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
Cause of apical periodontitis is/are: 
Select and explain. 
A. Sequel of pulpal diseases, B. Wedging of foreign object between the teeth, C. High points in restoration, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Apical periodontitis (AP) may occur in a vital or nonvital tooth.
Causes of AP in a vital tooth:

Abnormal occlusal contacts
High points in restoration
Wedging of foreign object between the teeth
Traumatic blow to teeth (Eg: Concussion).

Causes of AP in a nonvital tooth:

Sequelae of pulpal diseases  
Iatrogenic
Apical extrusion of debris through apical foramen during RCT.
Pushing irrigants or medicaments or obturating material through apical foramen.