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
[{'content': 'Highest incidence of extra canal is seen in which tooth? \nSelect and explain. \nA. Maxillary 1st PM, B. Maxillary 1st molar, C. Maxillary 2nd molar, D. Mandibular 1st PM', 'role': 'user'}, {'content': 'Answer: B \nExplanation: More than 70 percent of maxillary first molar has\xa0shown the occurrence of second mesiobuccal canal, and this is found to be the most common reason for retreatment of maxillary molars.\xa0\nIf seen through Dental operating microscope(DOM), approx. 90-95% cases show extra mesiobuccal canal (MB2).', 'role': 'assistant'}]