Whenever pure titanium or cobalt-chromium alloys is used for dental restorations, the phosphate bonded investment was essential for its heat-resistant property especially during the casting process. The chemical reaction of crystallization of such bonding material has determinant influenced，Especially the reaction exist interface between the metal and bonded core, which requires further elucidated. The purpose of these thesis is to investigated the feasibility influence that pure titanium has toward surface coating and die-cast patterning by using plastic patterns coated with oxidized magnesium or oxidized titanium, which are casting feasibility and influenced then invested and cast using phosphate bonded material. Where optical microscopic is used for observing metallurgical-phase. scanning electron microscope is used for observing micro-structure crystallized on the inner surface of casting mold with different coating conditions. The method of investment has been used the plastic ring, which is removed before placed into furnace oven and heated in a ring-less stage. The results from these research that to attain observed showed that may obtain fine cast while used titanium-spinel series investment, and the similar was happened while using phosphate bonded core with oxidized magnesium coating there was also observed excessive chemical interaction phenomenon on the surface, while using oxidized titanium coating. The similar phenomenon was also appeared that used phosphate-bonded process and more oxidized seriously that situation using oxidized titanium coating. According to observation from study showed that available while using phosphate-bonded investment with oxidized magnesium coating which may restrict to titanium with “P” ”Si” or “O” interaction.
