| Fluorosilicic mica glass-ceramics are especially useful for the fabrication of all-ceramic dental restorations using computer assisted design/computer assisted manufacture (CAD/CAM) devices because of their good machinability. However, the use of mica glass-ceramics made by the traditional method, melting and casting , as CAD/CAM materials for dentistry is limited by the inability to produce the enough strength and the required range of shades and translucency paramount for sound restorations. This severely inhibits widespread use of micaceous materials as dental restoratives. In the study, the effect of each composition in K2O-MgO-MgF2-SiO2 system on sintering were studied respectively and one mica glass-ceramic was obtained , which is fitted to sintering process. Volume colored mica glass-ceramic blocks were fabricated with zirconia based pigments by sintering process. The results were:1 By orthogonal experimental design , the effects of F- Al2O3 B2O3and P205 of K20-MgO-MgF2-SiO2 system on sintering were studied with shrinkage rate as sintering index by differential thermal analysis(DTA) , X-ray diffract ion (XRD) and scanning electron microscopy (SEM), respectively. And newmica-containing ceramics were gotten that are fitted to sintering process. The three point flexual strength , fracture toughness and transmissivity of the glass-ceramics were 122. 1 + 10. 7Mpa, 1. 56 + 0. 05Mpa. m1/2, 0. 26 + 0. 03 , respectively.2 The glass-ceramic blanks were formed by two forming technologies: gel-casting and cool isostatic pressing(CIP) , and then , sintered at the same heating cycle. The two kinds of blanks were compared for transmissivity and microstructure and one result was drawn: CIP is superior to gel-casting.The sintering processes using different heating cycles were studied with shrinkage rate as sintering index, and the initial result was drawn :the sintering mechanism was typical viscous flow one when the soaking temperature was below 800C , and when the soaking temperature was higher than 800C, the leading densification factor was still viscous flow mechanism while there existed competition between densification and crystallization process. The principles of heating cycle used in glass-ceramics sintering process were:a)fast go through the crystallization temperature and heat to the temperature just below the melting point and keep for a short time in order to exit gases and make glass powders mergeing together. b)and then, lower the temperature to a appropriate point and control the crystallization process .3 Fluorosilicic mica glass-ceramics /3. 0mol%yttria-doped zirconia(Y-TZP) composites were fabricated by sintering process and characterized.The mechnical properties of mica glass-ceramics were significantly improved with the imcorporation of Y-TZP. And the flexural strength and fracture toughness of glass-ceramics with 30wt% ZrO2 which did not affect the crystallization process were 324.3 + 12. 3Mpa and 4.2 + 0.11 MPa. irrespectively.4 Colored glass-ceramic blanks were successfully fabricated with mixing zirconia based pigments by sintering process. And the color difference between inner and outer of blanks was less than 0.2. DTA and mechanical test showed that pigments used did not affect crystallization process and mechanical properties of glass-ceramics.5 It was done to study the influence of content of pigments used on reflectivity , Lab values and absorptivity of blanks which mixed with red, yellow and black pigment, respectively .The results approved that the affect of pigments on coloration in the used content range could be measured and added, which provided the possibility of computer color match (CCM) .6 The K/S curves of blanks with different red, yellow and black pigment content were calculated and drawn from color dates of each one.And then, CCM was tried and the color difference between the matched sample and aim one was 3. 68 while the spectrum reflectance curves of both sample coincided with each other on the whole. |
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