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
First radiographic sign of periodontitis 
Select and explain. 
A. Wedge - shaped radiolucencies, B. Loss of crestal bone, C. No sign, D. Loss of lamina dura
D: Loss of lamina dura
Answer: D: Loss of lamina dura 
Explanation: None