A Research To Three-dimensional Finite Element Analysis Of All-ceramic Layered Structure Crowns With Different Components

With the improvement of people’s living standards, the requirementsfor teeth aesthetics and health are also increasing. All-ceramic crownswith perfect appearance, corrosion resistance, abrasion resistance, goodbiocompatibility get more and more favor from doctors and patients. Butwith the masticatory and complex environmental effects of stress cyclesrole, all-ceramic material fatigue damage will occur, the collapse ofporcelain crowns fall off and lead to restoration failure. Therefore, how toreduce the all-ceramic crown damage becomes an issue which is closelywatched by dentists.Finite element method(FEM) is an mechanical analysis method thatis using continuous and uniform elastomeric divided into finite elementsto replace its original synthetic elastomer body, and finally obtain anelastomer mechanical analysis. FEM is a method which is versatile,flexible, accurate.It can draw the stress and displacement of thedistribution to make the results more intuitive. FEM has become a veryeffective means of simulation and performance analysis.There are many factors could affect the life of all-ceramic crowns.It’simportant to select appropriate materials by stress changes in thedistribution of study materials,to reduce the collapse of porcelain anddissolved of binder leading to failure to restore. Hojjatie B used the finiteelement method to research different thickness and the direction ofloading about porcelain occlusal surface stress distribution, and foundthat loading direction is more important than porcelain occlusal surfacethickness. Layered structure all-ceramic crowns are more vulnerable to the interface stress concentration, thus easily lead to structural failurebecause of the many factors like different thermal expansion coefficients,elastic modulus, chemical bonding, and the production process.WangHuarong found various thickness of veneer and core in the structure ofdouble-layered crown has a great influence on the bending strength ofall-ceramic crowns. Other scholars believe that the tensile stress and thematerial itself elastic modulus related to the role of stress transfer.Thehigher elastic modulus core has make it bear more stress to reduce thestress and burden of veneer and dental tissue.This experiment is designed to study all-ceramic crowns stresswhich have the same thickness of decorative porcelain, ceramic substrates,the adhesive bond under the same circumstances, different elastic moduliof porcelain, ceramic substrate laminate-like structure. It also explores alaminate sample all-ceramic crowns structural stress distribution andselection of clinical cases, and provide a theoretical basis for clinicalapplication.Select a tooth with form of standards, no occlusal caries, no obviousabrasion from the mandibular first molar. This experiment use built-inmetal embedded in epoxy resin as positioning signs,scan three-dimensional specimens by using64-slice spiral CT,collate thetomographic image data in DICOM format, import mimics10.0softwareto reduce the three-dimensional point cloud data points, denoising,smoothing, stitching, refining, and ultimately get a three-dimensionalsolid model. Use engineering software CATIA V5to reverse generate aall-ceramic model with occlusal thickness2mm, crown edge1mm,all-ceramic crowns aggregation angle of12°, and model all-ceramiccrowns into two-tier structure in accordance with the clinical need,namely the inner core (thickness0.5mm) and outer veneer, an adhesivelayer is set to0.05mm, periodontal ligament0.2mm.Each part is in turn divided into three-dimensional model of grid cells with HyperMesh10.0software, ultimately obtain finite element model. In this study, the datamodel is set to a continuous, homogeneous, isotropic linear elasticmaterial. Each interface are not relative sliding interface when stress loadis applied between the various models, and constraints are fullyconstrained to the bottom of the alveolar bone.A static pressure of200Nload on the the distal buccal cusp1mm of the occlusal surface at an angle0°,45°,90°and get stress cloud of all-ceramic crowns by computersoftware,and obtained stress values in different veneer and core withlayered structure of all-ceramic crowns.The results demonstrate:The maximum primary stress of all-ceramic crowns are mainlyconcentrated around the loading point and the edge of the neck. Thestress gradually decreases from the center to the surrounding, themaximum primary stress suffered from90°to45°to0°graduallyincreases;90°stress group focused on the ipsilateral neck edge of tooth,45°and0°group focused on the contralateral side. This distribution isconsistent comparison of results with other scholars.The maximum primary stress of the veneer focused on the outsidesurface, and the stress decreases sharply from the surface to the inner. themaximum primary stress of the core is mainly concentrated in the innersurface of porcelain ceramic, the stress decreases from the inside tooutside.In the same group of veneer, the maximum primary stress of veneerdo not change significantly, the higher the elastic modulus of the corehas,the greater primary stress gets; In the same group of the core, thehigher the elastic modulus of the veneer has,the smaller main stress gets,so is the main stress of the core; with the increase of the force angle, themaximum primary stress of all-ceramic crowns’ veneer and core is reduced.The experimental results show that the VonMises maximum primarystress of veneer refers to the load stress and the elastic modulus ofveneer.The larger elastic modulus veneer get, the smaller its stress suffer.And the larger the elastic modulus veneer get, the stronger ability to resistdeformation of the material has.So a high modulus of elasticity of veneermaterial helps reduce the stress,strain and possibility of its collapseveneer. High elastic modulus of core withstands greater stress in differentgroups of core. High elastic modulus of the material is strong resistanceto deformability,which means that the material has a higher hardness.Therefore, high elastic modulus of the core can better resist bendingdeformation and share more stress.With stress transfer, elastic modulus of the core get higher,the morestress it bears,which can reduce the burden of the veneer and tooth. Inaddition, experiments show that with the increase of the loading angle,lateral force is gradually enhanced and significantly increase the level ofthe stress of veneer and core, increasing the probability of damage crown.Therefore, we can reduce the lateral force to extend the life of theprosthesis.Conclusions1.The veneer has a high modulus of elasticity, making it suffered asmaller maximum primary stress, so the maximum primary stress of thecore is also smaller;2.The core has a high modulus of elasticity, the maximum primarystress get greater, but it has no significant effect on veneer.3.Reducing the force angle so that the crown obtained lateral forceincreases, the maximum primary stress of the veneer and the core alsoincreases4.The high the elastic modulus material of veneer and core can be selected in clinic. And we can enhance the success rate of the prosthesisby reducing the cusp inclination, the stress of veneer and the possibilitiesof collapse veneer.