Objective: To evaluate the following null hypothesis: there is no difference in the coronal and axial expansion patterns in skeletal and dentoalveolar measurements using two different types of microimplant-assisted rapid palatal expansion (MARPE) Methods: Pretreatment (T0) and post- MARPE (T1) cone-beam computed tomography (CBCT) images of 32 patients (14 men and 18 women; mean age, 19.37) were analyzed. We compared two different types of MARPEs. The first type of MARPEs include maxillary first premolars, maxillary first molars, and four microimplants as anchors (U46 type, n=16) and the other include only maxillary first molars and microimplants as anchors (U6 type, n=16). Results: In the molar region of the U6 type, the amount of midnasal, basal, alveolar, and dental level transverse expansion was 2.64 mm, 3.52 mm, 4.46 mm, and 6.32 mm, respectively. whereas in the U46 type, 2.17 mm, 2.56 mm, 2.73 mm, and 5.71 mm were acquired, respectively. A significant difference was found in the posterior alveolar level expansion (P_alv), (p = 0.036) and posterior basal bone level expansion (P_basal), (p=0.043) between groups, showing a greater posterior skeletal and alveolar expansion in the U6 type. Conclusions: The U6 type showed a greater amount of posterior expansion at the alveolar and basal bone level, showing an almost parallel split compared with the U46 type. Both types of MARPE showed a pyramidal pattern of expansion in coronal view.

Keywords: microimplant-assisted rapid palatal expansion, maxillary transverse discrepancy, cone-beam computed tomography, bicortical engagement