This randomized clinical trial aims to evaluate and compare the effectiveness of the Quad Helix (QH) appliance versus Rapid Maxillary Expanders (RME) in treating posterior cross-bite in Egyptian children during the mixed dentition stage. The study will also assess patient comfort and pain levels associated with each appliance.

The study involves 20 orthodontic patients aged 9-12 years with posterior cross-bite. Group A will receive the Quad Helix appliance, while Group B will receive Rapid Maxillary Expanders. Evaluation will be based on orthodontic study models, clinical photographs, and various radiographs including CBCT. Treatment will continue until complete correction is achieved, followed by a 3-month passive retention period.

Inclusion Criteria:

1. Children aged 9-12 years in the mixed dentition stage
2. Presence of posterior cross-bite due to transverse maxillary deficiency
3. No previous history of orthodontic treatment
4. Good oral hygiene and cooperative behavior
5. No significant antero-posterior or vertical skeletal discrepancies

Exclusion Criteria:

1. Patient with craniofacial anomalies
2. Presence of systemic diseases or syndromes affecting bone metabolism
3. Extensive dental caries or untreated periodontal disease
4. History of trauma or surgery affecting the maxilla or mandible

IPD will not be shared to maintain participant confidentiality and because the data is proprietary to the Orthodontic Department at Al-Azhar University.

It is an open-label study where both the participants and investigators are aware of the assigned intervention due to the nature of the orthodontic appliances used