PubMed · 3250895
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A Specht. 1988. [Ceramic partial denture with active attachment].. https://pubmed.ncbi.nlm.nih.gov/3250895/
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A NASICON-type ceramic (high sodium ion conductor) is proposed to record bioelectric signals. The electrode does not need gel before its application. The principle of the measurements is based on a sodium ion exchange between the skin and the material. Electrical measurements performed in saline solutions show that the electrode is slightly polarisable. The skin-electrode impedance was investigated. The impedance decreases as a function of the time of application. The resistive component is the major source of the impedance change. This can be explained by the perspiration process which occurs immediately with time after the application of the NASICON-based electrode on the skin. The skin condition is also an important parameter. NaCl saline solution or abrasion causes the resistance to decrease markedly.
Calcium phosphate ceramics are biocompatible and may develop interactions with human living bone tissues. They are used clinically on the surface of orthopaedic implants to improve primary fixation or in the form of porous blocks. Their brittleness is often advanced as a limitation of their common clinical use. In order to study the influence of porosity on the mechanical strength of calcium phosphate ceramics, we have tested 150 cylindrical hydroxyapatite samples with open porosity. The total porous volume of the ceramics has been varied from 20% to 60% and the pore size from 5 microns to 400 microns. The result indicates that not only total porosity but also pore size can influence compressive strength, which is in good agreement with theoretical work. After mathematical treatment of the results, the experiments have been modelled in the form of a polynomial equation which can be used to predict and optimize mechanical strength. Moreover, this work supports the fact that compressive strength of controlled open porosity implants can be comparable with that of cancellous or cortical human bone, and suggests that porosity should be fitted to clinical application.
Hydroxyapatite ceramic tapes (several hundred micrometres thick), have been prepared at different porosity levels, using the tape casting technique. The reactions, which occur during processing and sintering of the tapes, have been characterized by power X-ray diffraction analysis, differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Volume changes have been measured during different stages of heat treatment. These can be attributed to phase transformations of the starting materials, which determine the sintering behaviour and final porosity of the samples. Measurements of the elastic modulus were performed by the resonant frequency method. A cubic dependence on the relative density is found. Finally, some possible improvements for the technique and selection of powders are suggested, based on the reported results.