Preadolescents’ Smile Outcomes after Two Different Orthodontic Treatments: Traditional Interceptive Therapy with Rapid Maxillary Expansion (RME)/Schwarz Plate and Clear Aligners

To compare preadolescents’ smile outcomes after two different orthodontic treatments: RME/Schwarz plate (RS) and clear aligners (CAs). A sample of 31 patients (13 M, 18 F, mean age 8.3 ± 1.2 y.m) treated with RS and a sample of 28 patients (12 M, 16 F, mean age 7.9 ± 1.1 y.m) treated with CAS were included. Pre-treatment and post-treatment records were taken before the treatment (T1) and at the end of treatment (T2). Seventeen variables were evaluated. Both therapies were effective in smile width increase (RS = p < 0.02; CAs = p < 0.04) and buccal corridor reduction (RS = p < 0.02; CAs = p < 0.04). The intragroup analysis showed in the RS group an increase of incisor gingival display (p < 0.02), overbite (OVB) (p < 0.04) alongside a reduction of overjet (OVJ) (p < 0.01). Conversely, the CAs group evidenced a reduction in incisor gingival display (p < 0.04) and OVB (p < 0.01) with an increase in C angulation (p < 0.02) and maxillary incisor inclination (p < 0.04). An intergroup comparison evidenced a greater improvement in smile width, smile index and buccal corridor in the RS group with respect to the CAs group (p < 0.02; p < 0.02; p < 0.03). CAs were more effective in the management of gingival display, incisor position, midline correction (incisor gingival display p < 0.01; maxillary incisor position p < 0.04; maxillary dental midline p < 0.02), with a better control of OVJ (p < 0.01) and OVB (p < 0.02). The RS approach resulted in a greater smile width and a reduction in buccal corridor with respect to the CAs. The CAs provided a better management of both gingival display and smile aesthetics.