A new biomechanical model of the mammal jaw based on load path analysis.

The primary function of the tetrapod jaw is to transmit jaw muscle forces to bite points. The routes of force transfer in the jaw have never been studied, but can be quantified using load paths--the shortest, stiffest routes from regions of force application to support constraints. Here we use load path analysis to map force transfer from muscle attachments to bite point and jaw joint, and to evaluate how different configurations of trabecular and cortical bone affect load paths. We created three models of the mandible of the Virginia opossum, Didelphis virginiana, each with a cortical bone shell, but with different material properties for the internal spaces: a cortical-trabecular model, in which the interior space is modeled with bulk properties of trabecular bone; a cortical-hollow model, in which trabeculae and mandibular canal are modeled as hollow; and a solid-cortical model, in which the interior is modeled as cortical bone. The models were compared with published in vivo bite force and bone strain data, and the load paths calculated for each model. The cortical-trabecular model, which most closely approximates the actual morphology, was best validated by in vivo data. In all three models the load path was confined to cortical bone, although its route within the cortex varied depending on the material properties of the inner model. Our analysis shows that most of the force is transferred through the cortical, rather than trabecular bone, and highlights the potential of load path analysis for understanding form-function relationships in the skeleton.