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
Why do direct filling golds have to be flamed before insertion into the cavity preparation? 
Select and explain. 
A. To remove contaminants, B. To make gold soft, C. To form oxide layer on the surface, D. All of the above
A: To remove contaminants
Answer: A: To remove contaminants 
Explanation: Proper desorption is a matter of heating long enough at a temperature that removes contaminants and in the case of powdered gold, that burns away the wax.
Ref:Phillip’s Science of Dental Materials ed 12 pg 414