Which anatomic landmark on the occlusal surface is used clinically to approximate the location of the mesiobuccal root apex of a maxillary first molar?

Correct answer: C. The mesiobuccal cusp tip

• A. The central groove lies between the buccal and lingual cusps and overlies the pulp chamber floor region, not a specific root apex.
• B. The buccal developmental groove is a furcation-related landmark on the buccal surface, useful for locating the buccal furcation, not the root apex.
• C. CORRECT. The apex of a root lies approximately beneath the tip of its corresponding cusp. To estimate the mesiobuccal root apex, project a line apically from the MESIOBUCCAL CUSP TIP. This is used for approximating the injection site for supplemental infiltration and for orienting the radiographic beam over the root of interest.
• D. The mesiolingual cusp tip overlies the palatal root, which is the largest root and is positioned lingually.

Note: Cusp tip → apex of the corresponding root. Simple, and it comes up in anesthesia, endo, and radiology items.