Three-dimensional Finite Element Analysis Of Early Cracked Maxillary First Molar With Restoration

ObjectiveThrough establishing three-dimensional finite element model of maxillary first molar with early cracked,the stress of each model was analyzed,so as to provide biomechanical theoretical basis for the restoration of early cracked teeth.Methods1.The images of maxillary first molar were obtained by cone beam computer tomography.Solid models were generated by Mimics,Geomagic and Solidworks software.2.Based on the solid model of maxillary first molar,Solidworks software was used to construct the cracked tooth model(group A).According to the repair form and materials,the models of resin inlay(group B1),porcelain inlay(group B2),resin onlay(group C1)and porcelain onlay(group C2)covering the mesial buccal and tongue tip,resin overlay(group D1)and porcelain overlay(group D2),zirconia crown(group E1)and resin filled zirconia crown(group E2)were established respectively.3.The meshes were divided in Ansys software and the material properties were assigned.Vertical and oblique loadings were applied to normal tooth,oblique loading was applied to cracked tooth and different restorations.Vertical loading was carried out in the direction parallel to the long axis of the maxillary first molar in the apex of the mesial and distal middle tongue,the central point gap and the mesial and distal marginal ridge,oblique loading was carried out in the direction of 45° to the long axis of the tooth in the middle of the lingual plane of the mesial and distal buccal apex,and the total load was 180 N.the equivalent stress,maximum principal stress peak and distribution characteristics of enamel and dentin were analyzed respectively.Results1.The enamel equivalent stress and maximum principal stress of normal maxillary first molar under vertical loading were concentrated at the occlusal loading point;dentin equivalent stress was concentrated at occlusal loading point,mesial and distal root with palatal root bifurcation,1/3 distal side of distal root,1/3 palate side of palatal root;the high stress area of maximum principal stress was located at the mesial and distal root with palatal root bifurcation.Under oblique loading,the enamel equivalent stress was concentrated at occlusal loading point,the maximum principal stress was concentrated at mesial and distal fossa sulcus and occlusal loading area.The dentin equivalent stress was concentrated on the 1/3 buccal side of the mesial and distal root and the buccal side of the enamelo-cemental junction,and the maximum principal stress was concentrated on the 1/3 buccal side of the palatal root and the palatal side of the enamelo-cemental junction.2.The peak values of equivalent stress and maximum principal stress of cracked tooth(group A)were higher than those of normal tooth,and the stress concentrated on the central point gap and the crack tip near the mesial surface.3.The stress of tooth tissue in each group after restorations:①The enamel equivalent stress of group B and group C was concentrated on the occlusal loading area,the high stress area of group D was concentrated on the buccal enamel and the enamelocemental junction,the equivalent stress of group E was concentrated on the enamelocemental junction.② The maximum principal stress of group B and group C was concentrated near the distal sulcus,the mesial surface of the buccal cavity,and the occlusal loading point.The maximum principal stress of group D was concentrated at the buccal side of the residual enamel,the mesial surface of the buccal cavity and the palatal of the enamelo-cemental junction.The high stress area of group E was located in the enamelo-cemental junction of the palatal side.③ The distribution of dentin equivalent stress and maximum principal stress was basically similar to that of normal tooth.The maximum principal stress concentration existed at the crack root of group A and group E1,while there were no stress concentration area in group B、group C、group D and group E2.④In the same restorations,the peak values of equivalent stress and maximum principal stress of group 1 were greater than those of group 2.Conclusions1.Compared with vertical loading,oblique load was more likely to cause cracked tooth.Under oblique loading,the mesial and distal sulcus of the maxillary first molar was the maximum principal stress concentration area,which was the predilection site of cracked tooth.2.Under oblique loading,the possibility of crack propagation in the maxillary first molar with early cracked was increased,and repair treatment should be carried out as soon as possible.3.Inlay、onlay and overlay could reduce the stress concentration at the crack tip of the maxillary first molar with early cracked.With the increase of the coverage area of the restorations,the possibility of crack propagation gradually decreased.4.For the same repair form,the resin material restorations with smaller elastic modulus would cause more stress to the tooth,so it was suggested to choose the porcelain material with high elastic modulus to reduce the stress concentration of the tooth tissue with residual crack.5.Crown could prevent crack propagation,but the crack should be removed during tooth preparation to prevent fatigue crack propagation during mastication.6.Zirconia crown restoration and full coverage porcelain overlay restoration of early cracked maxillary first molars could protect the remaining tooth tissue from the perspective of biomechanics.