Orthodontics · patient case question
What is the diagnosis due to?
Patient case: Unilateral posterior crossbite
Scenario: The same patient — a profile photograph of the occlusion showing a UNILATERAL POSTERIOR CROSSBITE.
Show answer and explanation
Correct answer: D. Unilateral maxillary constriction
- A. Mandibular asymmetry can produce a crossbite but is a skeletal mandibular problem, less common than maxillary constriction.
- B. This is the more common clinical scenario and the answer keyed elsewhere in this same file: a BILATERALLY narrow maxilla causes premature cuspal contact, and the mandible SHIFTS laterally to achieve maximum intercuspation, producing an apparent unilateral crossbite.
- C. Unilateral mandibular expansion is not a recognised aetiology.
- D. Correct per the source key for this item. A TRUE unilateral crossbite results from an actual asymmetric narrowing of the maxilla on one side, with the mandible closing in centric relation without deviation.
Note: ⚠️ INTERNAL CONFLICT IN THIS FILE. Day 1 of this same recall keys the most common cause of unilateral maxillary crossbite as 'true maxillary constriction with collapsed bite unilaterally', while other files in the series key 'bilateral constriction WITH A SHIFT'. THE DECIDING TEST: check for a MIDLINE DEVIATION and a CR-CO discrepancy. If the mandible shifts on closure, it is bilateral constriction with a functional shift (far more common, and it must be treated early to prevent asymmetric growth). If there is no shift, it is a true unilateral constriction.