Clinical applications of glass-ceramics in dentistry

Glass-ceramics featuring special properties can be used as a basis to develop biomaterials. It is generally differentiated between highly durable biomaterials for restorative dental applications and bioactive glass-ceramics for medical use, for example, bone replacements. In detail, this paper presents one biomaterial from each of these two groups of materials. In respect to the restorative dental biomaterials, the authors give an overview of the most important glass-ceramics for clinical applications. Leucite, leucite-apatite, lithium disilicate and apatite containing glass-ceramics represent biomaterials for these applications. In detail, the authors report on nucleation and crystallization mechanisms and properties of leucite-apatite glass-ceramics. The mechanism of apatite nucleation is characterized by a heterogeneous process. Primary crystal phases of α - and β -NaCaPO₄ were determined. Rhenanite glass-ceramics represent biomaterials with high surface reactivity in simulated body fluid, SBF, and exhibit reactive behaviour in tests with bone cells. Cell adhesion phenomena and cell growth were observed. Suitable colonization and proliferation and differentiation of cells as a preliminary stage in the development of a material for bone regeneration applications was established. The authors conclude that the processes of heterogeneous nucleation and crystallization are important for controlling the required reactions in both biomaterial groups.     

Neue Wege zur seismischen Ertüchtigung von Weltkulturerbe im Lehmbau: Das Beispiel der Zitadelle von Bam,Iran

Im Dezember 2003 zerstörte ein schweres Erdbeben die Stadt Bam in Südostiran. Opfer der verheerenden Zerstörung wurde nicht nur die bewohnte Neustadt, sondern auch die historische Zitadellenanlage aus Lehm. Sie ist eines der größten Komplexe, die komplett aus Lehmwerkstoffen errichtet worden sind. Die sofort im Anschluss ergriffenen Restaurierungs‐ und Rekonstruktionsbemühungen sind auf Grund des extremen Ausmaßes der Zerstörungen stark durch den Wunsch geprägt sowohl die geretteten Reste, als auch rekonstruierte Bauteile gegen seismische Einwirkungen zu ertüchtigen. In diesem Zusammenhang sind auch die Arbeiten des Lehrstuhls für Tragwerksplanung der TU Dresden (Inhaber Prof. W. Jäger) in Bam zu betrachten. Um dieser Aufgabenstellung in einer Weltkulturerbestätte gerecht zu werden, mussten neue Technologien entwickelt und in die Praxis umgesetzt werden. Diesen neuen Technologien widmet sich dieser Beitrag. New approaches for seismic retrofitting of world heritage: The Citadel of Bam, Iran. In December 2003 a heavy earthquake destroyed the city of Bam in southeast Iran. The destructions affected not only the new town of Bam but also the historical Citadel constructed entirely with earthen materials. The rehabilitation measures commenced immediately and are characterized by the desire of defining methods that strengthen the preserved rests against future seismic activity. The projects of the Dresden University of Technology, department of structural design (Head: Prof. Dr.‐Ing. W. Jaeger) presented here, are to be seen as a part of these efforts. In order to meet the demands of heritage conservation within a world heritage site (listed in 2004), new methods and technologies had to be developed and applied. The presented article intends to give a figure of these works.     

State-of-the art comparability of corrected emission spectra. 1. Spectral correction with physical transfer standards and spectral fluorescence standards by expert laboratories

The development of fluorescence applications in the life and material sciences has proceeded largely without sufficient concern for the measurement uncertainties related to the characterization of fluorescence instruments. In this first part of a two-part series on the state-of-the-art comparability of corrected emission spectra, four National Metrology Institutes active in high-precision steady-state fluorometry performed a first comparison of fluorescence measurement capabilities by evaluating physical transfer standard (PTS)-based and reference material (RM)-based calibration methods. To identify achievable comparability and sources of error in instrument calibration, the emission spectra of three test dyes in the wavelength region from 300 to 770 nm were corrected and compared using both calibration methods. The results, obtained for typical spectrofluorometric (0°/90° transmitting) and colorimetric (45°/0° front-face) measurement geometries, demonstrated a comparability of corrected emission spectra within a relative standard uncertainty of 4.2% for PTS- and 2.4% for RM-based spectral correction when measurements and calibrations were performed under identical conditions. Moreover, the emission spectra of RMs F001 to F005, certified by BAM, Federal Institute for Materials Research and Testing, were confirmed. These RMs were subsequently used for the assessment of the comparability of RM-based corrected emission spectra of field laboratories using common commercial spectrofluorometers and routine measurement conditions in part 2 of this series (subsequent paper in this issue).     

State-of-the art comparability of corrected emission spectra. 2. Field laboratory assessment of calibration performance using spectral fluorescence standards

In the second part of this two-part series on the state-of-the-art comparability of corrected emission spectra, we have extended this assessment to the broader community of fluorescence spectroscopists by involving 12 field laboratories that were randomly selected on the basis of their fluorescence measuring equipment. These laboratories performed a reference material (RM)-based fluorometer calibration with commercially available spectral fluorescence standards following a standard operating procedure that involved routine measurement conditions and the data evaluation software LINKCORR developed and provided by the Federal Institute for Materials Research and Testing (BAM). This instrument-specific emission correction curve was subsequently used for the determination of the corrected emission spectra of three test dyes, X, QS, and Y, revealing an average accuracy of 6.8% for the corrected emission spectra. This compares well with the relative standard uncertainties of 4.2% for physical standard-based spectral corrections demonstrated in the first part of this study (previous paper in this issue) involving an international group of four expert laboratories. The excellent comparability of the measurements of the field laboratories also demonstrates the effectiveness of RM-based correction procedures.