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: Surgery
The optimum length of screw for fixation of plates in mandible: 
Select and explain. 
A. 3 mm, B. 4 mm, C. 5 mm, D. 6 mm
B: 4 mm
Answer: B: 4 mm 
Explanation: Usually the thickness of buccal cortex is around 3.5 mm. A 4 mm length screw is adequate for proper screw-bone contact.