Optimizing mandibular second molar mesialization: A comparative analysis of stress distribution and displacement using tie-back and temporary skeletal anchorage device-assisted mechanisms with a nonlinear finite element model.

Abstract

Introduction: This study aimed to determine the optimal approach for mandibular second molar (M2M) mesialization in mandibular first molar extraction patients under 3 distinct scenarios-corticotomy-assisted or nonassisted-by evaluating 2 mesialization techniques (temporary skeletal anchorage device [TSAD]) supported coil spring and tie-back). The finite element method was used to compare stress distribution and displacement patterns.

Methods: Six models were designed to simulate M2M mesialization. In the first 3 models (hook models), the force was applied using posted arches with tie-backs to the M2M hook. In the final 3 models (TSAD models), a force was applied using a TSAD placed between the canine and premolar teeth, employing power arms extending from the M2M with closed-coil springs targeting the molar's center of resistance. The tie-back and power arm mechanism was tested and compared alone (models I-IV), with mesial incision (models II-V) and circumferential incision (models III and VI). Both decreasing (200, 100, and 50 g) and continuous (200 g) forces were used along 3 s/steps. In the nonlinear analysis, the total and directional displacement (along the x-, y-, and z-axes) and von Mises stress values were measured.

Results: TSAD models exhibited greater tooth displacement across all 3 axes with crown and roots translated mesially while showing minimal distal tipping (2.27° × 10^-2 to 2.63° × 10^-2). In addition, these models demonstrated greater lingual rotation and more pronounced extrusion on the mesial side. In contrast, hook models primarily exhibited mesial tilting rather than uniform mesial translation, with approximately 7-fold less overall extrusion and half the amount of lingual rotation compared with TSAD models. Piezocision failed to accelerate tooth displacements in both models. TSAD models generated slightly higher stress on the molar tooth and alveolar socket. In TSAD models, mesial and circumferential incisions reduced miniscrew stress by nearly half.

Conclusions: TSAD mechanics enabled greater mesial translation with minimal distal tipping, whereas hook models exhibited more mesial tilting but reduced overall extrusion and rotation. TSAD models showed greater alveolar bone stress response. Circumferential incisions with TSAD anchorage minimized unwanted movements and alveolar bone stress response. Given the inherent limitations of the finite element method in fully replicating clinical outcomes, these findings should be interpreted with caution and validated through clinical studies.