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
Which of the following periodontal diseases does not have calculus? 
Select and explain. 
A. ANUG, B. Chronic adult periodontitis, C. Juvenile periodontitis, D. Periodontal abscess
C: Juvenile periodontitis
Answer: C: Juvenile periodontitis 
Explanation: None