RESUMEN
ABSTRACT Objective: To evaluate how the lower arch spontaneously change after upper rapid palatal expansion in a group of patients with transversal skeletal deficit. Material and Methods: Twenty-four patients treated by the same orthodontist with a rapid palatal expander (RPE) bounded on a deciduous molar have been selected. The sample was divided into two groups: no treatment was provided for group one, while group two was treated using a lip bumper or Schwarz appliance. For each patient, dental casts were collected when the RPE was bounded (T0) and at the end of treatment, 9 months ± 3 months later (T1). Each outcome was analyzed, providing descriptive statistics, main effects significance tests and post-hoc analyses with the objective to evaluate the variations between pre-treatment (TO) and post-treatment (T1) of each of them. Results: If the linear measurements are considered, a significant beneficial effect on both arches is observed. However, the upper arch always shows a major increase of all values at T1 with respect to the lower arch. Even though the post-hoc tables indicate that time differences are all statistically significant across considered partitions, the lower arch's increase is more pronounced in group two, where patients were treated in both arches. If the angular measurements are concerned, the increase of lingual crown inclination was found in all patients, independently from the type of treatment in lower arch. Conclusion: All patients show normalization of upper diameters, regardless of whether the lower arch was treated or not.