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
Luebke ochsenbein flap is done in 
Select and explain. 
A. When marginal gingiva need to preserved, B. When Prosthetic crowns are present, C. To avoid non-pathogenic dehiscence, D. All the above
D: All the above
Answer: D: All the above 
Explanation: None