Effect Of Different Concentrations And Different Rinsing Time Of EDTA On The Root Canal Wall And Fracture Resistance Of Roots

Objective:The root canals were rinsed with different concentrations of EDTA and different times. A part of them were selected to observe the effect of smear layer removal and erosion by scanning electron microscope. The other samples were filled with AH-plus, and then measure the fracture resistance of roots.The purpose of this study was to measure the effect of different concentration of EDTA and different rinsing time on smear layer removal and erosion and fracture resistance of roots, meanwhile, provide laboratory evidence for further clinical therapy to reduce the incidence of vertical root fracture, increasing the success rate.Methods:200single canal premolars were cut at13mm from the root apex. Adjusted the fixed reference points when the tip of the K-type just emerged from the root hole, the working length of which is lmm lesser than the distance from equipment stopper piece to tip. They were instrumented to F3with handed Protaper system. After changed equipment, rinsed root canal firstly with2ml1%NaClO for1min, and then2ml saline, finally the5%or17%EDTA were chose with5washing times. After that, rinsed root canals with10ml1%NaC10for1min and5ml saline for secondary rinse. Randomly selected10samples from each group. Drilled a ditch about2mm in the buccal and lingual side of the in vitro root respectively. After broken the root and exposed root canal wall, turned into70%,80%,90%ethanol and anhydrous ethanol to dehydrate step by step and then sprayed gold. Under nanosem430thermal field emission SEM, magnified the view1000times to observe smear layer removal and erosion conditions. The other10samples of each group were filled with AH-plus.1week later, the samples were packaged in PVC tube which were filled with superhard gesso exposing. Placed all samples in the universal testing machine, loaded each specimen until the toot fractured. Recorded the maximum load of the specimens when the root fractured. The statistical analysis was processed using SPSS17.0.For different concentrations of EDTA on different time in different parts, Kruskal-Wallis test and Mann-Whitney U test were used. Flexural strength of the root canal was analyzed by one-way analysis of variance(ANOVA), factorial analysis and SNK test. The level of significance was0.05. Results:1. The effect of smear layer removal:In group A, there was no difference between A1and A2, A4and A5, in contrast, there was significant difference between A2and A3, A3and A4.In group B, only the difference between B1and B2as well as B2and B3reached statistical significance.2. Erosion:No difference was seen among different subgroups of group A. However, only the difference between B4and B5did not reach significance.3. The fracture resistance of roots:In group A, there was no significant difference between A1and A2, but other groups showed significant difference. In group B, there was no significant difference between B1and B2, but the difference reached statistical significance when others were compared in pairs.Conclusion:1. Our results show that the longer time with5%EDTA, the more obvious the effect of smear layer removal. Corrosion occurs when flushing time exceeds10min, but there was no difference. Flexural strength gradually increased with extension of time, which peaked at10min and then decreased.2. The effect of rinsing root canal wall with17%EDTA for1min was better than that for40s. when more than1min, as the extension of time, the effect of smear layer removal was not obvious different, meanwhile, the root canal wall corrosion phenomena occurs. Considering the resistance to fracture peaks at1min, it aslo reduces reasonably.3.The effect of smear layer removal and the fracture resistance of root with5%EDTA rinsing for10min were better than that with17%EDTA for1min.Rinsing at low concentration for a long time worked as well as at high concentrations.However,10min was not suggested in clinical practice because of its long duration.The effect of smear layer removal with5%EDTA for5min was similar to that with17%EDTA for1min,moreover,the degree of erosion was low,although the fracture resistance of root with5%EDTA rinsing for5min was inferior than that with17%EDTA for1min.Therefore,rinsing with5%EDTA for5min may be a better method in clinical therapy.