The Effect Of Dentin Loss And Dentinal Microcrack Caused By Canal Instrumentation Wtih Large Taper Instruments On Biomechnical Status Of Tooth

Tooth fracture was regarded as the third reason for tooth loss following caries and periodontosis.Tooth loss lowers life quality score.Thus,tooth fracture has drawn wide attention.Many patients faced tooth loss may choose prosthodontic treatment.However,restorations mostly had limitations,such as low masticatory efficiency,high priced,numerous following maintenance.These restorations had serious disadvantage.Therefor,it made sense to conserve natural tooth.It was known that tooth fracture rate manifies for tooth after endodontic therapy.And root canal treatment was the most popular way to cure pulposis and periapical disease at present.Canal preparation was an essential step in endodontic treatment and directly connected with the effect of root canal therapy.With the wide use of nickel titanium canal instruments,dentin loss in the course of canal enlargement.Besides,root canal treatment could also resulted in dentinal microcrack.These factors may affect resistance of tooth and induce endodontically treated tooth to fracture.Objective This experiment aims to study stress status of maxillary second premolar under condition of dentin loss in the procession of root canal enlargement and microcrack formation.This may provide explanation for higher incidence of root fracture of endodontically treated teeth.Microcracks of different configuration probably have various effect on stress of dentin.And this finding may make contributions to the evaluation of canal enlargement instruments.Methods Twelve maxillary second premolars were selected for this experiment.Tomographic images of intact teeth and teeth after instrumentation could be gained by Micro-CT scanning.Data were acquired for establishment of three dimensional finite element models with finite element software.The models were imported into 3-Matic STL to calculate volume of intact dentin,intact canal and canal after canal enlargement.Thus,the percentage of dentin loss in the processing of root canal preparation of intact dentin was obtained.Then it was studied that the stress status of twelve 3D models under buccal and lateral force loading.It was analyzed the maximum principal stress distribution of dentin prior to and after canal instrumentation.And the representative model both in stress size and stress distribution were selected.Microcracks of different morphology were established according to the direction,length,depth and location.Finite element models were established after the boolean calculation between above representative model and different microcracks.This models with microcracks were divided into groups according to their depth,length and location.All the models were loaded with buccal and lateral force.It was studied that the effect of microcracks on dentin and various effects of different microcracks by means of analyzing stress value and distribution of all the models with microcracks.Results When buccal force was applied on tooth,maximum principal stress was mainly focused on cervical area of lingual surface of dentin.When lateral force was loaded,maximum principal stress distributed at coronal part of the opposite side of force loading.Stress magnitude had little difference prior to and after canal instrumentation.Mean dentin loss volume in the processing of root canal preparation was 3.7955mm3.The percentage of dentin loss during canal enlargement of dentin tissue was 1.88%.When microcracks were generated,peak value of dentin stress magnifies a lot in condition of buccal or lateral force was applied.Some of stress concentrated area tranferred to the location of dentinal microcracks.The amplification of dentin stress and the transfer of stress concentrated area were both linked to the morphology of microcracks.Conclusion The percentage of dentin loss during canal enlargement of dentin tissue was minor.And this may play a significant role in unconspicuous change of dentin stress prior to and after canal instrumentation.The maximum stress magnitude magnifies and stress distribution varies for tooth with dentinal microcracks when teeth were loaded with buccal and lateral force.And microcracks of unlike configuration cause various results.This may play an important role in root fracture of endodontically treated teeth.