[Casting accuracy and shrinkage of titanium castings made with zirconia investments]

To obtain inlay, crown and bridge types of titanium castings with sufficient size accuracy, zirconia investments with 10 mol % calcia were studied for their setting expansion, thermal expansion, total expansion, casting shrinkage compensation deficiency on fabrication method, particle size of zirconia, calcia and mixing liquid. Addition of calcia caused the change from contraction to expansion in setting and the additional thermal expansion at 900-1,200 degrees C. The choice of calcia and mixing liquid makes great influence on setting expansion, which is grouped into saturation type and delayed expansion type. By the use of the saturation type, total expansion could be controlled in the range of -2-(+)3%. Titanium castings of inlay, crown, bridge types with the values -2-(+)2% of casting shrinkage compensation deficiency could be successfully obtained. The casting shrinkage of titanium was estimated as 1.8-2%. The castings have the surface with a metallic brilliance as cast.