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Endodontics · single question

Which of the following is NOT a valid way to determine the number of roots on a tooth?

  1. Cone-beam computed tomography
  2. Direct surgical or clinical visualization
  3. Radiographs taken at different horizontal angulations
  4. An apex locator
Show answer and explanation

Correct answer: D. An apex locator

  • A. CBCT provides three-dimensional visualization and is the most accurate imaging method for root and canal anatomy.
  • B. Direct visualization after flap reflection, or examination of an extracted tooth, definitively establishes root number.
  • C. Shifting the horizontal angulation (the SLOB/buccal object rule) separates superimposed roots and is the classic 2D method.
  • D. CORRECT — this is NOT a way to determine root number. An ELECTRONIC APEX LOCATOR measures the electrical impedance between a file in the canal and a lip clip to determine WORKING LENGTH — how far the file is from the apical foramen in a canal you have ALREADY located. It gives no information about how many roots or canals exist, and it cannot find canals you have not entered.

Note: SLOB rule: Same Lingual, Opposite Buccal. Shift the cone and see which structure moves with the tube head.

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