The aim of the present study is to assess the changes of palatal morphology among growing patients with different vertical facial growth patterns treated with rapid palatal expander.

Thirty-six patients referred to "Policlinico Agostino Gemelli" university hospital will be selected. The eligible criteria are posterior cross-bite, mixed dentition, skeletal Class I relationship and prepubertal stage of cervical vertebral maturation. The patients will be split into three groups according to facial divergency (hyper-, hypo-, normodivergent subjects). For each subject, digital dental casts will be recorded before and after treatment using an intraoral scanner. To evaluate two-dimensional maxillary arch changes, linear measurements will be done. To study comprehensively the palatal shape, a set of 240 landmark and semi-landmarks will be digitized on the palatal vault. Then, Geometric Morphometric Analysis (GMA) will be performed to compare morphological variations of the palate among different vertical facial growth pattern groups.

Inclusion Criteria:

• Caucasian origin;
• Mixed dentition stage;
• Angle class I or straight step or mesial step molar relationship in primary dentition;
• Skeletal class I (ANB angle between 0° and 5°);
• Vertical dimension evaluated on lateral cephalograms: SN^GoGn>37°: hyperdivergent, SN^GoGn<27°: hypodivergent, 27°<SN^GoGn>37°: normodivergent;
• Cervical vertebral stage 1 or 2 (CVS methods 1-2);
• Posterior cross-bite including deciduous or permanent teeth;
• Presence of good quality pre-treatment records (history, intraoral and extraoral photographs, oral scan, panoramic radiographs, and lateral cephalometric radiographs with reference ruler);
• Oral scan and photographs available for each subject 6 months after the beginning of the therapy;
• Signing the informed consent form.

Exclusion Criteria:

• Previous orthodontic treatment;
• Tooth agenesis or supernumerary teeth;
• Craniofacial abnormalities;
• Tooth impaction in the maxilla;
• Torus palatinus;
• History of dental trauma (avulsion and alveolar/jaw fracture);
• Refusal to sign consent form.

Skeletal class 1 growing patients affected by cross-bite, coming to UOC Dental Clinic, Fondazione Policlinico Agostino Gemelli IRCCS will be enrolled for this study.