Stress distribution patterns in mini-implant and bone in the infra-zygomatic crest region at different angulations: A finite element study

To evaluate, using the finite element method (FEM), von Mises stress patterns produced both in a mini-implant (MI) and the infra-zygomatic crest region (IZC) at different placement angles and force magnitudes. FEM modeling of an infra-zygomatic crest MI, of dimensions 2 mm × 12 mm, was designed and placed in the IZC bone. The MI was inserted at 50°, 60°, 70°, 80°, and 90° angulations to the IZC surface. Simulated orthodontic forces of magnitudes 8, 9, 10, 11, and 12 oz were applied to the MI head. Von Mises stress and magnitude both in the MI and surrounding bone were measured. Von Mises stress in the MI and bone was maximum at 90°. Least stresses were observed at 50° and 60° angulations. As force magnitude increased, von Mises stress increased linearly. Maximum stresses in the MI and bone were observed when loads were 12 oz and minimum stresses were observed at 8 oz. To achieve optimum primary stability, angles of insertion between 50° and 60° are recommended in the IZC region. Highest von Mises stress values were detected in the MI, followed by cortical and cancellous bone. Also, loading force between 8 and 12 oz exerted stresses below the tolerable threshold of bone and MI. Hence, proper placement of MI in IZC using these findings might provide better biomechanical stability during retraction and may help in preserving the bone-implant interface.