Three-Dimensional Stress Analysis Of The Periodontal Ligament Of Fixed Bridge Abutment Under Static And Dynamic Loads By Finite Element Method

ObjectiveA three-dimensional finite element model of a human mandibular incisors fixed bridge has been established to investigate stress, strain and displacement distributions of periodontal ligament of abutments under static and dynamic loads so as to provide theoretical references of biomechanics for clinical application of fixed bridge.MethodsA normal human mandible was used as an anatomy foundation to build a three- dimensional finite element model of mandibular incisors fixed bridge with CT scanning aided model building. Finite element analysis was performed on the model under both static and dynamic loads. The stress, strain and displacement distributions and stress-time curves were analyzed to study the biomechanical behavior of periodontal ligament of abutments.Results1. Before the fixed bridge was applied, under vertical load, the high-stress region was near around the apical of periodontal ligament with mainly compressive stresses. Under oblique load, the high-stress region was near around the cervical of periodontal ligament with both tensile and compressive stresses. After the fixed prosthodontics, stress, strain and displacement distributions were similar with that when the fixed bridge is not applied. But the maximum stress, strain and displacement increased apparently. The stresses in periodontal ligament of each abutment are almost the same.2. The stresses in exterior surface of periodontal ligament were larger than that of interior surface, which indicated the cushioning-effect of periodontal ligament. This character ofperiodontal ligament under vertical load is more obvious than that under oblique load.3. The stress, strain and displacement distributions of periodontal ligament under dynamic load are same with static load. But the maximum stress, strain and displacement decrease apparently. The rate of change is between 50%-60%4. The periodontal ligament has time-dependent mechanical behaviour. The stresses in periodontal ligament came down at once or some time delaied after unloaded. It referred to the location of stress point on periodontal ligament.5. Some level of residual stresses in periodontal ligament was left after one mastication period. The residual stress in exterior surface of periodontal ligament was larger than that of interior surface; the residual stress before fixed bridge was applied was lower than that of after fixed bridge was applied.6. The stresses of periodontal ligament droped to zero at 1.75 seconds under vertical dynamic loads, which of time was twice as long as one mastication period; but the stresses droped to zero at 1.3 seconds under oblique dynamic loads, the time was 1.5 times longer than one mastication period.7. The stress-free time under oblique load is shorter than vertical load.8. The displacements and stresses of periodontal ligament under small-strain and large-strain assumptions have not significant differences. The maximum displacements and stresses of large- strain are slightly higher than that of small strain. The difference varies from 1.4% to 19.1%.Conclusions1. CT scanning aided finite element model building used with 3D model building software and finite element software is a fast, convenient, precise and integrated method.2. Fixed prosthodontics does not change the displacement, stress and strain distributions of abutment periodontal ligament and just makes the values increased.3. Periodontal ligament has good cushioning-effect, which under vertical load is more obvious than that under oblique load.4. The stress, strain and displacement distributions of periodontal ligament under dynamic load are same with static load. But the maximum stress, strain and displacement decrease apparently.5. The periodontal ligament has time-dependent mechanical behaviour during mastication.6. There is some level of residual stress left after one mastication period. The level of residual stress is related to the magnitude and the direction of load.7. The direction of applied load is one im...