The three-dimensional influence and clinical significance of anterior traction with rapid expansion during dental replacement

This study aimed to investigate the effects of rapid maxillary expansion using a Hyrax-type appliance (RME-Hyrax) with anterior traction on the maxillary arch during mixed dentition and its clinical significance, focusing on changes in arch dimensions, occlusal stability, and masticatory function. Forty-two patients with transverse maxillary deficiency were treated with RME-Hyrax, while an untreated control group of 40 received no treatment. Pre- and post-treatment dental casts were analyzed using a 3D scanner. Arch length, width, and occlusal stability were measured. Statistical analysis was performed using paired t-tests and linear regression. RME significantly increased maxillary arch widths at all measured points: 3CW: +4.06 mm, 4CW: +4.88 mm, 5CW: +4.09 mm, 6MCW: +3.00 mm (all p < 0.001). Mandibular arch widths similarly increased (3CW: +3.18 mm, 4CW: +4.00 mm, 5CW: +4.61 mm, 6MCW: +3.07 mm; all p < 0.001). Buccal movement of first permanent molars was significant in both arches (maxillary: 1.61-1.78 mm, mandibular: 1.52-1.68 mm; all p < 0.001). Occlusal stability improved clinically, evidenced by increased maximum bite area (+19.66 mm², exceeding the 15% threshold for functional gain; p < 0.001) and force (+1.06 kg, surpassing the 0.5 kg minimum meaningful change; p < 0.001), with reduced asymmetry index (-22.03%, p < 0.001). Masticatory efficiency improved from 54.22 to 84.61% (Δ30.39%, < 25% threshold; p < 0.001). Hyrax-type RME is effective for correcting transverse maxillary deficiencies, expanding both the maxillary and mandibular arches, and improving occlusal and masticatory function. Early intervention can significantly enhance dental and functional health.