Effect of magnesia investments in the dental casting of pure titanium or titanium alloys.

For past several years, precious alloys have been gradually replaced by non-precious ones in the dental casting field because of the rising price of dental alloys. In Japan during the past ten years, nickel-chromium alloys have been used extensively for crown or bridge and porcelain-fused-to-metal restorations instead of gold or silver alloys. This tendency seems to be the same all over the world. However, the expanded use of nickel-containing base metal alloys in dentistry has raised questions concerning their biological safety, namely, carcinogenic and sensitivity risks.1) On the other hand, since pure titanium or titanium-based alloys have excellent biocompatibility, they have been applied as dental implants and bone screws or artificial joints in the orthopedic field. Titanium is considered to have following advantages over conventional dental casting alloys: (1) the specific gravity of titanium is about a half of nickel-or cobalt-based alloys, (2) the corrosion or tarnish resistance of titanium is excellent,