This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Titanium casting is done 
Select and explain. 
A. Under vacuum in argon atmosphere, B. Under air pressure in nitrogen atmosphere, C. In specially fabricated aluminium vanadium crucible, D. Using CAD-CAM technique
A: Under vacuum in argon atmosphere
Answer: A: Under vacuum in argon atmosphere 
Explanation: Titanium has a high melting point (1668 °C) and high rate of oxidation above 900 °C. It requires a special casting machine with arc-melting capability and an argon atmosphere along with a casting investment consisting of oxides, such as MgO, ZrO2, or Y2O3, which are more stable than titanium oxide, to ensure acceptable castability.
Phillips 12th edition page 376