Stress Distribution in the Bone — Fixator System During External Miniplate Osteosynthesis of the Mandibular Bone

A.V. Kopchak, M.G. Krisрchuk

Abstract


A study of the stiffness, strength and reliability of the bone — fixator systems after mandibular osteosynthesis with titanium miniplates was performed by investigating the character of the stresses and strains distribution during masticatory loads using the methods of computer simulation. Three-dimensional finite-element model of the mandible segment with fracture in the angular region as well as the models of titanium miniplates and screws were created in the Solidworks software and imported into the Ansys 5.7 program for further calculations. The mechanical properties of bone considering its structural heterogeneity were applied on the base of experimental data. It was found out that under masticatory loads bone — fixator system was in a complex stress and strain state. Stress distribution was uneven: the greatest loads were noted in the first 2 screws from the fracture gap. Stresses passed on bone mainly in the area of the outer cortical plate, and their maximum concentration was observed in the area of the first 3–4 turns of thread. Increasing the number and length of the screws did not lead to a significant reduction of stress in areas of maximum concentration. Instead, the presence of contact between the bone fragments and the properties of the bone tissue in the fracture zone had a significant impact both on the distribution of stresses in the system, and their absolute value. In presence of interfragmentary diastasis all stresses were perceived and redistributed by plates and screws, their maximum value in conditions that meet soft food chewing exceeded the maximum allowable value and stability of the whole system was inadequate. If there was a direct contact between the fragments, compressive stresses in the region of the lower edge of the jaw bone were directly perceived by the fragments, which significantly reduced the plate load. Reducing the stiffness of bone near the fracture gap leads to increased strain of the system and increase the load on the screws remote from the fracture gap.


Keywords


mandibular fractures; surgical treatment; fixation; computer modeling; finite element method

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DOI: https://doi.org/10.22141/1997-2938.1.24.2014.82854

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