silicon and diopside

Diopside ceramic pellets with a nominal composition of 55.5 wt % SiO(2)-25.9 wt % CaO-18.0 wt % MgO were soaked in human parotid saliva (HPS) over different time intervals, to investigate the behavior of the material in a natural medium of high protein content. The results showed the formation of a hydroxyapatite (HA)-like layer on the surface of the ceramic, and suggested that the mechanism of HA-like layer formation in saliva was similar to that showed in vitro test by other silica-based materials. The HA-like layer formed at the interface was found to be compact, continuous, and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study concluded that the high pH conditions (9.8) existing right at the ceramic/human parotid saliva interface promoted HA-like phase precipitation. At this stage of the study, it is possible to suggest that the diopside ceramic could be of interest in specific periodontal applications for bone restorative purposes. Morphology, structure, and composition of the interfacial reaction product were examined by Scanning and Transmission Electron Microscopy techniques (SEM and TEM), combined with Energy Dispersive X-say Spectroscopy (EDS). Changes in ionic concentrations were measured using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), while the pH right at the interface of diopside/PHS were determined with an Ion Sensitive Field Effect Transistor (ISFET-Meter) instruments.

Topics: Bone and Bones; Bone Substitutes; Calcium; Calcium Compounds; Ceramics; Dentin; Humans; Hydrogen-Ion Concentration; Ions; Magnesium Oxide; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Oxides; Parotid Gland; Phosphorus; Saliva; Silicic Acid; Silicon; Silicon Dioxide; Spectrometry, X-Ray Emission; Temperature; Time Factors; X-Ray Diffraction; X-Rays

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Topics: Aluminum; Aluminum Compounds; Calcium; Ceramics; Crystallography; Dental Porcelain; Elasticity; Electron Probe Microanalysis; Fluorides; Glass; Hardness; Lithium; Lithium Compounds; Magnesium; Magnesium Silicates; Materials Testing; Potassium; Silicic Acid; Silicon; Stress, Mechanical; Surface Properties; X-Ray Diffraction; Zirconium