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THE CRYSTALLIZATION BEHAVIOUR, MACHINABILITY AND BIOACTIVITY CHARACTERIZATION OF SODIUM-POTASIUM MICA AND FLOURAPATITE CONTAINING GLASS CERAMICS The development of new materials for bone implants and substitutes in man has gained major importance over the past twenty years. In addition to metals, alumina, and organic polymers, glasses and glass-ceramics have come especially to the fore. The special combinations of properties, like biocompatibility and bioactivity, required for medical indications can be adjusted and varied in glasses and glass-ceramics. A machinable glass ceramic is defined as a glass ceramic which can be turned, drilled, milled or threaded like metals while the application of such machines to the working of normal glasses or glass ceramics would cause the fracture of the workpiece. The development of such machinable glass ceramics is based on the controlled precipitation of mica (Mg3AlSi3O10F2) phase at least 2/3 of the composition and bioactivity property is maintained by the precipitation of apatite (Ca5(PO4)3F) phase from the base glass composition. The aim of this study is investigating the crystallization behaviours, mechanical properties and in-vitro bioactivity characterizations of machinable glass ceramics having different ratios of mica and apatite phases. In addition to this, figuring out the proper composition and heat treatment process for the machinable glass ceramic as an artificial bone implant. As a result of experimental studies, it was observed that M70A30 composition containing 70% mica and 30% apatite phases, indicated the best machinability property. After applying in-vitro bioactivity characterization tests to the samples of this composition, the precipitation of hydroxyapatite layer on the surfaces was determined. It was also observed that, the thickness of this layer was reached to the level of 2-3 µm after 4 weeks period. |
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