| ObjectiveTo evaluate the effect of the different endodontic access methods and the full-ceramic crown on the stress distribution in the maxillary central incisor by means of three-dimensional finite element analysis.Magnitude and distribution of the stress were observed to provide the theoretical direction for the choosing of the endodontic access method from the stand-point of the biomechanics and to provide the theoretical reference of the restoration methods as well.Materials and MethodsThe point cloud was obtained via the software Mimics by extracting the data from the CT database,and then the reverse engineering function in Creo was utilized to build the solid model of the maxillary central incisor.After that,four models were established based on the different endodontic access methods as well as the prosthetic treatments.The four groups were as follow.Group A:traditional access cavity preparation with resin filling.Group B:traditional access cavity preparation restored full-ceramic crown.Group C:minimally invasive endodontics with resin filling.Group D:minimally invasive endodontics restored full-ceramic crown.Two types of the load were applied as follow-1.Static load:A static force with magnitude of 100 N and at the direction of 45 degree with the long axis of the tooth was applied to the junction of the incisal section 1/3 and middle section 1/3.2.Dynamic Load:The force with magnitude of 100N and at the direction of 45 degree with the long axis of the tooth was applied on the edge of the maxillary central incisor at the beginning to simulate the chew force in a chew period,and the load was moved to the junction of the incisal section 1/3 and middle section 1/3 in 0.2s with constant speed.The pre-processing software Hypermesh was utilized to partition the model into the finite element mesh and to add the load and constraints.The models were then exported from the Hypermesh and imported to abaqus to perform the finite element analysis calculation.The maximum principal stress,the von Mises stress and the modified von Mises stress of the tooth tissue were investigated using the finite element analysis software.Results1.The analysis of static load:(a)For the models without crowns,the stress peaks of the maximum principal stress,the von Mises stress and the modified von Mises of group C were lower than those in group A.(b)For the models without crowns,in the cervical dentin of stress distribution,the stress concentration area of the von Mises stress and the modified von Mises stress in group C were smaller than those in the group A,and the stress concentration was weaker.(c)For the models without crowns,in the root dentin of stress distribution,the stress distribution of the von Mises stress and the modified von Mises stress in group C distributed more uniformly than those in group A,and the stress was transmitted to more region in the area of root apex.(d)For the models with crowns,the stress peaks of the both the maximum principal stress,the von Mises stress and the modified von Mises stress of group B were lower than those in group A,and the distribution of the stress didn’t change ob-viously.The stress peaks of both the maximum principal stress and the modified von Mises of group D were larger than those in group C,and the stress peaks of von Mises stress decreased a little,but and the distribution of the stress didn’t change obviously.2.The analysis of dynamic load:(a)The stress peaks of the maximum principal stress,the von Mises stress and the modified von Mises of all the groups were gradually decreased when the load position moved from incisal edge towards root direction.(b)In the total period of the load,the stress in Group A was larger than those in Group C.When the load was applied at the top of the pulp hole,the decreasing trended of the stress peaks of the maximum principal stress,the von Mises stress and the modified von Mises changed in the group A.The trends of the decrease of the stress peak became unobvious,and the stress peak gradually became larger than those in group C.The decreasing trend in group C was not obviously changed.(c)For the models with crowns,the stress peaks of the maximum principal stress,the von Mises stress and the modified von Mises of group D were lower than those in group B.The decreasing trends of the stress peaks of the maximum prin-cipal stress,the von Mises stress and the modified von Mises between group B and group D were the same,and no obvious change of the decrease trend were observed during the loading period.(d)For the models with the traditional access cavity preparation,before the load was applied on the resin,the crown restoration didn’t obviously influence the peak values of the stress.When the load was applied on the resin,the peak values in the model with crown was smaller than those without crown.(e)For the models with the minimally invasive access,the stress peaks of the maxi-mum principal stressand the modified von Mises of group D were generally larger than those in group C.The stress peaks of the von Mises stress of group D was lower than those in group C.(f)In the total period of the load,the von Mises stress,the maximum principal stress and the modified von Mises stress in group C had the smaller stress concentration areas than those of Group A,and the stress were distributed in more area in group C,which reduced the stress concentration.This phenomenon was especially obvi-ous at the begining of the load.The differences of the stress distribution between group B and D was not significant.Conclusion(1)For the maxillary central incisors without the crown,compared with the traditional ac-cess cavity preparation,the minimally invasive access reduces the stress and relieves the stress concentration.The minimally invasive access is superior than traditional access cavity preparation.(2)Due to the wedge effect in the traditional access cavity preparation with resin filling,the wedge effect results in the stress increasement.After the tooth was restored with full-ceramic crown,the crown eliminates the enlarging effect caused by the wedge effect.In the case of minimally invasive access,restoration with crown makes the stress distri-bution of the tooth more even and improves stress distribution.Furthermore,restoration with crown makes sure that the endodontic tooth has good long-term prognosis.Com-pared with traditional access cavity preparation with crown restoration,minimally inva-sive access with crown restoration is more suitable. |
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