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Endodontics · single question

What is the correct access cavity outline form for a mandibular first molar?

  1. Oval, centered in the occlusal surface
  2. Trapezoidal / rhomboidal
  3. Triangular with the base to the mesial
  4. Circular, centered over the distal canal
Show answer and explanation

Correct answer: B. Trapezoidal / rhomboidal

  • A. An oval access is used for premolars and anterior teeth.
  • B. Correct. The mandibular first molar typically has FOUR canals — mesiobuccal, mesiolingual, distobuccal, distolingual — arranged in a TRAPEZOIDAL (often described as rhomboidal) configuration. The access outline mirrors the canal orifice arrangement, placed in the mesial two-thirds of the occlusal surface. When only three canals are present, the outline becomes more triangular.
  • C. A triangular access with the base mesial describes the MAXILLARY first molar (three canals: MB, DB, palatal).
  • D. A circular access is used for anterior teeth (canines, incisors).

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