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

Abstract

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.

Keywords: Class II; Crowding; Modified MARPE with distalizer; Molar distalization; Nonextraction.

Figure 1.

Typical designs and intraoral photos. (A) Modified miniscrew-assisted rapid palatal expander (MARPE) with distalizer (MMD; right side, during expansion; left side, during distalization). (B) Modified rapid palatal expander (RPE) with distalizer (MRD; right side, during expansion; left side, during distalization). (C) During MMD expansion and distalization. (D) During MRD expansion and distalization.

Figure 2.

Dental measurements. Po indicates porion; Or, orbitale; Pt, pterygoid; ANS, anterior nasal spine; PNS, posterior nasal spine; Go, gonion; Me, menton; U6, upper first molar; U4, upper first premolar; U1, upper central incisor; L1, lower central incisor; c, crown; r, root; FH, Frankfort horizontal plane (Po-Or); MP, mandibular plane (Go-Me); PtV, a line perpendicular to FH passing through Pt; PP, palatal plane (ANS-PNS); 1, PtV to U1c; 2, PtV to U4c; 3, PtV to U6c; 4, PtV to U1r; 5, PtV to U4r; 6, PtV to U6r; 7, FH to U1; 8, FH to U4; 9, FH to U6; 10, PP to U1C; 11, PP to U4C; 12, PP to U6C; 13, IMPA, MP to L1; 14, overjet; and 15, overbite.

Figure 3.

Skeletal and soft tissue measurements. S indicates sella; N, nasion; Po, porion; Or, orbitale; FH, Frankfort horizontal plane; EL, esthetic line; MP, mandibular plane; OP, occlusal plane; A, A-point; B, B-point; UL, upper lip; Sn, subnasale; Col, columella; LL, lower lip; Go, gonion; Me, menton; 1, SNA; 2, SNB; 3, ANB; 4, FMA (FH to MP angle); 5, FH to OP angle; 6, facial height ratio (S-Go/N-Me × 100%); 7, nasolabial angle; 8, UL to EL; and 9, LL to EL.

Figure 4.

Maxillary dental cast measurements. U4, upper first premolar; U6, upper first molar; 1, U4 width, distance between buccal cusp of right and left U4s; 2, U6 width, distance between mesiobuccal cusp of right and left U6s; 3, U6R rotation, angle between midpalatal raphe line (MRL) and line passing mesiobuccal and distobuccal cusps of right U6; and 4, U6L rotation, angle between MRL and line passing mesiobuccal and distobuccal cusp tips of left U6.

Figure 5.

Schematic drawing of mean treatment changes (mm) in the maxillary first molars, first premolars, and central incisors using a modified miniscrew-assisted rapid palatal expander (MARPE) with distalizer (MMD).