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
For an unbounded amalgam restoration, what should be done before copal varnish is applied ? 
Select and explain. 
A. Dentine desensitiser is applied, B. Smear layer is left intact, C. Smear layer is modified, D. After removal of enamel smear layer only
A: Dentine desensitiser is applied
Answer: A: Dentine desensitiser is applied 
Explanation: The use of a dentin desensitizer over the prepared tooth structure before placing amalgam is generally recommended. 
The dentin desensitizer is rubbed onto the prepared tooth surface for 30 seconds and excess moisture is removed without desiccating the dentin.

Sturdevant's Art and Science of Operative Dentistry. Edition 6. Page: 417