Three-dimensional-finite-element Analysis Of Fiber Post On Dentinal Stress Distribution Of The Root Of Maxillary Central Incisors

BackgroundIt is an essential restorative measure to restore the endodontically treated teeth andseverely defective tooth structure with internal post and core technique. There are twoconventional viewpoints: one is that posts have the retention function and support theupper restoration, the other is that posts spread the stress along the root wall, avoidingroot fractures. Successful repair of post-retain crown is affected by several factors,including residual tooth tissues, materials of post and core, the length of post, types ofcementing agents, occlusion force and direction, etc. In order to satisfy the function ofrestoration, the materials used for making post and core should have proper modulusof elasticity and flexure strength, favorable anti-corrosion and anti-fatigue capabilities,moreover, these materials must have the function to protect tooth tissues. Howeverthe early used metal post system possesses many disadvantages, such as easy to breakthe root and corrode, poor aesthetics. Along with the development of aestheticrepaired materials, non-metal materials possessing good biological compatibility, anticorrosion and excellent physical and mechanical properties have entered the dental field, thus fiber-reinforced post system comes into being. Now people have furtherunderstanding on the function of post, that is post have no function to strengthen root,what clinical workers pay attention to has changed and how to make more evendistribution of stress, how to protect roots and how to get the best repaired effect havealready become the current most attracted problem. For this purpose, it is necessary tomake a study on stress distribution of fiber post on root.ObjectivesThrough three-dimensional-finite-element analysis, this article studies andestablishes three-dimensional-finite-element models of maxillary incisor teeth of postand crown repairs, analyzes the influence of post of different materials, diameters anddepths on distribution of stress of repaired root so as to provide some valuableinformation for clinical work.Materials and MethodsPartⅠ1. Obtainment of Primitive Data for Modeling: Choose a complete good conditionmaxillary central incisor with the size as Chinese standards reported by WangHuiyun. After fixing the tooth, scan tooth from root to dental crown using the GEMEDICAL SYSTEMS (Light speed 16 rows CT), make the section vertical tolong axis with layer distance of 0.625 mm, totally produce 39 sectional sectionpictures and save them in a numerical order.2. Establishment of Three-dimensional-finite-element Models: Switch the 39 CTpictures into JEP format documents, introduce AUTO CADsoftware, use graphictools to draw out internal and external contour lines of tooth section, that is toproduce closed curve lines of the cross section, put the space curve lines into ANSYS, use solid modeling function to connect the introduced curve lines ofsection to rebuild the solid model of maxillary central incisor. At the same timebuild porcelain outer crown, Ni-Cr alloy base layer crown, quartz fiber-reinforcedpost, compound resin core, periodontal ligament, gutta-percha points and alveolarbone.3. Hypothesis of Experiment, Parameters of Material Mechanics and Conditions ofloading: Various materials for experiments are supposed as continuing and evenmaterials with isotropic property, and the bearing force, deformation of materialsis small. The type of border condition is set total control and alveolar bone isfixed. As concerning clinical simulated binding condition, loading type is staticloading at the point between 1/3 of crown and tongue and 1/3 of incisor toothbeing 100N and forming an angle of 45 degrees with the long axis.PartⅡ1. Utilization of Experiment and Established Post and Core Repaired ThreeDimensional Finite Models. Establish six kinds of post repaired three dimensionalfinite models respectively: Ni-Cr alloy post, titanium alloy post, gold alloy post,glass fiber-reinforced post, polyethylene fiber-reinforced post and quartzfiber-reinforced post.2. Defined Materials and Border Conditions: The Same with partⅠ3. Conditions of Loading: The Same with partⅠ4. Observation of Indexes: Observe Von Mises stress and the 1 st Principal Stress ofcervix 1/3 of root, middle 1/3 of root, cusp 1/3 of root, at the same time observethe distribution of stress of post and root section. PartⅢ1. Utilization of Experiment and Established Post and core Repaired ThreeDimensional Finite Models: Establish 3 quartz fiber-reinforced posts withdifferent diameters (1.5mm,1.8mm,2.2mm),and place them at 3 differentdepth: 3mm,4mm,5mm from root cusp. Totally establish ninethree-dimensional-finite-element models repaired with post and core.2. Defined Materials and Border Conditions: The Same with partⅠ3. Conditions of Loading: The Same with partⅠ4. Observation of Indexes: Observe the Von Mises stress of the root of tooth and thesection of post and root.Results1. Establishment of the three dimensional finite models of maxillary central incisor.Upon establishment, 53897 nodes and dots were produced and formed 42768tetrahedrons each of which has 20 nodes.2. There are no obvious differences of stress distribution of post in the 6 types ofmaterials. The pea.k value ofVon Mises stress is located at the labial surface of thedental cervix. The peak value of 1st Principal Stress is located at the lingualsurface of the dental cervix. The stress of Von Mises and the 1st Principal Stressreduce from the place of 1/3 of dental cervix to the place of 1/3 of root cusp.3. Six materials were used to repair the stress of root: quartz fiber-reinforced post＞polyethylene fiber-reinforced post＞glass fiber-reinforced post t＞cast gold alloypost＞cast titanium alloy post＞cast Ni-Cr alloy post. But the different is small.4. Six types of stresses of repaired post/dentin section: cast Ni-Cr alloy post＞casttitanium alloy post＞cast gold alloy post＞glass-reinforced fiber post＞polyethylene fiber-reinforced resin post＞quartz fiber-reinforced post. Thedifferent is large. 5. Comparison of different diameters: post/dentin section Von Mises stresses:diameter 1.5＜diameter 1.8＜diameter2.26. Comparison of different depth: post/dentin section Von Mises stresses: 3 mm fromroot cusp＜4 mm from root cusp＜5mm from root cuspConclusion1. It is possible to combine CT scanning technology with the method of finitemethod and apply it to the repair model of Establishment maxillary central incisorof three-dimensional-finite-element models has fine similarity.2. Use high modulus of elasticity materials to repair teeth can change the situation ofdistribution of tooth essential stress and can easily concentrate on the stress ofpost/dental section, thus making root easy to be broken.3. Lower modulus of elasticity post benefits even distribution of stress andprotection of root.4. In certain extent, the smaller diameter of fiber post, the smaller stress is. Smallpost should be selected for clinical use.5. In certain extent, the post was put deeper, the smaller stress is.