Endodontics · patient case question
Which anatomical landmark is used to locate the apex of the MESIOBUCCAL root of a maxillary first molar?
Patient case: Full-mouth series in a patient with several root-treated teeth
Patient: Male, 52 years old
Chief Complaint: New patient examination. Intermittent vague discomfort in the upper right quadrant.
Background: Several root canal treatments completed at different times by different clinicians.
Current Findings: A full-mouth radiographic series has been taken. On the periapical below, one root-filled tooth shows an obturation that stops well short of the radiographic apex, with a small periapical radiolucency (arrow).
Show answer and explanation
Correct answer: B. The mesiobuccal cusp tip
- A. The mesiolingual cusp overlies the PALATAL root — and the MB2 canal orifice is found in the groove running from the MB orifice toward the mesiolingual cusp.
- B. CORRECT. Each root apex of a maxillary molar lies approximately beneath its own cusp tip. The mesiobuccal cusp tip therefore overlies the mesiobuccal root apex — useful for angling a radiograph, for locating the apex during surgery, and for orienting the access cavity.
- C. The buccal developmental groove is a surface feature between the buccal cusps; it does not correspond to a root apex.
- D. The central groove runs between the cusps in the middle of the occlusal table and does not overlie any single root apex.