| Objective:Root canal therapy is widely used in the treatment of endodontic and periapical diseases because of its ability to retain the natural tooth tissue in the oral cavity,the process of RCT includes root canal preparation,root canal disinfection and root canal filling.The modern concept of root canal preparation including cleaning and shaping of the root canal,to completely remove the infected material and dentin of root canal,and shap the irregular root canal to be continuous inverted cone with wide coronal and small tip,keep the original canal the direction basically.The shape change of maintenance is a prerequisite for improving the disinfection and filling of root canal.Root canal system is the complex pathway of the soft tissue,there is a certain degree of curvature in most of the root canals,especially the roots of molar canal.In the process of RCT,there is a higher risk in the curved root canal to be root canal deviation,elbow or step formation during root preparation.The difficulty of RCT by oral doctors increased,mean while,it is one of the important reasons of the failure of RCT.In recent years,nickel-titanium root canal preparation instruments become more and more popular in the curing of endodontic diseases because of thebetter flexibility and excellent cutting ability than traditional root canal instruments.Many studies show that nickel-titanium instruments have a better shaping and cleaning ability than the traditional stainless steel equipment but cause more dentin microcrackin curved root canal as well.It’s seen that the crack maybe a potential risk of vertical fracture of the root.It will greatly reduce the long-term effect of RCT.Cone-beam CT has been widely used in clinical diagnosis and treatment of oral disease,it through the three-dimensional scanning and digital processing of a particular region,in a noninvasive manner will scan bone tissue,area of dental hard tissue and surrounding anatomical structures related to digital display three-dimensional image,intuitive and accurately reflects the lesion location,number,size and extent of damages.In recent years,the TFA root canal preparation system and the S3 root canal preparation system have been proved to have better preparation effect than the traditional instruments in smaller bending anterior teeth and premolars.With the help of CBCT and microscope,this experiment makes a comparison of 4 different root canal instruments(K-file,ProTaper Universal,TFA,S3)in preparation of curved root canal in deviation degree and the number of dentin microcrack,in order toprovide theoretical basis for clinic dentist in selecting root canal preparation instruments better.Methods :1.According to the inclusion criteria,50 cases of mandibular first molars were extracted by 2015.6 to 2016.6 for periodontal disease,and were randomly divided into 5 groups: blank control group,K-files group,ProTaper Universal group,TFA group and S3 group.,After the opening of pulp crowns mark fixed reference point by 16 mm working length of crown truncation,epoxy resin embedding root to the cemento enamel junction boundaries,lined with hydrophilic silicone impression materials to simulate the alveolar bone and periodontal ligament,in the experimental process all the teeth were stored in deionized water beside the operations.2.Root canal preparation was performed in all theteeth sample except the blank control group,and CBCT scan was performed before and after the preparation.The scanning images were analyzed by CBCT software.The root canal dentin of proximal and distal root canal was calculated before and after root canal preparation,then the root canal deviation was analyzed by the theoretical formula proposed by GamBill.3.All the samples in 5 groups make horizontal grinding,each section under stereomicroscope magnification of 20 observation,according to whether there are any dentin defect record results,differences were analyzed between dentin microcrack.Results :1.In the vitro teeth samples of K-file group,ProTaper Universal group,TFA group and S3 group,the average root canal deviation in the 2mm distance from the apical were 0.204 mm,0.182 mm,0.094 mm and 0.156 mm,the comparisons between each two groups showed that there was significant difference between TFA group and ProTaper Universal group(P < 0.05),but there was no significant difference between other groups(P > 0.05).2.In the vitro teeth samples of K-file group,ProTaper Universal group,TFA group and S3 group,the average root canal deviation in the 5mm distance from apical were 0.579 mm,0.489 mm,0.292 mm and 0.334 mm.The comparisons between each two groups found that the differences were significant when TFA group was compaired with K-file group and ProTaper Universal group,meanwhile,the difference was significant whenS3 group was compaired with K-file group and ProTaper Universal group(P < 0.05).The differences between K-file group and ProTaper Universal group,TFA group and S3 group were not statisticalsignificant(P > 0.05);3.In the vitro teeth samples of K-file group,ProTaper Universal group,TFA group and S3 group,the average root canal deviation in the 8mm distance from apical were 0.241 mm,0.225 mm,0.206 mm,0.172 mm.The comparison between each two of them found that the differences were no statistically significant(P > 0.05).4.Dental root canal microcrack appears after preparation: the blank control group and K-file group had no microcrack.In ProTaper Universal group,there are 4 microcracksin the 2mm distance from apical,3 microcracksin the 5mm distance from apical and 2 microcracksin the 8mm distance from apical.In TFA group,there are 2 microcracksin the 2mm distance from apical,2 microcracksin the 5mm distance from apical and 1 microcrackin the 8mm distance from apical.In S3 group,there are 2 microcracksin the 2mm distance from apical,3 microcracksin the 5mm distance from apical and 1 microcrackin the 8mm distance from apical.Statistical analysis showed that there was no statistical difference between the groups(P > 0.05).Conclusion:1.In my study,four kinds of root canal preparation filesmake different degrees of root canal deviation,and the largest deviation was appeared in the middle 1/3 of the root canal.2.TFA nickel-titanium root canal file has better uniform cutting on the root canal wall and showed a better central positioning ability in the apical area of root canal(2mm distance of from apical).3.The central positioning ability of TFA and S3 nickel-titanium root canal files in the middle area of root canal(5mm distance of from apical)were better than K-file and ProTaper Universal files4.The central positioning abilities of the crown area(8mm distance of from apical)didn’t show significant difference in 4 kinds of root canal preparation files.5.There was no microcrack founds in root dentin after root canal preparation with K-file.6.ProTaper Universal,TFA,S3 nickel-titanium root canal files make microcracks in the root canal preparations,and the closer to the apical the more dentinal microcracks appeared with the preparation of ProTaper Universal. |
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