Determination Of Modulus Of Elasticity Of Human Periodontal Ligament By Optical Measurement And Numerical Simulation

Objective:As an important tissue of the periodontium,PDL(periodontal ligament) is the most deformable component and the mainly responsible for tooth mobility. It transmits functional and orthodontic forces to the alveolar bone.It is believed that the resulting stresses or strains within the PDL and the bone control the bone-modeling process.Also with the development of modern stomatology,geometrical and biomechanical simulation model of stomatognathic system are widely applied in oral clinical and research work.Meanwhile,a higher simulating for the anatomy and biomechanical character of stomatognathic system are required greater.The present study was designated to develop finite element models presenting the same individual geometry as the respective human incisor,and determine the elastic properties of the periodontal ligament by measuring the initial buccolingual tooth displacements.The precise results can be used as instructions for orthodontic treatment.Materials and Methods:This study was carried out on eight human maxillary jaw segments containing central incisors.The segments were kept frozen at -20℃up to the start of the experiments.The specimens were first mounted in a block of resin to provide a stable fixation within the experimental setup of ESPI(Electronic Speckle Pattern Interferometry).Every maxillary incisor was experimentally translated so that stress or strain could be uniformly distributed in the PDL by applying a single force passing through the center of resistance. Displacements were measured under load using a laser sensing system. Force/deflection curves from the measurements were obtained.Subsequently finite element models presenting the same individual geometry as the respective autopsy material were developed by the software of Mimics and Ansys,based on the scanning data of the Micro CT,to simulate tooth mobility numerically under the same force systems as used in the experiment.The numerical force/deflection curves obtained from the models were fitted to the experimental curves by repeatedly calculating theoretical tooth deflections and varying the elasticity parameters of the human PDL.Results:1.The eight fine 3D(three-dimension) finite element models of the maxillary incisor with the PDL and alveolar was constructed successfully.After 3D meshing, the mean results of eight models have 115280 nodes and 80883 10-node-tetrahedral elements.The accuracy of the models was very high.The models can be observed from any view.2.A bilinear material parameter set was assumed to simulate tooth deflections.Mean values of E₁=0.04MPa,E₂=0.16MPa and an ultimate strain ofε₁₂=7.3 percent were derived for the elastic behavior of the PDL.Conclusion:1.On the basis of Micro CT images and the application of the advanced software of Mimics and Ansys,a complex 3D model can be reconstructed more precisely, which can reflect the real conditions.The model can also be used for CAD(computer aided design) or biomechanics analysis.2.Force/deflection curves from the measurements showed a significant non-linear behavior of elastic stiffness of the PDL.A bilinear material parameter set was suitably assumed to description of nonlinear properties of periodontal ligament.The non-linear characteristics of periodontal ligament should be considered in the future research,based on the advanced computerized system,in order to achieve more accurate mechanical simulation of the material characters.