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
A twenty year old female patient comes to the clinic with discoloration of the upper right central incisor. This tooth was intact and otherwise asymptomatic.

The common sequel following bleaching non vital teeth are: 
Select and explain. 
A. Ankylosis, B. Periodontal pathology, C. External cervical resorption, D. Reinfection
C: External cervical resorption
Answer: C: External cervical resorption 
Explanation: None