The Periodontal Tissue Remodeling Of The Mandibular Molar Under The Functional Loading

Periodontitis, dental caries and physiological atrophy are contraindications into lossof alveolar bone, changes in bone density and reduction of periodontal attachment whichmay potentially result in tooth loss. These diseases induce remodeling of alveolar bone inorder to adapt to the changes in the biomechanical environment. These changes occur asthe teeth and periodontal tissues cannot tolerate normal bite forces with reduced alveolarbone support due to Periodontitis. Excessive bite forces can lead towards continuousresorption of alveolar bone and consequentially tooth extraction. However, if appropriatebite forces are maintained, the resorption can be reduced. Therefore, it is very important tounderstand the remodeling of the periodontal tissues and evaluate its influencing factors inclinical practice.Bone, as a living tissue, has an ability to remodel itself to adapt its biomecha nicalenvironment and function by changing both its material properties and geometry (bone apposition or resorption) until new functional equilibrium is achieved. This phenomenonis called bone remodeling, which is associated mainly with density (internal) and/orgeometric (external) changes. Recently, there are many theories describing the boneremodeling process. For example, the process of bone remodeling is heavily influenced bymechanical loading conditions. If loading is excessive, bone’s self-repair mechanismscannot keep pace with the increasing damage and resorption will appear. Generally, boneremodeling can be defined as a process where bone gradually alters its morphology in anattempt to adapt to any new external loading. Many investigators propose that numericalsimulations and algorithms can be combined with finite element (FE) analysis to developquantitative numerical models for the prediction of bone remodeling. There have beensome investigations into the biomechanics of alveolar bone remodeling. Theseinvestigations were mainly associated with finite element (FE) analysis combined withmathematical bone remodeling algorithms to predict bone remodeling induced by dentalimplants. Nevertheless, there have been relatively few reports on mathe matical model forsimulating the remodeling process induced within natural teeth. There is limited study intobone remodeling and its influencing factors induced by natural teeth with differentperiodontal tissue attachment levels.This study incorporates three-dimensional (3D) FE models of the mandibular firstmolar with different levels of periodontal attachment. The stress distributions and bonedensity changes during the remodeling process of alveolar bone were investigated usingFE software ABAQUS and the material subroutine (UMAT). Strain Energy Density (SED)algorithms were applied to predict alveolar bone remodeling induced around natural teethwith differing levels of periodontal attachment under mastication loading conditions. Thisstudy’s outputs may be useful for diagnosis and treatment planning for periodontaldisease.All the study can be divided into four parts：1. The alveolar bone re modeling models of the mandibular molar with differinglevels of periodontal attachment we re established.Three-dimensional finite element (FE) models of the mandibular first molar with differing levels of periodontal attachment were established using reverse engineeringsoftware and the finite element analysis software. The FE software ABAQUS and the usermaterial subroutine (UMAT) based Strain Energy Density (SED) algorithms were appliedto establish the biomechanics models of alveolar bone remodeling.The results showed that the established biomechanics models of alveolar boneremodeling could better simulate the distribution of stress and density change of thealveolar bone. These results may be useful to investigate the remodeling process ofperiodontal tissue and evaluate its influencing factors.2. The effect of attachment levels on remodeling process of periodontal tissue of themandibular molar.The stress distributions, density and shape changes of the alveolar bone were analysedunder mastication loading using the established remodeling models of periodontal tissueand technical route to simulate bone remodeling.The results showed that the capability of alveolar bone to support dentition reducedwhen the periodontal attachment level was reduced. When the level of periodontalattachment was at the cement-enamel junction (CEJ) in normal position, extreme loadingwas420N. The resorption of alveolar bone was in the alveolar lingual ridge region androot apex area. When the attachment level was at the2/3of the root length, extremeloading decreased to300N. The resorption of alveolar bone was in the alveolar buccalridge region. And the attachment level to1/2of root length, extreme load ing was only240N, and the resorption of alveolar bone was in the root apex region.3. The effect of biting force on re modeling process of periodontal tissue of themandibular molar.The influence of loading magnitude on bone density and shape changes during theremodeling process of periodontal tissue of the mandibular molar were analysed using theestablished remodeling models of periodontal tissue and the technical route to simulatealveolar bone remodeling.The results showed that the alveolar buccal, lingual ridges and root apex areasexperienced higher stresses. The stresses and densities of the alveolar bone increased proportionally to increased mastication loading. Decrease in alveolar bone density underextreme loading indicated bone resorption. The remodeling rate was continual withgradual loading.4. The effect of loading time on remodeling process of periodontal tissue of themandibular molar.This research investigated the effect of loading time on the changes in alveolar bonedensity and shape during remodeling process under the corresponding extreme loadingusing the established remodeling models of periodontal tissue and technical route tosimulate alveolar bone remodeling.The results showed that the bone density increased gradually and then decreased afterthe equilibrium period of8months under extreme loading. The bone density at the rootapex region decreased most obviously. And the time when the alveolar bone absorptionwas shortened from24months to20months with the periodontal attachment levelreduced.Conclusion:1. The established remodeling models of the mandibular first molar with differing levelsof periodontal attachment in this study can better simulate the stress distributions, bonedensity and shape changes. The method of this study is feasible and the simulationresults are similar to the clinical situation.2. The capability of alveolar bone to support dentition decreased when the periodontalattachment level was reduced. The teeth with reduction of periodontal attachment dueto the excessive loading led to the density decrease in alveolar bone and boneresorption. The greater the load, the bone absorbed more obviously. When the level ofperiodontal attachment of the molar decreased, the bite force undertaken by the teethshould be reduced in the course of clinical treatment, in order to prevent from thedestruction and absorption of periodontal supporting tissue due to the excessiveloading.3. The remodeling speed of alveolar bone was quicker and the time of bone remodeling was earlier with the periodontal attachment level decreased. Therefore, the periodontalattachment loss should be focused at the same time the biting force undertaken by theteeth should be analysed during the clinical course of treatment, and early reasonableocclusion adjustment.