Mandibular fractures following marginal mandibular resection (MMR) remain an unresolved issue. The aim of this study is to determine the regions where stresses are likely to concentrate following trauma to the mandible after Marginal Mandibular Resection (MMR), and to identify the potential locations of postoperative fractures. Additionally, the study aims to establish the minimum bone height that can best resist trauma, with the goal of reducing fracture incidence. Using finite element analysis (FEA), 13 mandibular models were created. MMR was performed with constant mesiodistal diameters but increasing vertical resection heights by 5 mm increments. Seven resections were made in the symphysis and six in the body. A force of 1000 N was exerted to the symphysis. The von Mises (VM), maximum principal (Pmax), and minimum principal (Pmin) stress values were evaluated. The results showed that a residual bone height of 18 mm or less in the symphysis and 17 mm or less in the body leads to fractures under trauma. Residual bone height is a critical factor in preventing iatrogenic fracture following MMR. If insufficient bone height remains after MMR, prophylactic internal fixation should be considered to prevent fractures.