (2)
  • thermodynamic properties  (2)
  • 1
    ISSN: 1436-3771
    Keywords: Key words Dentine ; enamel junction ; Odontoblast processes ; Dentinal tubules ; Confocal laser scanning microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The translucency of teeth allows the non-destructive subsurface visualisation of their microstructure by confocal laser scanning microscopy (CLSM) at a level of about 150 μm below the surface. The dentine–enamel junction (DEJ) is accessible only directly adjacent to the cervix of the tooth. Therefore teeth have to be sectioned for studying marginal areas of the dental hard tissue. The potential of the technique for (pseudo) three-dimensional visualisation allows the study of an array of individual confocal images, the interpretation of which is similar to that of macroscopic tomographs (CT-scan, MRI). Additionally, the extended focus mode yields the overlay of individual confocal images in the form of a two-dimensional projection. This mode of operation proved to be particularly suited for the visualisation of odontoblast processes in their whole extension. The three-dimensional junction between enamel and dentine, the branches of the odontoblast processes and their interactions with the DEJ is demonstrable by CLSM without staining or other procedures of sample preparation. The direct microscopic comparison between samples, either fresh or kept in a humid chamber, and Technovit-embedded sample blocks gives evidence that the risk of artefacts by sample storage or by the embedding procedure is minimal. The tomographs limited to subsurface areas of the tissue also exclude mechanical surface artefacts due to grinding or cutting.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mund-, Kiefer- und Gesichtschirurgie 2 (1998), S. 85-90 
    ISSN: 1434-3940
    Keywords: Schlüsselwörter Strahlenkaries ; In-vitro-Demineralisation ; Konfokale Laser-Scanning-Mikroskopie ; Key words Radiation caries ; In vitro demineralisation ; Confocal laser scanning microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Objective: The volume of literature on radiation-induced caries is still inconsistent as regards the state of the art. Our histotomographic studies have shown direct radiogenic effects on the dentoenamel junction (atrophy of the odontoblast processes). Whether there are direct effects of radiation on dental enamel is not yet known. Material and Method: Sound teeth (group 1, n = 10) were compared either with enamel specimens after high dose in vitro radiation (500– 2500 Gy; group 2; n = 10) and after experimental enoral in situ irradiation (60 Gy; group 3; n = 20), or with teeth from patients after cancer radiotherapy (36 Gy; group 4; n = 20) and with teeth which had obviously decayed due to cancer radiotherapy (60 Gy; group 5; n = 20). Vestibular enamel surfaces of the teeth were exposed to identical in vitro demineralizations (lactic acid gel; pH = 5.0). Each of the samples was prospectively studied histologically by confocal laser scanning microscopy (CLSM) after 90, 180 and 270 min of acid interaction. Data were interpreted micromorphometrically (width of the demineralized area) and micromorphologically. Results: The width of the demineralized area varies between the two in vivo irradiated groups of specimens (group 4: P 〈 0.01; group 5: P 〈 0.001) and the high dose in vitro irradiated teeth (P 〈 0.01) and is significantly different from the sound controls. The histological image of the demineralization in subsurface areas in the teeth of radiotherapy patients is characterized by a total loss of the prismatic structure (homogeneously, amorphous substance). Conclusions: Direct radiogenic effects at the dentoenamel junction have been described earlier. The additional information offered by this study is that there are significant micromorphometric differences in the demineralizing behaviour of irradiated enamel. Obviously, enamel is less resistant to acid attack after irradiation.
    Notes: Fragestellung: Das umfangreiche Schrifttum zur Strahlenkaries zeigt den kontroversen Forschungsstand. Eigene Untersuchungen haben direkt radiogene Veränderungen an der Schmelz-Dentin-Grenze histotomographisch nachweisen können (Atrophie der Odontoblastenfortsätze). Offen ist die Frage nach direkten Strahlenfolgen im Schmelz. Material und Methode: Gesunde Zähne (Gr. 1, n = 10) wurden mit Proben nach hochdosierter In-vitro- (500–2500 Gy, Gr. 2, n = 20) und nach experimentell-enoraler In-situ-Bestrahlung (60 Gy, Gr. 3, n = 20) sowie mit Zähnen von Patienten nach präoperativer Strahlentherapie (36 Gy, Gr. 4, n = 20) und strahlenkariösen Zähnen nach tumortherapeutischer Strahlendosis (60 Gy, Gr. 5, n = 20) verglichen. Im direkten Parallelgruppenvergleich erfolgte eine standardisierte In-vitro-Demineralisierung (Milchsäuregel pH 5,0) an den vestibulären Schmelzoberflächen. Jede Probe wurde prospektiv histologisch durch konfokale Laser-Scanning-Mikroskopie (CLSM) nach 90, 180 und 270 min Entmineralisierung untersucht. Die Auswertung erfolgte mikromorphometrisch (Breite des Demineralisationssaums) und mikromorphologisch. Ergebnisse: Die Breite des Demineralisationssaums unterschied sich sowohl bei beiden in vivo bestrahlten Probengruppen (Gr. 4: p 〈 0,01; Gr. 5: p 〈 0,001) als auch bei den hochdosiert in vitro bestrahlten Zähnen (p 〈 0,01) signifikant von den Befunden der gesunden Kontrollen. Das histologische Bild der Demineralisation an den Zahnoberflächen von Radiotherapiepatienten zeigte dabei einen völligen Verlust der Prismenstruktur (homogen amorphe Substanz). Schlußfolgerungen: Direkte Strahlenfolgen an der Schmelz-Dentin-Grenze wurden in früheren Untersuchungen dargestellt. Zusätzlich konnten jetzt signifikante mikromorphometrische Unterschiede im Demineralisierungsverhalten des bestrahlten Schmelzes gezeigt werden. Offensichtlich ist der Schmelz nach der Bestrahlung für einen Säureangriff weniger resistent.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Mund-, Kiefer- und Gesichtschirurgie 3 (1999), S. 92-97 
    ISSN: 1434-3940
    Keywords: Schlüsselwörter Ca-P-Keramiken ; Knochenersatzmaterialien ; Röntgendiffraktometrie ; Kristallisation ; Key words Calciumphospate ceramics ; Bone regeneration materials ; X-ray diffractometry ; Cristallisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Introduction: The crystalline structure of hydroxyapatite (HA) and tricalciumphosphate (TCP) used as bone regeneration materials affects their physical and probably also their biological properties. Varying velocities of the HA solution process seem to be correlated to different results in powder diffraction analysis (RDX) [1], a validated, routine procedure in mineralogy [2, 6] to analyse crystallized materials. As far we know there are no comparative RDX analyses for the TCP materials in clinical use. Goals: The dimension and quality of the crystallization of several bone regeneration materials are analysed by RDX. Material and methods: The materials analysed were divided in different groups: hydroxyapatite, tricalciumphosphate and bioglass. The materials are characterized by the specific intensity curve measurements. Results: The HA products, with the exception of Algipore, seem to be monophasic. Ceros80 and Endobone were the only ones which seem to be totally crystallized. The TCP products Biobase and Cerasorb are nearly monophasic, whereas Ceros82 seems to contain a mixture of 30% HA and 70% β-TCP. All TCPs show a high crystallization. The bioglasses did – as suspected – not show crystalline structures. Discussion: There are many possible causes for inhomogeneous crystallization of the investigated materials, as they are composites of different foreign ions, extremely small crystals or abnormal (deficient) apatites. How this affects the biological behaviour is not known. Summary: We found differences between the examined materials; how this affects the biological behaviour is unknown. Further investigations are neccesary to correlate the characteristics of the materials to the clinical outcome.
