en تخصصي Special مقالات اصيل Original Article <span style="font-size:12pt"><span style="line-height:150%"><span new="" roman="" style="font-family:" times=""><b>Background: </b>Bilateral sagittal split osteotomy (BSSO) is the most common procedure in orthognathic Surgey of mandible also in asymmetries. However, the methods of fixation are different. Few studies worked on asymmetric cases especially with the use of finite element analysis (FEA). We aimed to evaluate stress distribution of two different Fixation techniques in mandibular setback surgery in asymmetric cases using FEA.</span></span></span><br> <span style="font-size:12pt"><span style="line-height:150%"><span new="" roman="" style="font-family:" times=""><b>Methods: </b>A 3-dimensional model of asymmetric mandible was obtained. SSRO with modified osteotomy was simulated unilaterally and another side osteotomized as common .Then differential set back was done and rigid fixation of that modified side with miniplate and monocortical screws was simulated then rigid fixation of other side by different fixation technics include 2 or 3 bicortical screws. With the force of 132N and 300N on the occlusal surface of first molars, the Von Mises Stress (VMS) distribution was calculated.</span></span></span><br> <span style="font-size:12pt"><span style="line-height:150%"><span new="" roman="" style="font-family:" times=""><b>Results: </b>Stress distribution in threads of screws in use of three bicortical screws was higher than two bicortical screws (161%). VMS distribution in spongy bone of left ramus in use of three bicortical screws was higher than the use of two bicortical screws (78% difference). VMS distribution in cortical bone of mandible body in use of three bicortical screws was significantly higher than the use of two bicortical screws (1.3% difference) (<i>P</i><0.5).</span></span></span><br> <span style="font-size:12pt"><span style="line-height:150%"><span new="" roman="" style="font-family:" times=""><b>Conclusion:</b> The use of modified osteotomy and fixation with rigid fixation of two bicortical screws can create a more predictable and uniform stress distribution in mandibular setback surgery in asymmetric cases.</span></span></span><br> &nbsp; Sagittal split ramus osteotomy (SSRO), Asymmetry, Fixation techniques, Mandibular setback surgery, Finite element analysis (FEA) 33 45 http://wjps.ir/browse.php?a_code=A-10-795-18&slc_lang=en&sid=1 Saeedeh khajehahmadi 100319475328460017013 100319475328460017013 No Department of Oral and Maxillofacial Pathology, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran Abdolrahim Shams ShamsA@mums.ac.ir 100319475328460017014 100319475328460017014 Yes Oral & Maxillofacial Diseases Research Center, Mashhad University of Medical Sciences, Mashhad, Iran Hadis Tahami 100319475328460017015 100319475328460017015 No Student Research Committee, Mashhad University of Medical Science, Mashhad, Iran Amin Rahpeyma 100319475328460017016 100319475328460017016 No Department of Oral and Maxillofacial Pathology, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran