Precision determination of the mechanical properties of the periodontal ligament in a combined numerical and experimental approach

Calculating initial tooth mobility using finite element analysis (FEA) requires exact knowledge of the mechanical properties of all materials involved and precise information on the geometries of tooth and alveolus. A wide range of values for Young's modulus of the periodontal ligament (PDL) can be found in literature, varying by a factor of 10(4), while the material parameters for teeth and bony structures have an uncertainty of a factor of approximately 10. Thus it was the objective of the presented study to determine nonlinear elasticity parameters describing the mechanical behaviour of the PDL regarding initial tooth mobility. In a first approach measurements were performed in segments of a pig's maxilla using a laser-optical set-up. From histological cuts of the specimens, FE-models were created semi-automatically using an especially developed mesh generator. Calculation of tooth displacements assuming linear material behaviour of the PDL resulted in large deviatons in the initial phase of the movement between theoretical and measured load/deflection curves. A bilinear behaviour of the PDL could be fitted to the experimental curves, giving a first Young's modulus of E-1 = 0.05 MPa below an ultimate strain of E = 7.5 % and a second one of E-2 = 0.22 MPa above this strain limit. These values could be verified aid of different load cases performed on six specimens in total.