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': 'Following is not an external manifestation of enamel \nSelect and explain. \nA. Enamel tufts, B. Enamel lamella, C. Incremental lines of enamel, D. Enamel cuticle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Perikymata are transverse, wave like grooves, believed to be the external manifestations of Incremental Lines of Retzius. Enamel cuticle is a delicate membrane that covers the entire enamel of the crown of a newly erupted tooth but is probably soon removed after mastication. Enamel lamellae are thin leaf like structures that extend from the enamel surface towards DEJ.', 'role': 'assistant'}]