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
The primary etiologic factor in the development of furcation defect is 
Select and explain. 
A. Calculus, B. Plaque, C. Cemental caries, D. Root infection
B: Plaque
Answer: B: Plaque 
Explanation: None