Torque Loss in En-Masse Retraction of Maxillary Anterior Teeth Using Miniimplants with Force Vectors at Different Levels: 3D FEM Study

Objective: This FEM study was conducted to quantify the amount of torque loss in maxillary anterior teeth by applying force vectors from different levels to the anterior retraction hook at various heights and comparing with that of molar anchorage system. Materials and Methods: Five 3D FEM models were constructed with force vectors at different levels: HOT-High Orthodontic Traction (13.5mm from archwire) to ARH(1)-Anterior Retraction Hook (5mm), HOT to ARH2 (8mm), LOT-Low Orthodontic Traction (8 mm) to ARH(1), LOT to ARH(2) and from conventional molar hook to ARH(1). Mini-implants were placed buccally between the roots of second premolar and first molar. Torque loss was calculated by measuring the displacement of the teeth at crown tip and root apex in two planes i. e. sagittal and vertical using Y and Z axis respectively in all the five models. The results were statistically analyzed by using Kruskal Wallis ANOVA and Mann-Whitney U-test. Results: HOT to ARH(1) showed that the anterior teeth moved bodily (p = 0.5127), followed by molar hook-ARH(1)(p= 0.0495*) which showed mild uncontrolled tipping. Whereas the HOTARH(2), LOT-ARH(1), and LOT -ARH2 models exhibited uncontrolled tipping with maximum torque loss in LOT-ARH(1) (p= 0.0001*). Conclusion: It can be concluded that bodily movement with very minimal torque loss was observed in HOT-ARH(1) model whereas the maximum torque loss was recorded in LOT-ARH2 model. Conventional molar anchorage group showed uncontrolled tipping with some amount of extrusion and anchor loss of posteriors.