Effect of insertion angle on the stability of orthodontic mini-implants in a rabbit tibia model: A finite element analysis.

INTRODUCTION: Mini-implants are an alternative to traditional methods of anchorage in orthodontic treatment. However, there are still questions concerning their application, in particular, with the insertion angle. OBJECTIVE: To determine whether the angle of insertion of the mini-implant is a determining factor in their primary stability when they support orthodontic loads. MATERIALS AND METHODS: A finite element model (FEM) of tibia bone, spring and mini-implant was developed. The three-dimensional model of the rabbit tibia was constructed based on tomographic slices. The angles that were analyzed were 90 degrees , 80 degrees , 70 degrees , 60 degrees , 50 degrees , 45 degrees , 40 degrees , and 30 degrees . A horizontal force of 2 N applied to the head of the mini-implants was simulated. The von Mises stresses and displacements were determined using FEM. RESULTS: Von Mises stresses were lower for an insertion angle of 40 degrees followed by 90 degrees and 70 degrees ; likewise, the displacements of the mini-implants with respect to the spring were lower for the 40 degrees angle followed by 90 degrees and 70 degrees , we found a statistically significant association between the insertion angle and displacement. CONCLUSION: All mini-implants underwent a degree of angulation and displacement; however, mini-implants inserted to the bone surface at 40 degrees tend to have better primary stability, and they can withstand loads immediately.