<prompt> Highest incidence of extra canal is seen in which tooth?Maxillary 1st PMMaxillary 1st molarMaxillary 2nd molarMandibular 1st PM  <response>: 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 microscopeDOM, approx. 90-95 cases show extra mesiobuccal canal MB2. 