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
[{'content': 'Pin retained amalgam is not used in: \nSelect and explain. \nA. Where margins of restoration rest below the gingiva, B. Non vital teeth, C. Hypoplastic teeth, D. Vital teeth', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]