Effects of Invisalign Palatal Expander System

Inclusion criteria: 1. Mixed dentition phase with at least three nonmobile (stable) teeth which have more than 1/4 of primary molar root length left16 in either side 2. Early permanent dentition stage and early permanent dentition but second permanent molars not yet fully erupted in the arch 3. Unilateral or bilateral posterior cross bite patients; or Patients who have been diagnosed with transverse maxillary deficiency (Skeletal transverse discrepancy measured from the estimated center of resistances of the first molars17 ≤ - 3 mm); 4. Patients with Class I or Class II skeletal relationship 5. Subjects willing to consent to the trial Exclusion Criteria: 1. Any general medical health problems which may influence treatment 2. Any craniofacial anomalies 3. Skeletal Class III patients 4. Mixed dentition patients with more than 2 heavily restored primary second or permanent first molars.