Three-dimensional finite element analysis of the influence of different stress modes in invisible aligners on anterior teeth retraction.

Abstract

Objective: To investigate the effects of different stress application methods of invisible aligners on anterior tooth retraction using three-dimensional finite element analysis.

Methods: An adult patient with maxillary protrusion undergoing orthodontic treatment with the extraction of the first premolars was selected for modeling. Five working conditions were simulated: ① Invisible aligner applying force for overall retraction of the maxillary anterior teeth; ② Invisible aligner combined with a micro - implant placed at the canine region's precise cutting site, applying a 1N force for overall anterior retraction; ③ Same as condition 2, with an additional 1 N force applied between the anchorage micro-implant near the maxillary central incisors and the aligner; ④ Invisible aligner applying a 1 N force at the canine region's precise cutting site for overall retraction; ⑤ Invisible aligner applying force combined with power ridge technology for root - controlled retraction of anterior teeth. Displacement and stress measurements-including displacement and stress at the coronal-radicular junction and periodontal ligament, as well as their components along the X (mesiodistal), Y (labiolingual), and Z (vertical) axes under different working conditions-were compared.

Results: Total tooth displacements were similar across all conditions (range: 0.23197-0.23276 mm), with conditions ③ and ⑤ showing slightly lower displacement, though differences were not statistically significant. Stress at the coronal-radicular junction varied between 63.298-63.964 MPa, with conditions ② and ④ exhibiting slightly higher values. Condition ⑤ demonstrated a slight reduction in junction stress (63.703 MPa), attributed to root - control technology. Periodontal ligament stress showed a gradual increase from 0.41426 MPa (condition ①) to 0.41634 MPa (condition ⑤), representing a minimal overall change. Displacement was predominantly along the Y axis (approximately 0.205-0.206 mm), with smaller movements in the X (0.055-0.056 mm) and Z (0.095-0.096 mm) directions.

Conclusion: All 5 working conditions produced comparable displacement outcomes, with condition ⑤ offering an advantage in reducing stress at the coronal-radicular junction, suggesting a benefit of root-controlled retraction in clinical application.