Optimizing Maxillary Anterior Teeth Intrusion in Clear Aligner Therapy: A Finite Element Analysis of Attachment...

Maxillary anterior intrusion with clear aligner therapy remains biomechanically challenging and clinically unpredictable. This study aimed to evaluate the biomechanical response of anterior intrusion under different clear-aligner attachment configurations using a three-dimensional finite element model incorporating a quasi-dynamic canine anchorage system.

A patient-derived finite element model of the maxillary dentition was reconstructed from CBCT data. A 0.75-mm polyurethane aligner and composite attachments were modelled across five attachment configurations: posterior attachments only (GP1), posterior with lateral incisor attachments (GP2), posterior with central and lateral incisor attachments (GP3), premolar attachments only (GP4), and a canine anchorage group (GP5). Displacement-controlled intrusion was simulated at five incremental levels (0.5-2.5 mm). Outcome measures included vertical tooth displacement, Von Mises stress distribution in teeth, periodontal ligament (PDL) and alveolar bone, attachment deformation, inclination changes, and anchorage-corrected biomechanical responses.

Intrusion displacement increased progressively with activation across all groups (p < 0.001; partial η² = 0.991). GP3 produced the greatest incisor displacement across increments (0.46-2.28 mm), closely followed by GP5 (0.44-2.21 mm). Attachment-deficient configurations (GP1 and GP4) showed significantly lower displacement (0.32-1.62 mm). Peak tooth Von Mises stress increased from approximately 146 MPa at 0.5 mm intrusion to 312 MPa at 2.5 mm intrusion, with GP3 demonstrating the highest stress transmission and GP5 showing slightly reduced but more evenly distributed stresses. PDL stress gradients increased linearly with intrusion depth (R² > 0.99), while attachment deformation and engagement efficiency were highest in GP3 and GP5. Anchorage-augmented mechanics in GP5 redistributed loading toward the canines, increasing the Anchorage Stability Index and reducing excessive incisor stress peaks.

Attachment configuration and anchorage control substantially influence biomechanical efficiency during aligner-mediated anterior intrusion. Comprehensive anterior attachments maximize force transmission, while physiologic canine anchorage enhances load distribution and biomechanical stability. These findings provide biomechanical guidance for optimizing aligner protocols in deep-bite correction.