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
Which of the following full thickness flap is contraindicated for endodontic surgeries: 
Select and explain. 
A. Triangular flap., B. Rectangular flap., C. Trapezoidal flap., D. Envelope flap.
C: Trapezoidal flap.
Answer: C: Trapezoidal flap. 
Explanation: As collagen fibers and blood vessels run parallel to the root, In trapezoidal flap more number if collagen fibres and blood vessels are cut in turn it delays healing.