In vitro micromechanical characterization of porcine periodontal ligament

Purpose: To evaluate some aspects of the experimental determination of the mechanical behavior of the periodontal ligament on porcine samples. The focus was on the mechanical properties of the periodontal ligament related to the presence/absence of fluid, and to the different position of the sample along the tooth root length. The application of these results could be used to develop computerized virtual models of the tooth-periodontium system. Methods and materials: Porcine mandibles were obtained from pigs (8–12 months old). From each one four blocks were cut, containing one complete inferior incisor and surrounding bone, then six sections were cut (each 2mm thick). Twelve samples were obtained from animals just suppressed and once sliced, put into a plastic container and immersed in physiologic solution. A testing chamber was built to apply tensile/compressive/shear displacements to samples in pressurized liquid. Inside the chamber a ±100N load cell was placed and a 100 cm long vertical tube allowing the application of a pressure when filled with liquid. The displacements were obtained through an endless screw activated by a servo-controlled motor. Preliminary tests were performed to determine the correct clamping method and the minimum non-slipping force of the grips. Tests were done at a constant displacement of 1mm/min. Experiments were done at room temperature (23 ◦C). Monotonic tension, compression, and shear tests, up to failure, have been performed and standard one-way ANOVA analyses was used (a=0.05). Results: Typical tension/compression and shear stress–strain curves were shown. Results in tension were substantially undisturbed by the presence/absence of liquid in the testing chamber. On the contrary, compression tests revealed a quite notable stiffness increase associated to the presence of pressurized liquid. It appears that only the shear mechanical parameters were correlated to the position of the sample along the tooth root. Conclusion: It is important to perform tests keeping the samples immersed in pressurized fluid. The most coronal sections seem to provide slightly higher strength values, as could be expected considering their proximity to the cementenamel junction.