Biomechanical Properties Of Premolar And Molars With Different Endodontic Cavities:A Finite Element Analysis

ObjectiveSuccessful root canal treatment depends on the adequate debridement and filling of the entire root canal system.For this purpose,in the clinical context,dentists usually prepare a much larger endodontic cavity to detect and clear the root canal.However,removal of much of the tooth structure can undermine its resistance to fracture under functional loads.Traditional endodontic cavities(TEC)involve straight-line pathways into the canals to enhance the efficacy of instrumentation and prevent procedural errors.The consequent removal of the tooth structure,coronal to the pulp chamber,along the chamber walls and around the canal orifices,is the most frequent cause of fracture in endodontically treated teeth,because the removal of a large amount of dental tissue can threaten the integrity of the dental structure,facilitating fracture.Therefore,it is extremely important to determine how to protect the first maxillary molar and avoid destroying much dental tissue during endodontic treatment.Minimally invasive endodontics(MIE)aims to improve the traditional endodontic treatment by designing precise access cavities and pulp chamber finishing.Protecting the cingulum,the oblique ridge,and the pulp chamber roof,which play very important roles in the chewing function,can enhance the tooth fracture strength.Minimally invasive endodontics cavities(MEC)have recently been designed to minimize the removal of the tooth structure.Some dentists have used this contracted access cavity design during clinical endodontic treatments.In previous in vitro studies,several authors have found that compared with TEC,MEC improved the fracture strength under a continuous load.However,other studies have shown no obvious difference between MEC and TEC in maintaining fracture strength.The aim of this study was to compare the biomechanical properties of premolar and molar containing different endodontic cavities using the finite element method(FEM).Materials and Methods1.An intact,noncarious,mature first human maxillary premolar was obtained and scanned with Skyscan 1072 high-resolution micro-CT(Skyscan,Aartselaar,Belgium),with a voxel dimension of 20 ?m.An interactive medical image control system(MIMICS 16.0,Materialise,Leuven,Belgium)was used to identify the different hard tissues visible.The files were refined with reverse engineering software(Geomagic Studio 10,Geomagic,Inc.,Research Triangle Park,NC).The software SolidWorks(Dassault Systems S.A.,Concord,MA,USA)combined the enamel and dentin.The endodontic access cavities were then designed on the solid model with SolidWorks:one designed with TEC and other five designed with MEC.An intact tooth(IT)model was used for comparison.The models were cross-linked to 3D FEM models with the software ANSYS14.5(ANSYS,Inc.,Canonsburg,PA,USA).In the endodontic treatment models(MEC,TEC,and EEC models),the roots were filled with gutta percha.The area extending from 2 mm beneath the canal entrance to the level of the pulp horn was filled with flowable composite resin,and the cavity was restored with composite resin.The cement layer was 0.04 mm thick.Each model was subjected to three different force loads directed at the occlusal surface.The stress distribution patterns and the maximum von Mises(VM)stresses were calculated and compared.2.Three finite element analysis models of a maxillary first molar were built like Experiment one.The endodontic access cavities were then designed on the solid model with SolidWorks: a traditional endodontic cavity(TEC),a minimally invasive cavity(MEC),and an extended endodontic cavity(EEC).Each model was subjected to three different force loads directed at the occlusal surface.There was a vertical force load and two different oblique force loads.The stress distribution patterns and the maximum von Mises stresses were calculated and compared.3.Three finite element analysis models of a mandible first molar were built like Experiment one.The endodontic access cavities were then designed on the solid model with SolidWorks: one designed with TEC and other three designed with MEC.An intact tooth(IT)model was used for comparison.Each model was subjected to two different force loads directed at the occlusal surface.There was a vertical force load and a oblique force loads.The stress distribution patterns and the maximum von Mises stresses were calculated and compared.Results1.For the maxillary first premolar,the peak von Mises stress on all models was at the site of the force load.The occlusal stresses were spread in an approximate actinomorphic pattern from the force loading point,and the stress was much higher when the force load was close to the access cavity margin.Whether on the corona,cervical or apex,the peak VM stresses in the CEC models with one access cavity located at the lingual bevel of buccal cusp were lower than in the TEC model.While no obvious advantages in stress distribution could be founded on the other CEC models compared with on the TEC model,especially under the lateral force loads.2.For the maxillary first molar,the peak VM stress on all models was at the site of the force load.The occlusal stresses were spread in an approximate actinomorphic pattern from the force loading point,and the stress was much higher when the force load was close to the access cavity margin.The peak root VM stresses on the rootfilled teeth occurred at the apex and were significantly higher than that on the intact tooth,which appeared on the pericervical dentin.The area of pericervical dentin experiencing high VM stress increased as the cavities extended and the stress became concentrated in the area between the filling materials and the dentin.3.For the mandibular first molar,the von Mises stress distribution tendency on occlusal of all models were similar to the experiment one and experiment two.On the occlusal,the peak von Mises stress on TEC model were higher than the stress on MEC models.On the cemento-enamel junction(CEJ),the maximal stress on MEC 3 model was higher than the stress on other models,and no obvious difference were found in the stress distribution between TEC,MEC 1 and MEC 2 model.On the apex,the stress on MEC 2 model were lower than other models,and the stress distribution on TEC was similar to MEC 1 and MEC 3 model.Conclusion1.For the maxillary first premolar,five minimally invasive cavities were prepared on the maxillary premolar while only one which prepared with one access cavity that appeared on the lingual bevel of buccal cusp could reduce the stress concentration compared with the TEC model.2.For the maxillary first molar,the stress on a tooth is more concentrated when the distance between the margin of the access cavity and the force loading area is small.With enlargement of the access cavity,the stress on the pericervical dentin increases dramatically.3.For the mandibular first molar,the stress distribution on CEJ and apex of MEC 2 model were lower than other MEC models and TEC model.