Why is a triangular access outline used on a maxillary central incisor?

Correct answer: D. To remove the mesial and distal pulp horns

• A. The external crown outline is not what determines access design; internal pulp anatomy is.
• B. Post space is prepared later by removing gutta-percha; it does not dictate the access outline.
• C. Preserving the lingual marginal ridge is desirable for strength, but it is not the rationale for the triangular SHAPE.
• D. CORRECT. The pulp chamber of a maxillary central incisor is TRIANGULAR in cross-section, with a broad incisal base bearing two prominent PULP HORNS mesially and distally, tapering to an apex cervically. A conservative oval or round access leaves those horns unroofed. Retained pulp tissue in them degenerates and discolours the crown from within — the classic cause of a greying incisor after otherwise adequate treatment.

Note: Access design follows one rule everywhere: reproduce the shape of the pulp chamber at its widest cross-section, then achieve straight-line access to the canal orifices.