The Construcion Of The Three-dimensional Finite Element Model Of The Maxillary First Molar Root System

Root canal therapy(RCT) is the most fundamental and efficient way to cure endodontics and periapical diseases. In recent 20 years, the efficient rate of RCT is near 95% with the development of fundamental medical science research, new instruments, filling materials, preparation methods and operating microscope (OM). These developments also enlarge the range of tooth conservation and make the basis of the progress of the rehabilitation. RCT can be divided into 3 steps, including root canal preparation, root canal disinfection, and root canal obstruction, of which the canal obstruction is very important, for the treatment efficiency will be greatly affected with uncondensed or mislocated obstruction.The two common obstruction method include lateral pressure obstruction and vertical condensation method, both of which require considerable pressure to seal the root foramen and the collateral accessory root canal. According to former reports, with the high stress from lateral pressure obstruction, the gutta pertscha become the primary cause of tooth root diastema of pulpless teeth. However, recent findings show that the stress to tubal wall from lateral pressure is less than that from vertical pressure.Oral biomechanics is a science which using the views and methods of mechanics to study oral biology. It can help us to know the functions of oral system, prelude the change, bring forward new diagnosis and treatment and also make impersonality appraise. We can know the mechanics conditions of tooth tissue in tooth rehabilitation and RCT better using oral biomechanics.The Finite Element Method(FEM) is discretized to simple geometrical elements which are related to each other through nodal points. Application of the governing equations, loading and boundary conditions results in a system of equations which could be solved to find an approximate solution. Because finite element methods can be adapted to problems of great complexity and unusual geometry, they become an extremely powerful modern tool in biomechanics.Recent years, with the development of light, electricity and engineering techniques, tiny sample imaging become more and more important. micro-computed tomography(Micro-CT,μCT) is one of them. It has higher resolving power and definition. It is also good for medical treatment. With the exploitation of the software, It is possible to evaluate the features of root canal preparation in 3-dimensions.Aims and methods:1. To reconstruct a simulation model of post-preparation adult upper first molar root canal, and provide a new practical method for tooth morphology study.2. To reconstruct 3-dimension (3D) model of the human maxillary first premolar for biomechanics analysis. Scan a maxillary first molar after RCT with the Micro-CT, import the CT images to Mimics v8.1 software and prefabricate the 3D model. Then, after improvement, in the Geomagic 8 software and Unigraphics NX software, the model that can be identified by the FEA software is accomplished.3. To reconstruct three-dimensional finite element model for researches about oral biomechanics in the future. Analyze the influence of different cervical marginal type on the stress distribution of the maxillary first molar after RCT.4. To analysis the biomechanics on the tubal wall at times of lateral pressure obstruction and vertical condensation, with the previously established 3-dimension (3D) model.Results:1. The three-dimension (3D) model reconstructed by Micro-CT scan data objectively reflected the real contour and the pulp cavity figure of the tooth. After modification with the affiliated software, the structural demarcations appear more distinct. This model can reflect the real conditions without destroying the integrity of the specimen, with fine geographical and biomechanical resemblance to the natural tooth. So it is fit for clinical use. Moreover, this model can be observed in many different ways, including rotating, zooming and perspective.2. The fine 3D FEA model of the maxillary first molar after RCT was constructed successfully. After 3D meshing, the tooth has 244,360 tetrahedral elements, the pulp has 120,010 tetrahedral elements, in total, the total has 124,360 20-node-tetrahedral elements. The accuracy of the model is very high. We can differentiate the differences between the resin and the dentine on the Micro-CT image, but there are no notable differences between the enamel and the resin layer. It is hard for us to construct the 3D model of the resin layer.3. The model can reflect the real conditions. It also can make a basis to oral biomechanics in the future.4. Under vertical load, the lateral pressure obstruction showed the lowest Van mises stress, while the vertical condensation showed higher stress. Primary analysis showed that the stress to tubal wall from lateral pressure is less than that from vertical pressure.