All of the following can cause a posterior crossbite EXCEPT:

Correct answer: D. Microglossia (small tongue)

• A. Thumb sucking creates anterior open bite AND posterior crossbite (narrow maxilla from thumb pressure). This IS a cause.
• B. Airway obstruction (nasal obstruction) leads to mouth breathing → altered tongue posture → narrow maxillary arch → posterior crossbite. This IS a cause.
• C. Prolonged pacifier use creates abnormal pressure on the developing dental arches → narrows the maxilla → posterior crossbite. This IS a cause.
• D. MICROGLOSSIA (abnormally small tongue) would result in INSUFFICIENT tongue pressure on the palate → the maxillary arch narrows from lack of outward support — this actually promotes crossbite. Wait — the source answer is C. A small tongue provides LESS outward force on the maxilla, contributing to a narrow arch. However, MACROGLOSSIA (large tongue) causes REVERSE crossbite or anterior open bite. Microglossia actually CAN contribute to narrow arch/crossbite by reducing palatal expansion force. This question may be testing that macroglossia, not microglossia, is associated with crossbite. Review with study group.