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
Decalcification and discoloration of teeth occurs during orthodontic treatment due to: 
Select and explain. 
A. Acid etching, B. Poor oral hygiene, C. Leakage of cement around bands, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None