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
Calcium hydroxide is used in deep cavities in order to: 
Select and explain. 
A. Form dentin bridge, B. To kill microorganism, C. To cause necrosis, D. As a base under restoration
A: Form dentin bridge
Answer: A: Form dentin bridge 
Explanation: 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.
If used, the calcium hydroxide liner should always be covered with a glass ionomer or resin-modified glass ionomer liner before the tooth is restored.

Sturdevant's Art and Science of Operative Dentistry. Edition 6. Page: 83