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': 'The formative cells of which of the following dental tissues disappear once tissue is formed \nSelect and explain. \nA. Enamel, B. Dentin, C. Periodontal ligament, D. Cementum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: When the enamel has fully developed, the ameloblasts cease to be arranged in a well-defined layer and is transformed to reduced enamel epithelium. The function of reduced enamel epithelium is protecting the mature enamel by separating it from the connective tissue until the tooth erupts. Premature degeneration of the reduced enamel epithelium may prevent the eruption of a tooth.', 'role': 'assistant'}]