What anatomical landmark is most commonly used to locate the apex of the mesiobuccal root of a mandibular first molar?

For mandibular first molars, the apex of the mesiobuccal root is located approximately beneath the mesiobuccal cusp tip when viewing the tooth from the buccal aspect. This landmark is used clinically and radiographically to estimate root length and working length during endodontic procedures. The mesiobuccal root tends to curve distally in its apical third, but the coronal projection of the apex aligns with the mesiobuccal cusp tip. The central groove and buccal developmental groove serve as landmarks for fissure sealants and the mesiobuccal root entrance on the pulpal floor, respectively.