Thermal expansion typed investments for casting titanium.

New investments for titanium were developed by adding ZrC and ZrN as additives for thermal expansion to an MgO cement base investment with setting shrinkage and low thermal expansion. Setting, thermal and residual expansion, X-ray diffraction and compressive strength of these experimental investments, surface roughness of the cast plate and casting accuracy of titanium crowns were evaluated. Thermal expansion of investments increased with additive amounts, and residual expansion occurred even when cooling to room temperature after firing in an air atmosphere by the oxidation to ZrO2 of these additives. The casting accuracy of full-crowns cast into molds at room temperature correlated with the content of ZrC and ZrN. As the result the cast titanium crown could be obtained with low surface roughness and good adaptability.