Maxillary and Mandibular Displacement Following Rapid Palatal Expansion

Objective: To examine the maxillary and mandibular responses to rapid palatal expansion (RPE) in all three dimensions. Methods: Twenty children (average age, 11.7 years) who required RPE treatment were included in this study. Pre- (T1) and post-RPE (T2) lateral and posteroanterior (PA) cephalograms, and study models were taken for all patients. For each patient, lateral and PA cephalograms at T1 and T2 were traced, and the sagittal, vertical, and transverse measurements were made. Also, on the pre- and post-expansion models, the widths between the first premolars, the first molars and the two acrylic halves of the Haas-type expander were measured. Results: From T1 to T2, the mean SNA increased 0.35 degrees (P < .05) and ANB increased 1.00 degree (P < .05). Both the ANS and PNS moved downward (1.30 mm and 1.43 mm respectively, P < .05) and the mandibular plane angle (MP-SN) increased 1.72 degrees (P < .05). The maxillary and mandibular incisors did not change significantly following RPE. After RPE, the mean increase of interpremolar width, intermolar width, maxillary width (J-J), nasal width, and interorbital width were found to be 110.7%, 104.5%, 30.1%, 23.1% and 3.3% of the screw expansion respectively. Conclusions: Following RPE treatment in children, (1) the maxilla displaced slightly forward and downward (P < .05); (2) the mandible rotated downward and backward (P < .05); (3) the widths of the maxilla and nasal cavity increased significantly; (4) the maxillary first premolars demonstrated significant buccal crown tipping.