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
Endodontic therapy is contraindicated for a single-rooted tooth that has: 
Select and explain. 
A. Discoloration, B. An acute apical abscess, C. A vertical fracture of the root and an associated deep periodontal defect, D. A horizontal fracture of the root and an associated deep periodontal defect
C: A vertical fracture of the root and an associated deep periodontal defect
Answer: C: A vertical fracture of the root and an associated deep periodontal defect 
Explanation: The vertical fracture of teeth has poorer prognosis, in addition to this presence of periodontal problem contraindicates root canal therapy.