Background/Objectives: Sagittal split ramus osteotomy (SSRO) is a widely used method in the treatment of mandibular deformities. However, high parafunctional forces associated with bruxism can negatively affect stability at the osteotomy site. Botulinum toxin A (BoNT-A), which reduces masseter activity, is considered an additional approach to controlling these forces. Methods: In this comparative finite element study, five different fixation configurations were created on a three-dimensional mandibular model and evaluated under identical boundary conditions using both a 1000 N bruxism-related parafunctional loading and a standardized force-reduction scenario. The stress distributions and displacement amounts on the cortical bone, screws, and plates were examined in each model. Results: The stress distribution was more balanced in the model with double plates, whereas the stress and displacement values were found to be greater for fixations with single plates and only bicortical screws. Under the standardized force-reduction scenario, lower stress and displacement values were observed across all the models. Conclusions: Among the evaluated fixation configurations, the double-plate model demonstrated the most balanced stress distribution. Under the standardized force-reduction scenario, lower stress and displacement values were observed across all the models; these findings reflect the load sensitivity of the fixation constructs and should not be interpreted as evidence of clinical efficacy.