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
Which of the following should be done in case of unbounded amalgam restoration before application of copal varnish? 
Select and explain. 
A. Applied after removal of smear layer only, B. Smear layer left intact, C. Smear layer is modified, D. Dentin desensitiser is applied
D: Dentin desensitiser is applied
Answer: D: Dentin desensitiser is applied 
Explanation: Sealing the underlying, prepared tooth structure is beneﬁcial for any type of restoration. For an  amalgam restoration, this can be accomplished without actually bonding the amalgam to the tooth.  
Nonbonded amalgams can have a sealed, prepared tooth structure through use of a sealer material  (such as Gluma Desensitizer) or a cured resin adhesive placed before the amalgam insertion.