The Basic Research Of A Dental Machinable Ceramic Based On Diatomite

Because of its good biocompatibility and aesthetics, dental all-ceramic restorations have extensive applications in clinical practice. In many of the ceramic materials, machinable ceramics combined the computer aided design / manufacture technology (CAD/CAM) can quickly and accurately produce restorations. The ceramic blocks produced by the factory can more easily to control the mechanical and aesthetic properties of the material. The groundbreaking of CAD/CAM technology made oral fixed prosthesis design and production technology revolutionized changes. The machinable ceramics provided CAD/CAM technology with not only material foundation but also the diversification of development goals. Therefore, it has important practical value to develop dental machinable ceramics with low melting point, high strength and high toughness, especially simple processing in oral clinical prosthesis.The first part of this project selected dental pressable ceramics Cergo on market as the research object and analyzed its chemical composition and microstructure before and after sintering. The mechanical properties (Microhardness and density) of Cergo before and after sintering were also recorded. Through the analysis of the changes in sintering process on the material, the relationship between the properties and structure of materials was proved. It took examples for preparing the new type of diatomite-based dental machinable ceramic.In the second part of this project, diatomite was selected as raw material for the first time in China. A new type of diatomite-based dental machinable ceramic was prepared by using the frame structure of diatomite and adding nano flexibilizers to increase mechanical properties of the material. The sintering process was also explored. The mechanical properties and aesthetic performance of the new dental machinable ceramics complied with the requirements of the dental all-ceramics. It has the broad prospect for its favourable properties. Part one Analysis of Composition and microstructure of Cergo hot-pressed dental ceramics before and after sinteringObjective: To explore the composition and microstructure of Cergo hot-pressed dental ceramics before and after sintering. The effects of the sintering process on the material were also explored.Methods: Whole-spectrum direct-reading inductively coupled plasma (ICP) optical emission spectrograph and ultraviolet visible spectrophotometer were used to characterize Cergo hot-pressed dental ceramics before sintering. Thermogravimetric /differential thermal analyzer (TG/DTA) was used to characterize the transformation mechanisms in the process of sintering. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to characterize the crystal form and morphology before and after sintering. The mechanical properties (Microhardness and density) of Cergo before and after sintering were also recorded. The data were analyzed with equal variance followed by two-sample t tests (P<0.05). The three-point bending strength of Cergo after sintering was also recorded.Results: Cergo hot-pressed dental ceramics before sintering is a kind of amorphous ceramic material. It contained silica, alumina, oxidation sodium, caustic potash and some nanoparticles. According to the analysis of XRD and SEM, it generated tetragonal leucite crystals of the glass matrix. The diameter of tetragonal leucite crystals was about 1~3 um in measured. Mean Vickers hardness and density of Cergo were 4.96±0.27GPa and 2.22±0.05g/cm3 respectively, significantly higher than 2.00±0.20 GPaå'Œ1.68±0.07 g/cm3 before heat-pressing (P<0.05). The three-point bending strength of Cergo after sintering was 76.27±9.40MPa.Conclusion: Cergo hot-pressed dental ceramics before sintering is a glass-ceramics in the SiO2—Al2O3—Na2O—K2O system, after high temperature sintering and solid state reaction, it generated compact tetragonal leucite crystals reinforced glass-ceramics. Part Two Properties of Diatomite-based Dental Machinable CeramicObjective Through developing the new type of dental machinable ceramic based on diatomite, the relationship between the structure and properties of the material was studied. It provided basis for the development of the new type of dental ceramics on research.Methods Based on the composition of diatomite, the new dental machinable ceramic was added with nanometer materials and obtained through the treatment of ball-milling, dry-pressing and sintering. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to characterize the crystal form and microstructure. The mechanical properties (three-point bending strength, fracture strength and microhardness) of diatomite-based ceramic were recorded. Four types of the materials were sintered at the temperature for 600, 700, 800, 900 degrees respectively and the machinability were evaluated.Results The material after sintering had smooth surface, oyster white and no crack ivory in it. The internal structure of the material observed in SEM presented polycrystalline structure and the grain boundary clarity. The three-point bending strength, microhardness and fracture toughness of the new dental machinable ceramic reached to 177.23±7.02MPa, 9.73±0.64GPa and 3.93±0.58MP a·m0.5 respectively. The machinability of the material sintered at 700 degrees was good.Conclusion The mechanical and esthetic properties of the new type of diatomite-based dental machinable ceramic were basically qualified but the strength still needs to be increased.