Root canal of maxillary first molar difficult for instrumentation

# Root canal of maxillary first molar difficult for instrumentation is:
A. Mesiobuccal
B. Distobuccal
C. Distolingual
D. Mesiolingual

The correct answer is A. Mesiobuccal.

Mesiobuccal root has greatest distal curvature and is narrowest of all the three roots. It is flattened in mesiodistal direction. Sometimes, it contains a fourth canal. 

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