Treatment effects of modified miniscrew-assisted rapid palatal expander and rapid palatal expander for molar distalization

Objectives To evaluate the treatment effects of the modified miniscrew-assisted rapid palatal expander (MARPE) and rapid palatal expander (RPE) with distalizers in patients with Class II malocclusion and maxillary crowding. Materials and Methods The sample comprised 28 skeletal Class I adolescents with dental Class II malocclusion and maxillary crowding of >4 mm who received nonextraction treatment. Fourteen patients were treated with a modified MARPE with distalizer (MMD), while another 14 patients were treated with a modified RPE with distalizer (MRD). Lateral cephalograms and study casts were taken at pretreatment (T1) and after expansion, distalization, and at the initiation of alignment (T2). Twenty-nine variables were compared using a Bonferroni-adjusted independent t-test and a Mann-Whitney U-test. Results From T1 to T2, the maxillary first molars in the MMD group exhibited distalization of 3.0 mm and 2.4 mm at the crown and root (P < .001) compared with 2.1 mm and 1.4 mm in the MRD group. However, no significant difference was found in distalization between the two groups. The first molars in the MRD group showed a significantly greater distal tipping of 2.8° than in the MMD group (P < .001). Conclusions Although both groups showed maxillary molar distalization, the MMD group had no distal molar tipping, while there was significant molar tipping in the MRD group. It can be useful to plan nonextraction treatment with maxillary expansion and molar distalization in patients with Class II malocclusion and a narrow maxillary arch.