Effect of Periodontal Ligament in alveolar bone response to loading

Objectives: The periodontal ligament (PDL) is the medium of occlusal force transfer in the jaws, and its mechanical properties likely have an effect on masticatory strain dissipation in the skull. Current finite element modeling practices typically incorporate the PDL into models as a simplified structure.  However, the impact of interpreting results from a simplified PDL model is unclear. To inform skull models, experimental data were collected to evaluate the effect of PDL behavior specifically in regards to hysteretic recovery periods.  A more complete understanding of the interaction between alveolar bone and the PDL under load can inform accurate computational models of masticatory mechanics and help establish the level of structural detail required in development and testing of these models. Methods: Experimental strain analyses were performed on three previously frozen, fresh Sus scrofa crania. A vertical occlusal load at the Ldm¹ was applied cyclically at 2Hz with a maximum load of 1000N.  Surface bone strain data were collected using rectangular rosette strain gages bonded to the maxilla at the alveolar margin, root apex level and midfacial regions. After data were collected with the PDL intact, a direct tooth-bone interface was established using adhesive (cyanoacrylate) with properties comparable to cancellous bone; cyclical loading was repeated.  Results: With the PDL intact, an average 30% hysteretic strain loss was observed in the alveolar margin.  After PDL removal, comparatively little hysteresis (<6% strain loss) was observed in alveolar strain recovery. Hysteretic behavior was not observed at the remote gages in either load condition. Conclusions: These data show the PDL's viscoelastic behavior is reflected in loading response of the alveolar bone and that effects of the PDL are primarily local to the load application site.  These results support the inclusion of the PDL's unique viscoelastic properties in alveolar models.