Pediatric Dentistry · single question
A male teenager presents with a bilateral posterior open bite. Radiographs reveal ankylosis of primary molars. What is the most likely cause of the posterior open bite?
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Correct answer: D. Ankylosis of primary molars
Ankylosed primary molars are fused to the alveolar bone and cannot migrate occlusally with jaw growth. The surrounding alveolar bone and adjacent teeth continue to erupt/grow, but the ankylosed tooth remains submerged (infraocclusion). This creates a bilateral posterior open bite — the adjacent permanent teeth over-erupt to compensate, while the ankylosed tooth remains at a lower level, leaving an open bite in the posterior segments.
- A. CORRECT. Ankylosis prevents normal occlusal migration of the primary molar with alveolar growth, causing progressive infraocclusion and bilateral posterior open bite.
- B. Incorrect. Tongue thrust typically causes ANTERIOR open bite, not bilateral posterior open bite.
- C. Incorrect. Unerupted permanent teeth alone do not directly cause posterior open bite in this pattern.
- D. Incorrect. An amalgam overhang would not cause a bilateral posterior open bite pattern — this is not a recognized cause.
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