Finite element analysis (FEA), in which forces propagate through an object with known material properties, is a useful tool to study the links between form and function. A common application is investigating bite forces and stresses during feeding in extinct and extant animals. In such studies, teeth are usually modeled as a single material with either bone or enamel material properties. However, most animals have teeth composed of an enamel cap covering a dentine layer. Here, using reptiles as a study group, we compare models with a more biologically realistic amount of enamel to those with simplified teeth. We created lower jaw models of the extinct archosauromorph Macrocnemus bassanii and herbivorous dinosaur Erlikosaurus andrewsi, and the extant monitor lizard Varanus salvator. We created three different enamel reconstructions for each taxon, representing the range of relative enamel thickness seen in extant taxa. We compared these more realistic reconstructions with models in which the entire tooth was assigned bone or enamel material properties only. Our results demonstrate the sensitivity of FEA to tooth material properties and reveal in which cases simplifications can be used without significantly affecting model outputs. We further demonstrate a semi-automated method of reconstructing enamel layers that can be applied to future studies. Thickness reconstructions can be adjusted according to estimates using histological information, comparison with modern analogues, or extant phylogenetic bracketing.