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  • Title: Biomechanical stress distribution on fixation screws used in bilateral sagittal split ramus osteotomy: assessment of 9 methods via finite element method.
    Author: Bohluli B, Motamedi MH, Bohluli P, Sarkarat F, Moharamnejad N, Tabrizi MH.
    Journal: J Oral Maxillofac Surg; 2010 Nov; 68(11):2765-9. PubMed ID: 20708317.
    Abstract:
    PURPOSE: The aim of this study was to assess the biomechanical stress tolerance of screws used in 9 fixation methods after bilateral sagittal split ramus osteotomy to determine which configuration leads to lesser force load on the cortical bone at fixation points. MATERIALS AND METHODS: A 3-dimensional computerized model of a human mandible with posterior teeth was generated. The bilateral sagittal split ramus osteotomy was virtually performed on this model. The separated model was assembled with 9 fixation methods: single screw, 2 screws one behind the other, 2 screws one below the other, 3 screws in an L configuration, 3 screws in an inverted backward L configuration, miniplate with 2 screws, miniplate with 4 screws, 2 parallel plates (upper + lower border), and square miniplate with 4 screws. Then, 75-, 135-, and 600-N vertical loads were applied on the posterior teeth of these models. The stress distribution on the screw sites on the buccal cortex was measured by the finite element method. RESULTS: In this model all the fixation methods withstood forces between 75 and 135 N. However, the single-screw and the 2-hole miniplate models showed that the stress distributions in the configurations were intolerable when 600 N of posterior force was applied. The results of this study indicated that the inverted backward L configuration with 3 bicortical screws was the most stable. CONCLUSION: Although this study indicated that the inverted backward L configuration with 3 bicortical screws was the most stable pattern, most of the patterns had adequate stability for clinical applications (mean, 125 N).
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