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

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.