All of the following may contribute to the development of a crossbite EXCEPT:

Correct answer: C. Microglossia

• A. DIGIT SUCKING produces maxillary constriction alongside anterior open bite and increased overjet.
• B. Chronic AIRWAY OBSTRUCTION forces mouth breathing, which drops the tongue away from the palate and lowers the mandible. Without tongue support, unopposed buccinator pressure narrows the maxilla and produces a high vaulted palate with posterior crossbite — the classic 'adenoid facies' pattern.
• C. CORRECT as the EXCEPTION. MICROGLOSSIA is an abnormally SMALL tongue. Since posterior crossbite develops when the maxillary arch is too NARROW relative to the mandible, and normal tongue posture is what supports and widens the maxillary arch from within, a small tongue does not produce the constriction. MACROglossia is associated with mandibular prognathism and arch expansion — effectively the opposite problem.
• D. Prolonged PACIFIER use generates the same mechanism as digit sucking: the tongue is displaced downward while the cheeks apply inward pressure during suction, constricting the maxillary arch.

Note: The unifying mechanism for posterior crossbite is the loss of tongue support against buccinator pressure. This is why persistent mouth breathing warrants ENT referral — treat the airway, or the crossbite will recur after expansion.