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
Trauma from occlusion causes vascular changes in the periodontium with in 
Select and explain. 
A. 45 minutes, B. 60 minutes, C. 30 minutes, D. 10 minutes
C: 30 minutes
Answer: C: 30 minutes 
Explanation: None