2009 Volume 29 Issue 1 Pages 21-27
Gypsum-bonded investments have been widely used for dental casting. However, these investments could not be applied for titanium casting because of the decomposition experienced at high temperature. The purpose of this study was to investigate the application of experimental casting investment for titanium which was composed of gypsum as a binder and magnesium oxide (MgO) as a refractory material for titanium at a common casting process temperature of 700°C. Five kinds of investments (G-5, G-10, G-15, G20, G30) were experimentally prepared and used for this study according to the quantity of commercially available dental stone and MgO powder. Fundamental properties and titanium castings from them were also evaluated. All of the experimental investments took a long time to harden compared to commercial gypsum-bonded investments; however, the proper peaks were detected in each investment before and after firing. Fired strength was in the range of 3.4 to 6.2 MPa and G-5 had a significantly lower value than the others. All of the thermal expansion curves were similar, and the quantity depended on the amount of MgO. Although there were no remarkable differences for castability among investments tested, external defects were found in a few castings from G-5. On the other hand, the reaction between the mold and molten titanium seemed to be smaller than estimated. There were no significant differences in hardness during experimentation except for more than G-20. In conclusion, it was possible to apply experimental gypsum-bonded investments for the titanium casting technique, and G-10, with smaller compressive strength, showed good performance within the limitations of this study.
