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 material is the most difficult to remove from the patient's mouth? 
Select and explain. 
A. Metallic oxide paste, B. Silicone impression material, C. Reversible hydrocolloid, D. Impression plaster
A: Metallic oxide paste
Answer: A: Metallic oxide paste 
Explanation: In dentistry, zinc oxide eugenol is popular as an impression material for making impressions of edentulous arches for the construction of complete dentures. It is classified as a rigid, irreversible impression material. It cannot be used for recording impressions of dentate arches and in areas of severe undercuts.
Mannapalli ed 3 page no 166