Sintering Technologic Improvement And Computer Color Matching Of Dental Machinable Fluorosilicic Mica Glass-Ceramic

Fluorosilicic mica glass-ceramic has become an ideal kind of dental all-ceramic material fabricated by CAD/CAM technique because of its proper machinability, strength and translucency. However, the traditional fabricating method for this material, the melting and casting technique, was inhibited in widespread application for dental restorative purpose because of its series of inherent demerits, such as over-high melting temperature, limitation to append additives and pigments, inability to produce enough strength and changeful colors, et al. In the study, the feasible improved sintering technology of K₂O-MgO-MgF₂-SiO₂ glass system was established by investigating the sintering mechanisms of the glass-ceramic system. The sintered fluorosilicic mica glass-ceramic with wonderful compactness along with a series of excellent mechanical performances was prepared by the improved sintering technology. Furthermore, the wholly inner-colorized fluorosilicic mica glass-ceramic blocks were fabricated successfully by appending the zirconate-based pigments and adopting the improved sintering pigmentation technology, and the effects of appended pigments on sintering behaviors and mechanical performances of the colorized glass-ceramics were investigated at the same time. On the base of the spectral datum of monochromatic glass-ceramic samples, the modern computercolor matching techniques were applied in matching colors of the mica glass-ceramic samples with series of target colorized samples (partial VITAMARK II colorized ceramic blocks and partial VITAPAN 3D-MASTER shade tabs), and the matching expectations were realized. The results of the study are as follow:1. The effects of temperature on the sintering behaviors of fluorosilicic mica glass powder of two different particle sizes were investigated. The results as follow were obtained: the sintering process of this glass system belongs to viscous flow mechanism; the shrinkage would be increased going with the rise of temperature; the shrinkage of the smaller-size powder was evidently higher than that of the bigger one; both sizes of the glass powder revealed low viscosity and good sintering performances at their medium temperature sections. The results above suggested that choosing the smaller size of glass, intensifying sintering process at its medium temperature section and then rapidly heating up to the ultimate temperature could possibly improve the compactness of the glass-ceramic.2. The effects of the heat-preserving-time on sintering behaviors of fluorosilicic mica glass powder of two different particle sizes were investigated and the following results were obtained: the shrinkages of both sizes of glass powder were increased and the increasing velocities were more and more slower going with prolongation of the heat-preserving-time; the shrinkage of the small-size powder was evidently higher than the bigger one; the smaller-size powder needed much shorter heat-preserving-time to achieve ultimate compactness than the bigger one.3. The effects of the calefactive velocity on sintering behaviors of fluorosilicic mica glass powder of two different particle sizes were investigated and the following results were obtained: for both sizes of the glass powder, the faster the calefactive velocity was, the higher the shrinkage would be; the shrinkage of the small-size powder was still evidently higher than the bigger one.4. The effects of the ultimate sintering temperatures on crystalline structures andmechanical performances of fluorosilicic mica glass-ceramics were investigated. The results indicated that the primary crystals of all the glass-ceramics sintered at different ultimate temperatures within 1100-1200 °C were tetrasilicate fluoriod mica crystals, but that the crystalline phase decreased while glass phase increased in the glass-ceramics as the temperatures were higher than 1120°C, which led to poorer mechanical performances of glass-ceramics. Therefore, the proper ultimate temperature should be 1120 °C.5. Sintered by the improved technology, the fluorosilicic mica glass-ceramic with more excellent compactness and mechanical performances was prepared successfully. The flexural strength, fracture toughness and ray penetrating ratio of the glass-ceramic were 136.4±7.1Mpa, 1.66±0.04Mpa.m1/2 and 0.29±0.05 respectively.6. Colorized fluorosilicic mica glass-ceramics were fabricated successfully by appending zirconate-based pigments to small-size glass powder and sintering them with the improved sintering technology. The results of DTA, XRD, mechanical testing and scanning electron microscope drew the coincidental conclusion that appending pigments had no remarkable effects on the crystalloid behaviors and mechanical performances of the glass-ceramics.7. The monochromatic fluorosilicic mica glass-ceramic samples with different concentrations of pigments were prepared and their chroma values and reflective spectrums were mensurated and investigated. The datum above indicated that the relationship between the concentrations of pigments and the chroma values accorded with the principles of pigmentation, and that the spectral reflectivity groups of monochromatic samples were feasible for establishing database of computer-color-matching software.8. Two kinds of computer color matching techniques were applied for matching the colorized fluorosilicic mica glass-ceramics with series of VITAMARK II colorized ceramic blocks and VITAPAN 3D-MASTER shade tabs. The results...