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': 'First radiographic sign of periodontitis \nSelect and explain. \nA. Wedge - shaped radiolucencies, B. Loss of crestal bone, C. No sign, D. Loss of lamina dura', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]