A pediatric patient presents with a unilateral posterior open bite. Radiographs and clinical exam show a submerged primary molar with a lack of vertical eruption and no periodontal ligament space around the roots. What is the most likely cause of the posterior open bite?

Correct answer: D. Dentoalveolar ankylosis of the primary molar

• A. Skeletal vertical maxillary excess produces an anterior open bite with a long-face pattern, not a localized posterior open bite.
• B. Thumb-sucking typically produces an anterior open bite, not a unilateral posterior open bite.
• C. A congenitally missing successor may lead to over-retention but doesn't produce a posterior open bite through submergence in the same way.
• D. CORRECT — DENTOALVEOLAR ANKYLOSIS of a primary molar (fusion of cementum/dentin to alveolar bone with no PDL) causes the tooth to 'sink' relative to normally erupting adjacent teeth, producing a localized posterior open bite (submerged tooth appearance). The classic radiographic sign is absence of the PDL space, and clinically the tooth has a high-pitched 'metallic' sound on percussion.