الفهرس 
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Abstract
The aim of the study was to evaluate the effect of different cortical bone thicknesses (0.5, 1, 1.5 and 2 mm), miniscrew insertion angles (30o, 60o and 90o) and force directions (horizontal and 30o oblique) on stress distribution on miniscrew and surrounding bone that may contribute in miniscrew success using finite element analysis. The three-dimensional finite element model consisted of three components: Miniscrew, cortical bone and spongy bone. The miniscrew solid modeling was created on Inventor professional version 8 with diameters of 1.8mm and length of 8 mm according to manufacturer dimensions (3M Unitek™). The cortical and spongy bone were modeled in the finite element package, The bone geometry was simplified and simulated as a parallelogram representing cortical bone (20 mm length x 20 mm width x 0.5, 1.0, 1.5, and 2 mm height) and spongy bone (20 mm length x 20 mm width x 14.5, 14.0, 13.5, and 13 mm height). Finally these components were assembled in ANSYS environment and complete osseointegration was assumed. The resultant deformations and stresses of the applied load were collected from the output of ANSYS program, and they were collected in tables and figures according to maximum values of total deformations (Usum), Von Mises stress (Svon) and compressive stress (S3) in Mpa at each specified element in the specified volume through a twenty four runs. The general steps to perform a finite element analysis can be summarized as follows : A. Construction of geometrical model (buildup of solid volumes). B. Suitable element type selection. C. Definition of the material properties. D. Mesh generation (nodes and elements generation). E. Application of load and boundary conditions. F. Obtaining the data of resultant deformations, stresses and strains. The results were tabulated and bar charts were gathered to present the outputs of the finished runs. The results showed that : 1. Whatever the insertion angle, increasing cortical bone thickness reduced exerted microstrain on bone.2. 60o inserted miniscrew generated much more strains on cortical bone than 90o and 30o inserted miniscrews. 3. Force direction has minor effect on bone strains, but horizontal force slightly generates more strains on cortical bone than oblique one. 4. In 60o inserted miniscrew, horizontal force generates about 45% more strains on cortical bone than oblique one.