Evaluation of Stress Pattern Caused by Mini-Implant in Mandibular Alveolar Bone with Different Angulations and Retraction Forces: A Three-Dimensional Finite Element Study

The objective of the study was to evaluate the stress pattern in cortical and cancellous bones, periodontal ligament, and in the implant itself when a mini-implant (MI) is inserted in the inter-radicular space between mandibular first molar and second pre-molar at various angulations and different retraction forces.Methods: Finite element study was conducted with MI insertion at 30°, 45°, 60°, 75°, and 90° angulations in the mandibular posterior region (between second premolar and first molar). At these angulations, horizontal forces of 150, 200, and 250 g were applied to the middle of the MI head. von Mises stress values were then evaluated using the ANSYS software.Results: Highest von Mises stress values were detected in the MI itself, followed by cortical bone, cancellous bone, and periodontal ligament. The von Mises stress values in cortical bone were highest at 30° angulation and lowest at 90° angulation. In the cancellous bone, the stress value was found to be maximum at 90°. The von Mises stress values in the MI were lowest at 90°. In all four structures, as the load increased from 150 to 250 g, the von Mises stress values increased.Conclusion: The von Mises stress values in the cortical bone, MI, and periodontal ligament were found to be lowest at 90°. Placement of the MI at 90° appears to be an ideal angulation when applied with a horizontal load. Force range used is within clinically recom-mended levels; however, the increase in load causes an increase in the stress values.Keywords: Cancellous bone, cortical bone, finite element model, periodontal ligament, mini-implant