Which anatomical landmark on the occlusal surface of the mandibular first molar is used to locate the apex of the mesiobuccal root during endodontic treatment?

The buccal developmental groove of the mandibular first molar runs buccolingually along the buccal surface and aligns with the long axis of the mesiobuccal root. This relationship is used clinically to orient the endodontic explorer and locate the mesiobuccal canal orifice on the pulpal floor. Similarly, the buccal developmental groove can serve as a reference for the mesiobuccal root apex on radiographic assessment. Understanding the root trunk and root form relationships via occlusal surface landmarks helps minimize errors during access preparation and canal identification.