    Notes: Einleitung: Die kristalline Struktur von Knochenersatzmaterialien wie Hydroxylapatitkeramiken (HA) oder Trikalziumphosphatkeramiken (TCP) beeinflußt deren physikalische und sicher auch biologische Eigenschaften. Unterschiedliches Löslichkeitsverhalten von synthetischem und biologischem HA scheinen mit unterschiedlichen Ergebnissen in der Röntgenpulverdiffraktometrie (RDX), einem Routineverfahren der Materialwissenschaften [2, 6] zur Analyse kristalliner Strukturen, korreliert zu sein [1]. Vergleichende RDX-Analysen von TCP liegen in der einschlägigen Literatur nicht vor. Best et al. [4] unterstrichen in jüngster Zeit die Bedeutung der Charakterisierung der Knochenersatzmaterialien zum Verständnis der Resorptionsmechanismen [4]. Fragestellung: Ausmaß und Qualität der Kristallisation verschiedener z. Z. verfügbarer Knochenersatzmaterialien wurden mittels RDX-Analyse bestimmt. Material und Methoden: Die verwendeten Materialien wurden in 3 Gruppen eingeteilt: Hydroxylapatitkeramiken, Trikalziumphosphatkeramiken und Biogläser. Anhand der mittels Pulverdiffraktometer gewonnenen Intensitätsspektren können die Materialien hinsichtlich ihrer Zusammensetzung und Kristallisation charakterisiert werden. Ergebnisse: Die HA-Materialien (bis auf Algipore) scheinen monophasige Produkte zu sein, wobei nur Ceros80 und Endobone eine hohe Kristallisation aufweisen. Auch die TCP-Produkte Biobase und Cerasorb sind nahezu monophasig, während Ceros82 aus einer Mischung von 30% HA und 70% β-TCP zu bestehen scheint. Alle TCP weisen einen hohen Kristallisationsgrad auf. Die Biogläser zeigten erwartungsgemäß keine kristallinen Strukturen. Diskussion: Die möglichen Ursachen der inhomogenen Kristallisation der untersuchten Materialien reichen von der Zusammensetzung aus kleinen Einzelkristalliten über Fremdioneneinschlüsse zu defizitären Apatiten durch Kalziumkarbonatbeimengungen. Deren Bedeutung für das biologische Verhalten ist nicht geklärt. Resümee: Es fanden sich Unterschiede zwischen den untersuchten Materialien, deren Bedeutung für das biologische Verhalten nicht geklärt ist. Weiterführende Untersuchungen sind erforderlich, um diese Eigenschaften mit dem klinischen Verhalten zu korrelieren.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-3940
    Keywords: Schlüsselwörter ; Kalziumphosphatkeramiken ; Spezifische Oberfläche ; Knochenersatzmaterialien ; Poren ; Hydroxylapatit ; Key words ; Calciumphosphate ceramics ; Specific surface area ; Bone regeneration materials ; Pores ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: The surface area and the microporosity of bone regeneration materials influence their chemical and ¶biological properties. Therefore, the size of the specific surface area and the distribution of the pore diameters (pores 〈 1 μm) of bone regeneration materials were analyzed within this study. The analyzed hydroxyapatites were of synthetic, bovine, and phytotroph origin. The tricalcium phosphates and the bioglasses included only synthetic materials. The gas adsorption of each specimen was analyzed using a volumetric N2/Kr system (ASAP 2010, Micromeritics). Additionally, for materials with a specific surface area (〉 2 m2/g) the pore size distribution was evaluated by the BJH-method. Two of the ¶materials evaluated astonishingly large dimensions of the specific surface area (BioOss 79.7 m2/g, Algipore new 14.6 m2/g). A medium ¶surface area was found for Algipore old (4.9 m2/g) and Interpore200 ¶(2.64 m2/g). All other included materials showed only small sizes of the specific surface area (Ceros80 ¶1.8 m2/g, Ceros82 1.31 m2/g, Cerasorb 1.2 m2/g, Biobase 0.7 m2/g, Endobone 0.7 m2/g, Perioglas 0.6 m2/g, Allotropat50 0.23 m2/g, Biogran ¶0.2 m2/g). The materials with large and medium sizes of the specific surface area evaluated the following pore diameters: BioOss 2–50 nm, Algipore new 2–100 nm, Algipore old 5–50 nm, Interpore200 2–100 nm. Pore sizes less than 2 nm were not found in relevant numbers. The materials BioOss, old and new Algipore, and Interpore200 contain a large interconnecting mesopore system (diameter 〈 1 μm). For the materials Biobase, Endobone, Perioglas, Allotropat 50, and Biogran this cannot be assumed. The materials Ceros80, Ceros82, and Cerasorb evaluated a specific surface area between those and might include only a small part of these interconnecting pores. An influence of the interconnecting porosity and the different sizes of the specific surface areas on the biological behavior of the bone regeneration materials can be suggested.
