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': 'Which of the following structures is more permeable? \nSelect and explain. \nA. Enamel, B. Cementum, C. Coronal dentin, D. Radicular dentin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The vital dental pulp has a slight positive pressure that results in continual dentinal fluid flow toward the external surface of the tooth. Enamel and cementum, though semipermeable, provide an effective layer serving to protect the underlying dentin and limit tubular fluid flow.\nDentin permeability is not uniform throughout the tooth. Coronal dentin is much more permeable than root dentin.\nDentin permeability primarily depends on the remaining dentin thickness (i.e., length of the tubules) and the\xa0diameter of the tubules.\nBecause the tubules are shorter, more numerous, and larger in diameter closer to the pulp, deep dentin is a less effective pulpal barrier compared with superficial dentin.\nReference : Sturdevant operative dentistry 7th edition page no 9', 'role': 'assistant'}]