Study On Application Of Protaper Next Ni-Ti Rotary System In Root Canal Retreatment

Root canal therapy is an effective method for the pulpal and periapical disease.In recent years,with the development of materials and the technologies,the success rate of root canal therapy has been improved.However,due to the complexity of the anatomy of the root canal system,the limitations of endodontic instruments,and some iatrogenic errors,there are still some cases in failure.Studies have shown that the Persistent infection or Secondary infection is the main cause of root canal treatment failure.Non-surgical root canal retreatment can further eliminate the infection and promote the healing of periapical lesions,which is the preferred treatment method after root canal treatment fails.In the non-surgical root canal retreatment,removing the root canal filling material thoroughly is not only a prerequisite for further removal of the infection source,but also a key step to affect the success of the root canal retreatment.At present,various methods have been used to remove the filling materials.Among them,the machine nickel-titanium instruments have the most extensive clinical applications because of their high removal efficiency,good shaping ability,and easy operation.ProTaper Next was released in 2013.It is made of a special M-wire nickel-titanium alloy and features a rectangular cross-sectional design and an asymmetric rotation.The unique design provides a larger space for debris exclusion and significantly improved preparation and cleaning efficiency.Studies have shown that the ProTaper Next can effectively remove the filling material in the curved root canal,but its application effect in removing the oval root canal is not yet clear.In this study,single mandibular premolars were selected as subjects to compare the effectiveness of the ProTaper Next instrument system with the traditional ProTaper Universal retreatment system and the hand files in root canal retreatment.The residual filling materials and the amount of apically extruded debris were evaluated for the retreatment performance of ProTaper Next,and the effects of the resin-based sealer AH Plus and the bioceramic sealer iRoot SP on the removal effect of the root paste by ProTaper Next were compared.The auxiliary ultrasonic and the XP-endo Finisher rinse promote the cleaning effect of ProTaper Next retreatment.The study aims to provide clinicians with a reference for the selection of appropriate instruments and methods.The study is divided into the following three parts:1.Efficacy of ProTaper Next NiTi systems in removing root canal filling material during root canal retreatmentMETHODS: A total 60 mandibular premolars were instrumented up to F2 with ProTaper Universal,The specimens were randomly divided into 6 groups and filled with continuous wave of condensation technique.,Groups 1,3,5 were filled with gutta-percha and AH Plus and groups 2,4,6 were filled with gutta-percha and iRoot SP.After storage for 4 weeks at 37°C in a 100% humidity environment,the retreatment was carried out in groups 1 and 2 with H files,groups 3 and 4 with ProTaper Universal retreatment(PTUR)and groups 5 and 6 with ProTaper Next(PTN).All groups are prepared up to #40.The working time was calculated.After preparation,the specimens were split longitudinally and evaluated by stereomicroscope.The photographs were captured and analyzed using AutoCAD software.Then statistical analyses were performed.RESULTS: The operation time of PTN and PTUR group was significantly less than that of H group(P<0.001),but there was no statistical difference between PTN group and PTUR group(P>0.05).There was no significant difference in the amount of fillings in each group(P>0.05);The two kinds of sealers had no significant influence on the operation time and the residue of the filling(P>0.05).2.Evaluation of apically extruded debris during root canal retreatment with ProTaper NextMethods: The collection of tooth,root canal preparation,root canal obturation and experimental grouping were completely consistent with the experiment 1.During the retreatment,2 mL NaOCl after each instrument changed and a total of 12 mL for irrigation.Apically extruded debris were collect by 1.5% agar gel model during retreatment,Comparative analysis of the amount of apically extruded debris(10-5 g)for each groups and subjected to statistical analysis.Results: There was a statistically significant difference(P<0.001)in the amount of apically extruded debris from each group,with the leas in PTN group,followed by PTUR group,and the most in the H files group(P<0.05).Two kinds of sealers had no significant effect on the amount of apically extruded debris(P>0.05).3.The effects of XP-Endo Finisher on retreatment with ProTaper NextMethods: Thirty mandibular premolars were prepared up to F2 by ProTaper Universal,and filled with continuous wave vertical compression method with gutta-percha and AH Plus sealer,teeth were stored at 37°C,100% humidity environment for 4 weeks.Samples were randomly divided into 3 groups(n=10).Removal of the root canal filling was performed using PTN rotary files and conventional rinse with NaOCl for 60 s in the control group,the PTN and a Supplementary Step with XP-endo finisher instruments or ultrasonic in other groups respectively.After retreatment,the samples were sectioned longitudinally and evaluated by SEM.The scores of debris and smear layer at the coronal,middle,and apical regions were comparative analysisResults: The ultrasonic group and XP-endo Finisher group revealed significantly lower scores of debris and smear layer than control group at the coronal,middle,and apical regions(P<0.05).There was no significant difference between ultrasonic group and XP-endo Finisher group(P> 0.05).Conclusion:1,ProTaper Next nickel-titanium preparation system can safely and effectively remove the root canal filling,but there is still a certain amount of residue.2.ProTaper Next produced less apically extruded debris than ProTaper Universal retreatment files and H files during root canal retreatment.3.XP-Endo Finisher Significantly improved the removal of debris and smear layer,and get cleaner root canal wall in the endodontic retreatment.