DEVELOPMENT OF DENTAL CASTING AND PORCELAINIZING TECHNIQUES FOR TITANIUM ALLOYS (CASTMATIC, ZIRCONIA, YTTRIA FACE COAT, MAGNESIA INVESTMENT, SODA-BORIC GLASS)

Titanium and its alloys are excellent metals for dental uses. Casting of titanium metals has been, however, difficult due to their high chemical reactivity at elevated temperatures. Thus, special melting and mold materials are needed.; The purpose of this study was to investigate molds, Ti alloys and porcelain applications, utilizing a new dental casting machine, Castmatic. It involved argon-arc melting and subsequent argon/vacuum pressurized casting. Special refractory oxides such as yttria or Zirconia A were utilized for a face coat under phosphate bonded silica investment. Studies of Ti alloys (Ti, Ti-6Al-4V, Ti-15V, Ti-20Cu and Ti-30Pd) involved metallography, phase identification (XRD), hardness, tensile tests and electrochemical corrosion tests. Preliminary porcelain studies included an experimental low fusing (750(DEGREES)C maximum) porcelain along with commercial low fusing porcelains. The bond was evaluated by three point bending tests and SEM/EDX observations.; The yttria face coat was inert, but lacked the necessary mechanical and thermal stability. The face coat, consisting of Zirconia A and zirconium acetate binder, was stable and resulted in less mold reactivity, good internal soundness, but slightly rough surfaces. Small dental castings were prepared successfully by the Zirconia A duplex face coat system, but needed some post-cast machining to fit.; The metallographs revealed quite large grains in the cast structure, than in the wrought forms. XRD analysis showed the quasi-equilibrium phases present. Hardness measurements of cast Ti metals showed U-type hardness distributions due to oxygen diffusion. The moduli of elasticity of cast Ti metals were similar to those of gold alloys. The strength of titanium metals could be increased by alloying. The formation of excessive intermetallic compounds, however, hindered this effect (Ti-30Pd). All of the cast Ti alloys examined showed strong passivity trends in the corrosion tests.; An experimental low fusing porcelain adhered to cast Ti metals via mechanical retention. The bond strength was 42% of that of a commercial dental porcelain fused to a Pd-Cu alloy. The higher temperature (850(DEGREES)C) caused chemical bonding to occur between the metal and porcelain. At temperatures exceeding 900(DEGREES)C, cast Ti metals were severely oxidized, preventing porcelain adhesion.