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Radiology · single question

Which radiograph best evaluates the crown-to-root ratio?

  1. Occlusal radiograph
  2. Bitewing radiograph
  3. Panoramic radiograph
  4. Periapical radiograph
Show answer and explanation

Correct answer: D. Periapical radiograph

  • A. Occlusal films image the arch in cross-section and give no useful crown-to-root information.
  • B. The bitewing images only the crowns and the crestal bone. The apices are not on the film at all.
  • C. The panoramic film shows the apices, but its magnification is uneven — roughly 20 to 25% and varying by region and patient positioning — so measured ratios are unreliable.
  • D. CORRECT. Assessing crown-to-root ratio requires seeing the ENTIRE root including the apex, alongside the clinical crown, with minimal distortion. Only the PERIAPICAL film delivers that. Taken with the paralleling technique, it gives a dimensionally accurate image of the whole tooth.

Note: The ratios: 1:2 is ideal, 1:1.5 is acceptable, and 1:1 is the minimum for an abutment tooth. Remember that the ratio that actually matters clinically is crown to root within BONE, so a tooth with 1:2 anatomy but 50% bone loss has an effective ratio far worse than the anatomy suggests.

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