Rapid Maxillary Expansion for Bilateral Posterior Crossbite with Severe Crowding Management: A Case Report

Background: Transverse maxillary deficiency with bilateral posterior crossbite frequently coexists with a substantial tooth-size–arch-length discrepancy. Rapid maxillary expansion (RME) reliably corrects the transverse problem, but the arch perimeter it adds may be insufficient to resolve severe crowding. Treatment planning therefore has to separate the two problems.
Materials and Methods: An 11.5-year-old girl presented with bilateral posterior crossbite, transverse maxillary deficiency and pronounced anterior crowding. A tooth-borne Hyrax expander was used and then left in place as a passive retainer. Clinically significant crowding persisted after transverse correction, and the maxillary first premolars were extracted before maxillary fixed appliance therapy. Persistent mandibular space deficiency led to extraction of the mandibular first premolars and placement of a mandibular fixed appliance.
Results: RME corrected the bilateral posterior crossbite and the correction was maintained clinically during retention. Expansion alone did not provide enough space for alignment. Staged extraction combined with fixed appliance therapy produced progressive relief of crowding and teeth alignment.
Conclusion: In growing patients with bilateral posterior crossbite and severe crowding, transverse correction and space creation should be planned as separate objectives. Residual space requirements should be reassessed after expansion and retention, before an extraction decision is made for each arch.