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

The mesiobuccal root of the maxillary first molar is the most complex root in terms of canal anatomy — it frequently contains two canals (MB1 and MB2). The apex of the mesiobuccal root typically lies at or near the buccal developmental groove on the occlusal surface when projected. Clinically and radiographically, the buccal developmental groove serves as a reference for access cavity placement and radiographic angulation adjustments to visualize the separate MB1 and MB2 canals. Understanding root apex location relative to surface landmarks helps in working length determination and minimizes perforation risk.