When achieving endodontic access, the mesial surface of which tooth provides the most difficulty?

Correct answer: B. Maxillary first premolar

• A. The maxillary first molar is challenging for the MB2 canal, but that is a pulpal-floor issue, not a mesial-surface access problem.
• B. Correct. The deep mesial concavity of the maxillary first premolar (and the danger of a mesial strip perforation when locating two canals) makes access from/near the mesial the most difficult of these.
• C. The mandibular first molar mesial root has two canals but access difficulty is not driven by the mesial external surface.
• D. A mandibular lateral incisor is a simple single-canal access.