Importance of the variable periodontal ligament geometry for whole tooth mechanical function: A validated numerical study.

When mammalian teeth breakdown food, several juxtaposed dental tissues work mechanically together, while balancing requirements of food comminution and avoiding damage to the oral tissues. One important way to achieve this is by channeling mastication forces into the surrounding jaw bone through a thin and compliant soft tissue, the periodontal ligament (PDL). As a result, during a typical chewing stroke, each tooth moves quite substantially in its anchor-site. Here we report a series of experiments, where we study the reaction of three-rooted teeth to a single chewing event by finite element (FE) modelling. The nonlinear behaviour of the PDL is simulated by a hyperelastic material model and the in silico results are validated by our own in vitro experiments. We examine the displacement response of the complete tooth-PDL-bone complex to increasing chewing loads. We observe that small spatially-varying geometric adjustments to the thickness of the PDL lead to strong changes in observed tooth reaction movement, as well as PDL strain and bone stress. When reproducing the regionally varying thickness of the PDL observed in vivo, FE simulations reveal subtle but significant tooth motion that leads to an even distribution of the stresses in the jaw bone, and to lower strains in the PDL. Our in silico experiments also reproduce the results of experiments performed by others on different animal models and are therefore useful for overcoming the difficulties of obtaining tooth-PDL-bone loading estimates in vivo. This data thus enhances our understanding of the role the variable PDL geometry plays in the tooth-PDL-bone complex during mastication.