Comparison of the effects of maxillary expansion applying rapid maxillary expanders or clear aligners in mixed dentition : A 3D finite element study.

Purpose: To compare maxillary expansion achieved through the use of a rapid palatal expander (RPE) or clear aligner systems (incorporating variable buccal and palatal attachments) during mixed dentition.

Methods: The study employed the ANSYS SpaceClaim (SpaceClaim Corporation, Concord, MA, USA) software for reverse engineering and computer-aided design (CAD) tasks, utilized the ANSYS workbench for model adaptation and mesh generation, and applied the LS-DYNA solver for the resolution of the finite element model. The posterior cap splint RPE, clear aligners with buccal attachments on teeth 55, 65, 16, and 26 (CAB), and clear aligners with palatal attachments on teeth 16 and 26 (CAP) were used in the study. The appliances were modeled based on two distinct scenarios: (1) an expansion of 0.2 mm per activation of the RPE splint or per aligner; (2) a total expansion of 8 mm. The results were evaluated using finite element analysis.

Results: In the first scenario (0.2 mm activation), maximum stresses on the first molars for the RPE, CAB, and CAP models were 47.649, 26.653, and 14.040 MPa, respectively. In the second (8 mm total activation) scenario, they were 1854.022, 665.629, and 559.368 MPa. Across all models, stress levels ranked in descending order at the Z point, PNS, ANS, and A point, with RPE showing the highest overall stress values.

Conclusion: The RPE induced greater stress (indicated by red zones) on the palatal region, particularly on the palatal and buccal surfaces of the buccal segments and on the gingival area of the incisors, compared to the other two appliances. Only the RPE group showed high stress distribution in the region of the midpalatal suture. Stress on the teeth was more pronounced following the RPE compared to aligners.