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Pediatric Dentistry · single question

A male teenager presents with a posterior open bite and visible ankylosis of primary molars on radiographs/imaging. What is the reason for the posterior open bite?

  1. Ankylosis of the primary molars (an ankylosed tooth fuses directly to bone without a functional periodontal ligament, so it fails to erupt/move with the rest of the dentition as the jaw grows, effectively becoming 'submerged' relative to neighboring teeth)
  2. Excessive growth of the affected primary molars
  3. A normal developmental variant with no underlying cause
  4. Tongue thrust habit alone, unrelated to the ankylosis finding
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Correct answer: A. Ankylosis of the primary molars (an ankylosed tooth fuses directly to bone without a functional periodontal ligament, so it fails to erupt/move with the rest of the dentition as the jaw grows, effectively becoming 'submerged' relative to neighboring teeth)

An ankylosed primary molar is rigidly fused to the surrounding alveolar bone and cannot move/erupt along with the rest of the alveolar process as the jaw continues to grow, causing it to become progressively 'submerged' relative to adjacent teeth — when this occurs bilaterally or significantly in the posterior segment, it can produce a localized posterior open bite (infraocclusion) at the affected site.

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