Effect Of changing various parameters on stress distribution in mini-screws and surrounding alveolar bone: a three dimensional finite element analysis

Abstract

The purpose of the study was to clarify and evaluate the effects of various force magnitudes and mini-screw length, diameter and insertion angle on the stress distribution of the mini-screw and the surrounding bone utilizing a three dimensional finite element analysis. Methods: We created a three dimensional finite element model simulating various clinical situations where mini-screws with different diameters (1.5 and 2 mm), lengths (9, 11 and 13 mm) and insertion angles (45 o and 90 o) were utilized under various force magnitudes (200 and 250gm). The resultant deformations and stresses from the applied loading were analyzed with a 3D FEM according to maximum values of total deformations and Von Mises stress. Results: The Von Mises stresses in both the mini-screw and the cortical bone in obliquely inserted 1.5 mm diameter screws with 200 gm and 250gm force were higher than those with 2 mm diameter screws. The Von Mises stresses in the spongy bone in both the vertically and obliquely inserted 1.5 and 2 mm diameter screws with 200gm and 250gm force were higher with the 2 mm diameter screws. The maximum compressive stress and equivalent micro-strain in cortical bone was evident with screw dimensions 13mm length and 2mm diameter under an oblique force magnitude of 250 gm. The Von Mises stresses in the spongy bone in obliquely inserted 1.5 and 2 mm diameter screws with 200gm and 250gm force were higher with the 2 mm diameter screws The maximum stress (Von Mises) generated in the miniscrew and cortical bone in all the simulated finite element models was 72.77 and 13.52 MPa respectively. Conclusion: Increase in the mini-screw diameter with both vertical and oblique insertion reduced the deformations and stresses within the mini-screw and cortical bone but increased the deformations and stresses within the spongy bone. Increase in the mini-screw length with vertical insertion had negligible effect. The deformation and stress values within the cortical bone were higher in oblique insertion than vertical insertion with both (200 and 250 gm) force.