A Study Of Mandibular Incisors-porcelain Laminate Veneers Complex Using The Three-dimensional Dynamic Finite Element Method

Bachground：Recently, with the constant improvement of the aesthetic consciousness,more and more people are seeking dentists for teeth cosmetic repair. As the mandibularincisors are the smallest human permanent teeth and the tissue for preparing is verylimited, especially for Asians, porcelain laminate veneer is more suitable than the fullporcelain crown. But in clinic, ceramic split and drop are the two common problemsfor porcelain laminate veneer. Scholars both at home and abroad have doing a lot ofresearch about the stress distribution of porcelain laminate veneer complex using thefinite element analysis method. However, few relevant reports on the mandibularincisors can be found.Objeetive：To establish the solid models of maxillary and mandibular incisors and thethree-dimentional finite element model of mandibular incisor-porcelain laminateveneer complex，which can lay the foundation for biomechanical analysis of theporcelain laminate veneer repair.To simulate the process of anterior teeth occluding and to study the stress andmovement of mandibular incisors-porcelain laminate veneers complex usingthree-dimensional dynamic finite element method. It can provide theoretical basis forthe application of the three-dimensional dynamic finite element method in oralbiomechanical analysis and for the clinical design and manufacture of the porcelainveneers.Methods：Three experiments were included in this study:Experiment1、 Establishment of the three-dimensional solid models of maxillaryand mandibular incisors using Micro-CT data. The adult’s maxillary and mandibular central incisors which had good configuration，without caries，defects，or obturatorwere chosen. All the teeth were extracted because of periodontal disease and theirlengths，widths and heights were close to normal average data. GE Explore LocusMicro-CT was used for scanning incisors. Mimics10.01software was used for readingtomography data of enamel，dentin，and medullary cavity，for data segmentation，and for3D reconstruction. Geomagic studio V9software was used for imitatingfilling-up hole and truing. Utilizing Catia V5R19software to complete3D solid modelthrough surface fitting and Boolean operation，integration of the enamel，dentine andmedullary cavity system.Experiment2、To establish the three dimentional finite element models ofmandibular central incisor-porcelain laminate veneer complex and to preliminarilyvalidate the validity of the model by static loading.Catia V5R19software was used tocut the solid model of the mandibular central incisor established in experiment1，simulating preparing the mandibular incisor. Boolean subtraction operation was forestablishing the porcelain laminate veneers and resin binder layers which were thenimported to ANSYS workbench software for meshing. The finite element model ofmandibular central incisor-porcelain laminate veneer complex and binder layer wasestablished. The process of anterior teeth occlusionon was simulated and static loadwas applied. Convergence test was done to validate the validity of the model.Experiment3、The application of dynamic finite element method in occlussalprocess of the mandibular central incisor-porcelain laminate veneer complex."Bondedcondition" was defined between the porcelain veneer and abutment.“Frictionlesscondition” was assumed between maxillary and mandibular central incisor-porcelainlaminate veneer complex. The dynamic force of150N was applied. The maximumequivalent von Mises stress in the mandibular central incisor-porcelain laminateveneer complex were set as output variables.The results were then comparied withthose of experiment2under static loading.Results：1. The three dimentional solid models of maxillary and mandibular incisorswhich contained enamel，dentin，medullary cavity，and alveolar bone were accurately reconstructed. All the models had favourable geometric similarities..2. The three-dimensional finite element model of the mandibular incisor-porcelain laminate veneer complex contained medullary cavity，dentin，enamel，binderlayer，porcelain laminate veneers，alveolar bone was accurately reconstructed。Modelswere composed of about771，788elements and551，587nodes. Model’s reliabilitywas conformed through convergence test..3. Dynamic load was more sensitive than static load in reflecting teethbiomechanics changes，under which the stress distribution of the teeth was more clearand reasonable and more similar to the physiological condition. Von Mises stress wasmainly concentrated in biting edge of porcelain veneers，the labial and lingualcervical shoulder of abutment. In the process of occluding，the stress in labial andlingual cervical region was increasing with loading time gradually.Conclusion：The modeling method using Micro-CT scanning data in combination withreverse engineering software Geomagic Studio V9，Catia V5R19and finite elementanalysis software Ansys14.0，is an effective way of establishing the three-dimensionalfinite element model of tooth tissue. It is quick、feasible and with high accuracy.Compared with the static finite element method，the dynamic finite elementmethod can simulate the process of occluding which is more silimar to thephysiological condition.The biting edge and labial and lingual cervical shoulder of themandibular central incisor should be designed and prepared to a reasonable shape，which can avoid stress concentration on porcelain veneers and abutments.