Which canal is MOST at risk for mesial perforation during root canal treatment?

Correct answer: D. Maxillary premolar

• A. The mandibular molar distal root is relatively straight — low risk of mesial perforation.
• B. Mandibular lateral incisors have narrow roots but the perforation risk is not specifically mesial.
• C. The palatal root of the maxillary molar is generally straight and large — low perforation risk.
• D. Correct. The maxillary first premolar has a significant root curvature, and both the mesiobuccal and distobuccal roots curve distally. Aggressive instrumentation without following the curvature risks 'stripping' or perforating the mesial aspect of the curved roots. The maxillary premolar is the highest-risk tooth for mesial perforation.