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': 'Calcium hydroxide is used in deep cavities in order to: \nSelect and explain. \nA. Form dentin bridge, B. To kill microorganism, C. To cause necrosis, D. As a base under restoration', 'role': 'user'}, {'content': "Answer: A \nExplanation: A deep caries excavation close to the pulp, which may result in either an undetected pulpal exposure or a visible pulpal exposure, should be covered with a calcium hydroxide liner that can stimulate formation of dentin bridges (reparative dentin) over the exposure.\nIf used, the calcium hydroxide liner should always be covered with a glass ionomer or resin-modified glass ionomer liner before the tooth is restored.\n\nSturdevant's Art and Science of Operative Dentistry. Edition 6. Page: 83", 'role': 'assistant'}]