Purpose: To analyse, and compare using finite element analysis, the biomechanical properties of the 1.7 mm miniplate fixation against 2 conventional fixation techniques (2.0 mm bi-cortical screws and 2.0 mm miniplate) used in the mandibular sagittal split osteotomy. Methods: A 3-D virtual mandible model was constructed using images from CT scan. Sagittal split osteotomy was carried out virtually, and the fixation techniques were applied onto the model. 9 virtual models consisted of the 3 fixation techniques with mandibular movements of 3 mm setback, 3 mm advancement and 7 mm advancement were developed. Bite forces of 50, 75 and 100 N were applied for incisor bite simulation and 100, 200 and 300 N for molar biting force. Finite element analysis was carried out in Solidworks, and readings of stresses and displacement were recorded. Wilcoxon rank sum test was applied and P-value of 0.05 was set for statistical analysis. Results: In this manuscript the authors have compared 3 internal fixation techniques in mandibular sagittal split osteotomy. There was a statistically significant difference for both stress and displacement readings between the 1.7 mm miniplate, the 2.0 mm bi-cortical screws and the 2.0 mm miniplate for all mandibular movements. For the 1.7 mm miniplate vs 2.0 mm bi-cortical screws, the stress reading was (P = 3.063e−08, W = 314), and for displacement was (P = 5.811e−05, W = 282). For the 1.7 mm miniplate vs 2.0 mm miniplate, the stress reading was (P = 9.862e−4, W = 263) and for displacement was (2.05e−2, W = 235). Conclusion: The 1.7 mm miniplate has adequate strength to be used in mandibular sagittal split osteotomy, although statistically less rigid when compared to the conventional 2.0 mm miniplate and 2.0 mm bi-cortical screws, especially in larger movements.
The sagittal split osteotomy is a versatile technique used in Mandibular orthognathic surgery. There are many types of internal fixation techniques available to provide fixation following the mandible split. The choice of fixation is mainly on surgeon preference, and can range from bi-cortical screws fixation and miniplate fixation. This study used Finite Element Analysis to investigate biomechanical properties of three internal fixation techniques. A pre-operative CT scan of a patient's skull was used to develop a half fully dentate mandible computer model. A sagittal split osteotomy was performed on the computer model and all fixation techniques applied to the model. Finite element analysis was used to study the effect of different fixation techniques on various mandibular movements and force magnitudes. The results of this study have shown consistently that the bi-cortical screws fixation records the least stress and displacement in all simulation models. Stress is mostly concentrated in the inferior-distal screw for the bi-cortical screws fixation whereas the stresses in miniplates are generally dissipated in the connector region of the plate. The 1.7mm miniplate was the least rigid fixation. The stresses in surrounding bone of the fixations were variable for each technique. Miniplate fixations had higher bone stresses in the setback movement but lower with mandibular advancements. Within the limitations of the study, the application of bi-cortical screws has shown to be the most rigid fixation, although with increased stresses in surrounding bone at mandibular advancements. The 1.7mm and 2.0mm miniplates are less rigid than the bi-cortical screws but handled stresses within the ultimate yield strength. Stress The force per unit area applied to an object. Von Mises Stress The equivalent tensile stress used to predict the yielding of materials, when they are placed under loads from different directions.
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