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Radiology · single question

What is the key radiographic distinction between internal and external root resorption?

  1. Internal resorption appears as a symmetric, centered radiolucent enlargement of the root canal that remains centered on different angulated radiographs
  2. External resorption shows uniform widening of the entire root canal
  3. Internal resorption appears as an irregular defect along the root surface that moves with changing angulation
  4. External resorption cannot be visualized radiographically
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Correct answer: A. Internal resorption appears as a symmetric, centered radiolucent enlargement of the root canal that remains centered on different angulated radiographs

The key radiographic distinguishing feature: Internal resorption — the radiolucent lesion remains centered within the root canal and maintains the same relationship to the canal regardless of the X-ray angle (it moves WITH the tooth/canal on angled radiographs). The outline of the canal appears expanded and balloon-like. External resorption — the radiolucent defect appears to move AWAY from the canal on angled radiographs (it is on the external root surface and moves relative to the canal when the angle changes). External resorption appears as irregular, flame-shaped, or 'moth-eaten' defect along the root surface, and the canal contour is maintained (or appears superimposed over the defect on one projection).

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