The Importance of Boundary Conditions and Failure Criterion in Finite Element Analysis Accuracy—A Comparative Assessment of Periodontal Ligament Biomechanical Behavior.

Featured Application: For a clinician, knowing the amounts of load that can be safely applied during a periodontal breakdown helps in improving the predictability of the orthodontic treatment and avoiding the ischemic and resorptive risks. Thus, knowing that an intact periodontium can bear up to 2.4 N without major ischemic or resorptive risks is of extreme importance. The 4 mm breakdown reference point, after which the applied loads should be lower than 1 N, supplies valuable data for both orthodontics and periodontology. The stress distribution areas displayed for each movement and bone loss level create a general complete image of PDL biomechanical behavior. For a researcher, providing a way to gain the much-needed results for dental studies with an accuracy comparable with those provided by the engineering field is valuable, since FEA is the only available method that allows the individual study of each dental tissue's component, and the current numerical studies have produced debatable and sometimes contradictory results. Thus, by employing the ductile resemblance material type failure criteria (T and VM) and linear elasticity, isotropy, and homogeneity/non-homogeneity as boundary condition assumptions in the study of PDL, the present study obtained results that are in agreement with clinical knowledge. Moreover, the above-mentioned boundary conditions are correct, up to an applied load of 2.4 N (with up to 1 N being acknowledged as mechanically correct). (1) Background: Herein, finite element analysis (FEA) of the periodontal ligament (PDL) was used to assess differences between Tresca (T-non-homogenous) and Von Mises (VM-homogenous) criterion, by simulating a 0–8 mm periodontal breakdown under five orthodontic movements (extrusion, intrusion, rotation, tipping, and translation) and three loads (0.6, 1.2, and 2.4 N). Additionally, we addressed the issues of proper boundary condition selection for more than 1 N loads and correlated the results with the maximum hydrostatic pressure (MHP) and available knowledge, evaluating ischemic and resorptive risks for more than 1 N orthodontic loads. (2) Methods: Eighty-one models of the second lower premolar (nine patients) with intact and 1–8 mm reduced periodontia were created. The assumed boundary conditions were isotropy, homogeneity, and linear elasticity. A total of 486 FEA simulations were performed in Abaqus. (3) Results: Both criteria displayed similar qualitative results, with T being quantitatively 15% higher and better suited. The assumed boundary conditions seem to be correct up to 2.4 N of the applied load. (4) Conclusions: Both criteria displayed constant deformations and displacements manifested in the same areas independently of the load's amount, the only difference being their intensity (doubling—1.2 N; quadrupling—2.4 N). Moreover, 2.4 N seems safe for intact periodontium, while, after a 4 mm loss (seen as the reference point), a load of more than 1 N seems to have significant ischemic and resorptive risks. [ABSTRACT FROM AUTHOR]