The Relation Between Bone Loss Of Mandibular Incisors And Stress Distribution Patterns With Three-Dimensional Finite Element Analysis

Once periodontal diseases occurred, alveolar bone loss would impair the ability of the tooth to resist different kinds of occlusal forces so that normal occlusal force could cause trauma of the periodontal tissue. The alveolar bone loss with vertical pattern would happen and the periodontal ligament space would be widened. From a biomechanics point of view, the distribution of stress on the inner wall of the alveolus of mandibular incisors with different bone heights was investigated in the present research to find when the changes of stress on the surface of the alveolar bone caused by bone loss would induce trauma of the periodontal tissue and further alveolar bone loss with vertical pattern.Part I Three-dimensional finite element analysis of the stress of mandibular incisors with bone lossObjective: To investigate the distribution of stress on the inner wall of the alveolus of mandibular incisors with different bone heights under different loadings.Method: A three-dimensional finite element model of mandibular incisor with normal alveolar bone height, named Model 1, was constructed. Then the alveolar bone of model 1 was lowered to respectively construct Model 2(Bone loss was one fourth of the root), Model 3(Bone loss was one third of the root), Model 4(Bone loss was the half of the root), Model 5 (Bone loss was the two third of the root) and Model 6 (Bone loss was the three fourth of the root). By three-dimensional finite element analysis, the von Mises stresses and the lingual displacement of each model were observed when different loading in 0, 15 or 30 degree was applied.Result: Under vertical loading, the maximum of stress of Model 1 was 13.171 MPa, located in the apical and the apical third region. The lingual displacement was 0.056mm. Under 15 degree oblique loading, its maximum was 14.315 MPa, located in the apical region. The lingual displacement was 0.197mm.Under 30 degree oblique loading, the maximum was 15.262 Mpa, located not only in the apical region but also on the crest. The lingualdisplacement was 0.324mm. From model 2 to model 6, with the reduction of bone height, the stress and the lingual displacement increased .The change of the stress was slowly in model 2 and model 3 (bone loss was less than the half of the root) . The maximum mainly distributed in the apical area or near the apical area. No stress concentration. The change of the stress was significantly from model 4 to model 6 (bone loss was not less than the half of the root). From model 4, the stress concentration began to happen on the crest.Conclusion: (1)The direction of loading can affect the value and the distribution of the maximum of the von Mises stress significantly. Compared to vertical loading and 15 degree oblique loading, 30 degree oblique loading is the most significant affecting factor, for its horizontal component is the highest among all kinds of loadings. (2) The bone loss will induce that the value of stress increased dramatically and the distribution of stress on the surface of alveolar bone changed. With the bone loss, the maximal stress began to concentrate on the crest instead of locating in the apical area. (3) When bone loss was less than half, the stress increased slowly. Once bone loss was not less than half, the stress increased significantly and stress concentration happened on the crest. Teeth were significantly mobile. Previously well-tolerated occlusal forces became traumatic. All of these would cause the further bone loss with vertical pattern. So it is indicated that when bone loss is not less than half, occlusal adjustment and splinting should be considered during the treatment of periodontitis in order to avoid the significant increasing of stress and reduce the destruction of periodontal tissues. Further clinical trials will be done to ultimately confirm this prediction.Part II Three-dimensional finite element analysis of the stress of mandibular incisors with bone loss under different levels of overbiteObjective: Periodontitis is caused by bacteria that colonize the gingival crevice...