Three-dimensional Stress Analysis Of The Periodontal Ligaments Of Molar Fixed Bridge Abutments Under Dynamic Loads By Finite Element Method

ObjectiveA three-dimensional finite element model of a human mandibular molars fixed bridge has been established to investigate stress, strain and displacement distributions of periodontal ligament of abutments under transient dynamic loads so as to provide theoretical references of biomechanics for clinical application of fixed bridge. MethodsA normal human mandible was used to establish a three-dimensional finite element model of mandibular molars all-ceramic fixed bridge and the corresponding periodontal substances with CT scanning aided model building, AutoCAD software and ANSYS software. Finite element analysis was performed on the model under dynamic loads in varying directions and positions in a circle of mastication. The stress, strain and displacement distributions and stress-time curves were analyzed to study the biomechanical behavior of periodontal ligament of abutments. ResultsThe three-dimensional finite element model was good in geometry, which can serve for the needs of the three-dimensional stress analysis.0-0.10s, the largest values of the displacement of the periodontal ligaments were in the directions of occlusional-gingival. The vertical forces created a little even stress within the periodontal ligaments .The highest stress concentrated on the apical and the cervical of the periodontal ligaments. 0.10-0.20s, the largest displacement in buccal-lingual direction appeared in the lingual cervical of the periodontal ligaments when the forces changed to be oblique direction. The stress kept on accreting with alarger pace, which resulted in an extreme compress stress concentrated on the lingual cervical of the periodontal ligament. 0.20~0.875s, the stress decreased as soon as the forces stopped and there was little residual stress.The stress within the periodontal ligaments in the second circles was larger than that in the first circle.The rules of the distributing of the stress with more or less values within the periodontal ligaments caused by the forces in the same directions , varying positions are similar.Exception of the instance that the force loaded on the molar, the values of the stress within the periodontal ligaments of the molars was less than that with the periodontal ligaments of the premolar. Conclusions1.The method establishing the three-dimensional finite model using the CT scaling technology was convenient, credible.2. The vertical forces created a little even stress within the periodontal ligaments. The high-stress region was near around the cervical of periodontal ligaments with mainly tensile stress, and the high-stress region was near around the apical of periodontal ligaments with mainly compressive stress. Under oblique load, the high-stress region was near around the cervical of periodontal ligaments with both tensile and compressive stress. The different directions of the forces had more influence on the distribution of the stress than the change of the positions.3. There was some level of residual stress in periodontal ligaments after one mastication circle.4. The stress within the periodontal ligaments in the second circles was larger than that in the first circle.5. The stress on the periodontal ligaments of the premolars was more than that on the periodontal ligaments of the molars, which indicated that the endure ability of the premolars should be considered firstly in clinically.6. The destruction by the conjunct forces was less than that by the individual forces, which indicated that the balance occlusion should be established.