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
Highest incidence of extra canal is seen in which tooth? 
Select and explain. 
A. Maxillary 1st PM, B. Maxillary 1st molar, C. Maxillary 2nd molar, D. Mandibular 1st PM
B: Maxillary 1st molar
Answer: B: Maxillary 1st molar 
Explanation: More than 70 percent of maxillary first molar has shown the occurrence of second mesiobuccal canal, and this is found to be the most common reason for retreatment of maxillary molars. 
If seen through Dental operating microscope(DOM), approx. 90-95% cases show extra mesiobuccal canal (MB2).