Biomechanical analysis of interradicular and infrazygomatic miniscrew anchorage during two-step and en-masse retraction: A finite element study

The aim of this study was to evaluate the effects of interradicular and infrazygomatic miniscrew anchorages on tooth movement and von Mises stress distribution during two-step and en-masse retraction using three-dimensional finite element analysis. Eight finite element models were constructed combining two retraction mechanics (en-masse and two-step), two anchorage types (infrazygomatic and interradicular miniscrews), and two power arm heights (3 and 6 mm). A 150 g retraction force was applied along the line connecting the miniscrew and power arm. Static structural analyses were performed in ANSYS to calculate tooth displacement (x-, y-, and z-axes) and von Mises stress distribution. Stress was mainly concentrated in the cortical bone around miniscrew insertion areas, as well as on the lateral incisors and canines. Increasing the power arm height from 3 mm to 6 mm reduced uncontrolled tipping and extrusion, improving biomechanical control. Infrazygomatic anchorage produced less tipping and extrusion than interradicular anchorage in both mechanics. Two-step retraction generally showed slightly more controlled tooth movement compared with en-masse retraction. This finite element simulation showed that the two-step retraction approach with infrazygomatic anchorage and a 6-mm power arm resulted in comparatively reduced tipping and a more distributed stress pattern under the conditions of the present model. However, complete translational movement was not achieved in any model. As finite element models cannot fully replicate clinical conditions, these findings should be interpreted with caution and validated through clinical studies.