Three-dimensional Finite Element Analysis On Stress Characteristics Of Maxillary Premolar With Different Endodontic Access Or Root Canal Instruments

ObjectiveTo establish a 3D(three dimensional)model of the human maxillary first premolar for mechanics analysis.This study compared the stress magnitude and distribution under conditions of three different endodontic access and three different extents of root canal enlargement,so as to provide effective references for the design of endodontic cavities and the selection of root canal files in clinical practice of minimally invasive endodontic treatment.Methods1.Establishment of 3D finite element model of maxillary first premolar:A defect-free adult maxillary first premolar with Vertucci type 2-1 root canal was selected,and the cross section images were acquired by CBCT scanning and then reconstructed in Mimics Research,a reverse engineering software.Then the software Geomagic was used for image refinement and the model of several parts of tooth was built in UG,finally the 3D finite element model was constructed in ANSYS as the basis of mechanics analysis.2.Design of three types of endodontic cavities for stress analysis;Based on the finite element model,the traditional endodontic cavity(TEC),single-hole endodontic cavity(SEC)and two-hole-connected endodontic cavity(TCEC)were designed,then each group was loaded with vertical force 200 N at central fossa and lateral force 200 N at buccal slope of palatal cusp respectively.The stress nephogram and the maximum stress value of different parts of the tooth were obtained in the software,and the statistical analysis was conducted accordingly.3.Design of three types of root canal preparation:The finite element method simulated the result of root canal preparation using three different files after TCEC,then each group was loaded with vertical force 200 N at central fossa and lateral force 200 N at buccal slope of palatal cusp respectively.The coronal morphology and mechanical properties of the treated tooth was established so as to analyze the changes of stress condition caused by different extents of root canal enlargement.Results1.The finite element model of the maxillary first premolars had a good similarity with the sample tooth and could simulate the mechanical properties of the tooth tissue as well as the root canal system effectively.2.In the three types of endodontic cavities design groups,the common stress concentration areas appeared at the loading area of occlusal surface,and the cervical dentin in load of lateral stress.Under vertical loading,the maximum stress on enamel tissue surface and dentine occlusal surface was:TEC>SEC>TCEC group with statistical significance.In the cervical and root furcation region of dentin,TCEC>SEC group,and had insignificant difference with TEC group.On apical dentin,the maximum stress in the TEC group was significantly lower than that in the other two groups(p<0.0001).Under 45° lateral loading,the maximum stress on the tissue surface of enamel and occlusal surface of dentin was:TEC>TCEC>SEC group(p<0.001);On occlusal surface of enamel,the maximum stress of the TCEC and SEC group showed no statistical difference,which was smaller than that of the traditional pulpotomy group.3.In the three groups with different extent of root canal enlargement,the maximum dentin stress in the cervical region was smaller in the Medium group than in the Small group and the Primary group(p<0.01),and there was no statistical difference between the Small group and the Primary group.There was no significant difference in the maximum stress of the rest of the dental tissue between the three groups.Loading with lateral force,the maximum stress value of the enamel tissue surface was:Primary>Medium>Small group;on cervical dentin was:Primary>Small group(p<0.01)and had no significant difference with Medium groupConclusion1.Combined with CBCT and reverse engineering technology,the finite element method was applicable to simple biomechanical analysis of tooth.2.When the occlusal surface of the maxillary first premolar was loaded with vertical force,the loaded area of the occlusal surface became a high stress concentration area.When the lateral force was applied,the loaded area of the occlusal surface and the side of cervical dentine facing stress loading direction became the stress concentration areas.3.SEC group,as the most conservative method group showed the best performance in retaining tooth resistance.TCEC group enlarged the stress on tooth with load of vertical force,and decreased the stress on tooth(except apical area)with load of lateral force,which suggested the advantage of TCEC.4.In three types of root canal preparation groups,stress concentrated on cervical dentine after prepared by Primary(07/25)file when compared with other two groups,while the stress distribution of the rest of the tooth had no obvious changes on the whole.These three preparation extents were relatively safe in consideration of the fracture resistance of the tooth.