| Dentistry can't be away from metal, such as inlay, crown and bridge, frame of artificial teeth, implant and so on. In all the metal material, titanium has no problem of allergization , inflammation , carcinogenicity and has excellent biocompatibility. In the year of 1940, Bother lead titanium into medical filed. In 2003, Yang Sefei, Guo Tianwen, (the Fourth Military Medical University) and Wang Youxu, Shan Zhifa, (Northwestern Polytechnical University) develop a special investment for zirconium-oxide titanium crown and bridge together. they selected zirconium-oxide and zirconite as the main stuff, as well as the collosol adhesive was use to make the FUS-invest investment. The capability of the suspension isn't ideal because the refractory has too large specific weight. Furthermore, the thickness of the pollution layer was 85μm~105μm because it has too much Si in the stuff. The needle crystal layer diffused distribution in the titanium matrix. The depth was about 350μm. This has bad effects to the properties. This study took the investment above-montioned as groundwork, aim directly at problems above to enhance the properties of the titanium castings.Objective:To improve FUS-invest investment of titanium crown and bridge. To decreased the thickness of the reaction layer, and enhance the properties of the investment as well as raise the precision. To establish the base of making titanium crown and bridge in clinical.Methods:(1)High purity sand and powder of zirconium was selected as the main materials, at the same time it was expose to high temperature to ripening. Adhesive, which has comparatively large specific weight was use to enhance the capability of the suspension after the powder and adhesive was mixed. In our research, firstly, the ratios between sand and powder, powder and adhesive, adhesive and solidification were determined. Titanium castings were invested according to this proportion. Secondly, analyze the grain size distribution of the powder. Dynamic viscosity, density and pH value of the adhesive were measured on different days. Room temperature strength, high temperature strength and residual strength were observed. Thirdly, thermal expansion curves of the molds were plotted. The procedure of burning-off was established.(2)Component and thickness of the reaction layer was analyzed.(3)The accu acy of standard crown was measured. (4)The tensile strength, yield strength, elongation and elastic modulu of the castings were measured.Results:(1)The ratios between sand and powder, powder and adhesive, adhesive and solidification were determined by two-pale assay. Titanium castings were invested after the investment was made up according to this proportion. It was convenience and the fluidity of slurry was pleasing, When temperature was 900℃,high strength was acquired. Mold cavity was smooth. The castings'appearance was glossy with no crack. The surface of the castings showed bright, metal color after sand blasting. Particle size distribution was uniformity. The particle diameter was during 10μm-0.5μm, and the value of median diameter was 4.01μm. The fifty percent mean diameter was 2.69μm.The value of PH of binder was 2.5,dynamic viscosity 3.2～3.4 mPa·S,specific gravity 1.304 g/cm3. These values had no significant difference in 7 days. Room temperature strength,high temperature strength and residual strength of the mold were 4.45MPa,3.16MPa,1.86MPa. Thermal expansion curves of the molds were plotted. The procedure of burning-off was established. The self-developed improved investment was named the improved FUS-invest(2)10 mm×10 mm×1 mm titanium castings were casted with the improved FUS-invest investment. The reaction layer was not obvious by the metallographic examination. The layer with plenty of Si was hardly detectable. The needle crystal layer diffused distribution on the surface of the titanium matrix. The depth was about 55μm. Spectrum analysis showed that the contents of Si and Zr decreased as the depth increased. The microhardness, which obviously decreased from the surface to the matrix, tended to be equal with the hardness of the matrix after the depth reached 75μm from the surface.(3) Fifteen wax sheet pattern crowns were made by the method of drop wax. The thickness of the wall was 0.5mm,diameter of supine surface was 7mm,diameter of superficies inferia was 7.5mm,the height was 6.5mm. Four spots were marked on the patterns every 90°. Titanium crown were invested by the improved FUS-invest material. Force about 15N was exerted to the masticatory surface after the titanium crown was inserted. The distance from the edge to the shoulder was measured. The marginal fitness of 15 master casts of the standard crowns was adequate to the demand of clinic.(4)Four plate-shape titanium castings were made according to the standard mechanical property ratio by the improved FUS-invest investment. The value of tensile strength , elongation and elastic modulu are 491MPa, 11.45% and 24.7 GPa.Conclusion:It could be proved that the improved FUS-invest investment for pure titanium casting reacted little with molten titanium,The thickness of the reaction layer of the improved FUS-invest investment was decreased to 55μm from 85μm—105μm, which was the thickness before improvement. The marginal fitness of the standard crowns was adequate to the demand of clinic. Mechanical properties, such as tensile strength, yield strength and elastic module, were pleasing. The improved investment enhanced the properties of the artificial teeth made by titanium as well as widened the field of pure titanium restoration. It settled the base that dentists roundly made titanium prosthetic denture together with low cost.
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