A Three-dimensional Finite Element Analysis Of The Effect Of Minimally Invasive Endodontic Cavities On Stress Distribution Of Mandibular First Molar

Background:In order to get a better view,facilitate the treatment and improve the efficiency of infection clearance,in traditional endodontic treatment,plenty of healthy tooth tissues was removed,resulting in the decrease of fracture resistance.Studies have shown that even restored with full crowns,a considerable proportion of teeth were extracted because of tooth fracture.Recent years,in order to retain the normal function of teeth better and improve the long-term retention rate,some scholars have put forward the concept of minimally invasive endodontics.Preserving more peri-cervical dentin and important occlusive structures is key in MIE.Since the introduction of minimally invasive endodontics,many minimally invasive endodontic cavity accesses have been proposed.Among which the contracted endodontic cavity access is the most widely used in research and clinical practice.However,few studies have been conducted on the selection of coronal restoration after endodontic treatment in this way.No study has been conducted on the effect of PCD cutting on tooth resistance after RCT and the comparison between different minimally invasive endodontic cavity accesses.Objective:In experiment 1,three-dimensional finite element analysis was used to evaluate the effect of PCD on the stress distribution of endodontically treated mandibular first molar.In experiment.In experiment 2,three-dimensional finite element analysis was used to evaluate the influence of different endodontic cavities on the stress distribution of endodontics treated mandibular first molars.In experiment 3,three-dimensional finite element analysis was used to evaluate the effect of different restorations on contracted endodontic cavity access.Methods:1.A three-dimensional finite element analysis-the effect of PCD on the stress distribution of endodontically treated mandibular first molar: with the Micro-CT scan,Mimics software,Hyperwork software,3 models were established.Model A: An intact tooth;Model B: completely remove the roof of the chamber without PCD cut;Model C:completely remove the roof of the chamber with PCD cut.Simulation for direct resin restoration after endodontic treated.Under the constraint of alveolar bone fixation,the tooth hard tissue applied 600 N maximum bite force at different points of the crown,and daily chewing 225 N vertical,45 degrees oblique and horizontal loads.The maximum VM stress value and the stress distribution of models were analyzed and compared.2.A three-dimensional finite element analysis-the effect of different MIE cavities on the stress distribution of endodontically treated mandibular first mandibular molar: five models were established.Model A: an intact tooth,Model B: a contracted endodontic cavity model,Model C: a computer-aided design–based guided endodontic cavity model,Model D: a truss endodontic cavity model,Model E: a traditional endodontic cavity model.Simulation for direct resin restoration after endodontically treated.Under the constraint of alveolar bone fixation,the tooth hard tissue applied 600 N maximum bite force at different points of the crown,and daily chewing 225 N vertical,45 degrees oblique and horizontal loads.The maximum VM stress value and the stress distribution of models were analyzed and compared.3.A three-dimensional finite element analysis of endodontically treated mandibular first molar with contracted endodontic cavity accesses restored in direct and indirect method:Four three-dimensional solid model were established.Model A: tooth with contracted endodontic cavity restored by bulk-fill resin,Model B: tooth with contracted endodontic cavity restored by all-ceramic crown,Model C: tooth with traditional endodontic cavity restored by bulk-fill resin,Model D: tooth with traditional endodontic cavity restored by all-ceramic crown.Under the constraint of alveolar bone fixation,the tooth hard tissue applied 600 N maximum bite force at different points of the crown,and daily chewing 225 N vertical,45 degrees oblique and horizontal loads.The maximum VM stress value and the stress distribution of models were analyzed and compared.Result1.A three-dimensional finite element analysis-the effect of PCD on the stress distribution of endodontically treated mandibular first molar: three finite element models were established.Model A: an intact tooth model;Model B: a model with complete removal of the roof of the pulp chamber and no establishment of a straight path;Model C: a model with complete removal of the roof of the pulp chamber and establishment of straight path.The maximum VM stress value with vertical force: Model B> Model C> Model A,the maximum VM stress value with horizontal force : Model A>Model B>Model C,the maximum VM stress value with 45 °force : Model C>Model B>Model A,the peak of VM stress with the largest bite force: Model B>Model C>Model A.2.A three-dimensional finite element analysis-the effect of different MIE cavities on the stress distribution of endodontically treated mandibular first mandibular molar: a total of 5 3d finite element models were established.Model A: natural tooth model;Model B:guide plate type root canal access model;Model C: compact root canal access model;Model D: truss-type root canal access model;Model E: traditional root canal access model.The maximum VM stress value with vertical force: Model D>Model E>Model C>Model B>Model A;the maximum VM stress value with horizontal force: Model C>Model D>Model E>Model B>Model A;the maximum VM stress value with 45 °force : Model E>Model D>Model C>Model B>Model A;the maximum VM stress value with the largest bite force: Model D>Model E>Model A>Model B>Model C.3.A finite element analysis of endodontic treated mandibular first molar with contracted endodontic cavity restored in direct and indirect method: four finite element models were established.Model A: model with contracted endodontic cavity restored with bulk resin;Model B: model with contracted endodontic cavity filled with resin and then restored with all-ceramic crown;Model C: model with traditional endodontic cavity restored with bulk resin;Model D: model with traditional endodontic cavity filled with resin and then restored with all-ceramic crown.The maximum VM stress value with vertical force:A and B are nearly equivalent,Model C<Model D;the maximum VM stress value with horizontal force: Model A>Model B,Model C>Model D;the maximum VM stress value with 45 °force : Model A<Model B,Model C>Model D;the maximum VM stress value with the largest bite force: Model A<Model B,Model C>Model D.Conclusion1.Whether it is a natural tooth or endodontically treated tooth,PCD is the stress concentration area of the tooth,and the preservation of PCD can better transfer the stress to the root.2.The preservation of PCD alone may not improve the resistance to tooth fracture,but in this way,the tooth fracture may be prone to restore again which contribute to the longterm retention of teeth.3.The stress distribution of teeth with GECs is most similar to that of natural tooth.5.Compared with traditional and truss endodontic cavity accesses,CECs and GECs can significantly increase the resistance to tooth fracture.But more experiments are needed to confirm if contracted endodontic cavity access take greater advantage of that compared with computer-aided design–based guided endodontic cavities.5.With CEC and directly restored by resin,the resistance to tooth fracture can be improved.However,when restored with the all-ceramic crown,compared with the traditional endodontic cavity,the contracted endodontic cavity cannot increase the resistance.