Feeding-related forces are thought to act as selective pressures on the mandible and thus influence vertebrate mandibular morphology. However, while a large body of work exists on the biomechanics and structure-function relationships of mammalian mandibular morphology, results may not be fully applicable to sauropsids which exhibit unfused dentary symphyses and prominent intramandibular joints (IMJs), whose role in mediating or redistributing mandibular strain are not yet fully appreciated. Theropods, an ecologically diverse clade within Sauropsida with great diversity in mandibular shape, are thought to have possessed kinetic mandibles and mobile IMJs. This however presents a biomechanical paradox for large osteophagous theropods like T. rex that must use its adductors to both produce extreme bite forces and mediate possible excursions and wishboning of the dentary about the IMJ. We use finite element modeling (FEA) to investigate how the mandible of T. rex was biomechanically loaded under different hypotheses of symphyseal tissue properties and mandibular adductor orientation to examine the effect of symphyseal tissues and the IMJ on its mandibular performance. Our results show similar patterns of strain and deformation regardless of symphyseal tissue type. Inverse wishboning and long axis rotation about the IMJ induced by m. pterygoideus ventralis and m. adductor mandibulae externus medialis is best reduced by a dorsomedial orientation of m. intramandibularis that is contiguous with m. pseudotemporalis superficialis.