Abstract: The anatomy of maxillary first molar is complicated, and the variations of numbers of mesiobuccal canals, distobuccal canals, and palatal canals will increase in the difficulty of root canal therapy. This case presents a successful root canal treatment of a left maxillary first molar with five canals including two mesiobuccal canals, two distobuccal canals, and one palatal canal, assisted by opreating microscope and cone beam computed tomography (CBCT).

Key words: Maxillary first molar, Root canal system, Variation