Three-dimensional evaluation of rapid maxillary expansion anchored to primary molars: Direct effects on maxillary arch and spontaneous mandibular response

Aim The purpose of this study was to evaluate the effects of rapid maxillary expansion (RME) on maxillary and mandibular arch in the mixed dentition. Methods Forty-four consecutive patients with transverse maxillary deficiency were recruited. Test group: 21 patients (10 male, 11 female; 7.4 ± 1.2 years) who underwent RME (Haas type) therapy banded on the primary second molars. Control group: 17 patients (10 male, 7 female; 7.3 ± 1.1 years old) who did not receive any orthodontic treatment. Dental casts obtained pre-treatment and after appliance removal (11 months) were processed by means of a three-dimensional scanner (3Shape D250 laser, DK). Digital landmarks were traced using the VAM software (Canfield Scientific Inc., Fairfield-NJ, USA). Arch Length, interdental width and torque differences were measured before and after the removal of the appliance. The t-test (P < 0.05) for paired data was applied to evaluate the measurements values before and after treatment. The linear regression model was employed to assess the correlations between treatment effects. Results The efficacy of the RME was confirmed both on maxillary and mandibular arch. Mandibular intermolar width (+2.02 mm) together with primary intermolar (+1.39 mm), intercanine width (+0.95mm) and torque variations significantly increased. The untreated control group showed no significant statistical differences between T0 and T1. The linear regression between maxillary and mandibular data showed correlations between the torque of the teeth 16/46 and 65/85 (P < 0.05). Conclusions RME anchored on primary molars is an effective treatment option to correct tranverse maxillary deficiencies. All the measurements increased significantly confirming the indirect effect of RME on the mandibular arch.