    Notes: Fragestellung: Die Oberfläche sowie die Mikro- und Mesoporosität von Knochenersatzmaterialien beeinflussen deren chemische und biologische Eigenschaften. Daher wurden in dieser Untersuchung die Größe der spezifischen Oberfläche sowie die Verteilung der Porendurchmesser (Poren 〈 1 μm) in Knochenersatzmaterialien bestimmt. Material und Methode: Die untersuchten Hydroxylapatite waren synthetischen, bovinen und phytotrophen Ursprungs. Die Trikalziumphosphate und die Biogläser umfassten nur rein synthetische Materialien. ¶Die Gasadsorptionsuntersuchung je einer Probe erfolgte mit Hilfe eines volumetrischen N 2 -Kr-Systems (ASAP 2010, Micromeritics). Zusätzlich wurde für Materialien mit spezifischen Oberflächen ¶〉 2 m 2 /g die Porengrößenverteilung nach der BJH-Methode ermittelt. Ergebnisse: 1. Spezifische Oberfläche: 2 der Materialien zeigten eine auffallend große spezifische Oberfläche (BioOss 79,7 m 2 /g, Algipore neu 14,6 m 2 /g). Eine mittlere Oberfläche zeigten Algipore alt (4,9 m 2 /g) und Interpore 200 (2,64 m 2 /g). Die übrigen Materialien zeigten nur kleine Oberflächen (Ceros 80 1,8 m 2 /g, Ceros 82 ¶1,31 m 2 /g, Cerasorb 1,2 m 2 /g, Biobase 0,7 m 2 /g, Endobone 0,7 m 2 /g, Perioglas 0,6 m 2 /g, Allotropat 50 0,2 m 2 /g, Biogran 0,2 m 2 /g). 2. Häufigkeitsverteilung des Porendurchmessers: Die Materialien mit großen und mittleren spezifischen Oberflächen zeigten folgende Porendurchmesser: BioOss 2–50 nm, Algipore neu 2–¶100 nm, Algipore alt 5–50 nm, Interpore 200 2–100 nm. Porengrößen 〈 2 nm fanden sich kaum. Schlussfolgerungen: Die Materialien BioOss, Algipore alt und neu und Interpore 200 haben ein großes interkonnektierendes Mesoporensystem (Durchmesser 〈 1 μm). Für die Materialien Biobase, Endobone, Perioglas, Allotropat 50 und Biogran ist dies nicht anzunehmen. Die Materialien Ceros 80, Ceros 82 und Cerasorb zeigen eine dazwischen liegende spezifische Oberflächengröße und weisen einen mäßigen Anteil von solchen interkonnektierenden Poren auf. Ein Einfluss der interkonnektierenden Porosität und der deutlich unterschiedlichen spezifischen Oberflächen auf das Verhalten der Knochenersatzmaterialien in vivo ist nahe liegend.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 17 (1996), S. 391-404 
    ISSN: 1572-9567
    Keywords: coexistence curve ; equation of state ; Lennard Jones fluid ; thermodynamic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new equation of state (EOS) is proposed for the Helmholtz energyF of the Lennard Jones fluid which represents the thermodynamic properties over a wide range of temperatures and densities. The EOS is written in the form of a generalized van der Waals equation.F =F u +F v. WhereF u is a hard body contribution andF A an anttractive dispersion force contribution. The expression forF H is closely related to the hybrid Barker Henderson pertubation theory. The construction ofF A is accomplished with the Setzmann Wagner optimization procedure on the basis of virial coefficients and critically assessed computer simulation data. A comparison with the EOS of Johnson et al. shows improvement in the description of the vapor liquid coexistence properties, thepvT data. and in peculiar, of the calorie properties. A comparison with the EOS of Kolafa and Nezbeda which appeared after the bulk of this work was finished shows still by about 30%.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    International journal of thermophysics 19 (1998), S. 1121-1132 
    ISSN: 1572-9567
    Keywords: caloric properties ; density ; equation of state ; nitrogen ; thermodynamic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new formulation describing the thermodynamic properties of nitrogen has been developed. New data sets which have been used to improve the representation of the p–ρ–T surface of gaseous, liquid and supercritical nitrogen, including the saturated states are now available. New measurements on the speed of sound from spherical resonators have been used to improve the accuracy of caloric properties in gaseous and supercritical nitrogen. State-of-the-art algorithms for the optimization of the mathematical structure of the equation and special functional forms for an improved description of the critical region were used to represent even the most accurate data within their experimental uncertainty. The uncertainty in density of the new reference equation of state ranges from ±0.01% between 270 and 350 K at pressures less than 12MPa, within ±0.02% over all other temperatures less than 550 K and pressures less than 12 MPa, and up to a maximum of ±0.6% at the highest pressures. The equation is valid from the triple point to temperatures of 1000 K and pressures up to 2200 MPa. The new formulation yields a reasonable extrapolation up to the limits of chemical stability of nitrogen as indicated by comparison to experimental shock tube data. Constraints regarding the structure of the equation ensure reasonable extrapolated properties up to temperatures and pressures of 5000 K and 25 GPa. For typical calibration applications, the new reference equation is supplemented by a simple but also highly accurate formulation, valid only for supercritical nitrogen between 270 and 350 K at pressures up to 30 MPa.
    Type of Medium: Electronic Resource
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