الفهرس 
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Abstract
The aim of the study was to evaluate the concept of using a recently introduced NiTi rotary instrument that is manufactured from M-Wire alloy and specifically designed for cleaning and shaping of the canals in comparison to regular files retreatment technique where the parameters to be evaluated were the amount of residual filling material on the root canal dentin and the time required for retreatment.
master apical file was inserted in the canal, the root was ground from the buccal aspect with carborundum disc until the file appears along the whole length of the canal so longitudinal section of the canal was obtained.
Total time records were evaluated until the complete removal of gutta percha. In all-time records of the time taken for handling of instruments, changing of files, irrigation, etc. was excluded.
A total of eighty human permanent mandibular molars were used in this study. Access cavities were done and special measure were taken to ensure standardization and reproducibility of samples.
The samples were divided into two groups according to the type of sealer used during obturation. group I (n=40) where AH Plus sealer was used during obturaion and group II (n=40) where Tubliseal sealer was used during obtration. Then each group was divided into A and B subgroups where in A subgroups Protaper Next files were used in mesiobuccal canals retreatment and in B subgroups Protaper Retreatment kit were used in mesiobuccal canals retreatment.
Amount of remaining gutta percha assessment:
The roots were then scanned using stereomicroscope at a fixed magnification of x20 to analyze the amount of remaining filling material in each group at coronal, middle and apical thirds. Images were captured using a digital camera fitted on the microscope, and then transferred to desktop and saved as JPEG format. ImageJ Software was used to analyze the obtained images. No attempt was made to distinguish between residual filling material and sealer.
Time required for retreatment assessment:
The time required for removal of root canal filling material from starting the first instrument until the completion of the re-instrumentation was recorded as (T).
Results:
Concerning the amount of remaining gutta percha:
No major differences in results between PTN files and Protaper Retreatment kits except in the middle third results of the AH Plus group, where Protaper Retreatment kit results showed less remnants of gutta percha than that of Protaper Next file . Both coronal and middle thirds showed less reminants than the apical third. Moreover, more remanants were observed in the middle and apical thirds of the Protaper Next subgroup when using AH plus sealer compared to that when using Tubliseal.
Concerning the time required for retreatment:
The Protaper retreatment file system showed less time required for retreatment than the Protaper Next files in the two different sealer groups. No difference in retreatment time regarding the type of sealer used either AH plus sealer or Tubliseal .
Conclusion:
1. No retreatment system was efficient to completely remove root canal filling.
2. The root canal filling in apical one third was inefficiently removed by both systems in comparison to the middle and coronal thirds.
3. At both Coronal and Apical thirds of the root canal; Protaper Retreatment and Protaper Next were comparable to each other in removal of root canal filling disregarding the type of sealer used.
4. At the Middle third ; Protaper Retreatment was able to efficiently remove root canal filling specifically using AH plus root canal sealer.
5. The Protaper Retreatment files takes less time in retreatment procedures than the Protaper Next files.
6. X1 file of Protaper Next files has a high incidence to fracture when used in retreatment cases.
Recommendations:
1. Further studies can be employed to assess the performance of the PTN files in retreatment such as transportation, post operative pain and debris extrusion.
2. Further researches to be employed to assess the use of adjunctive aids as solvents with PTN for more efficient removal of gutta percha in retreatment procedures & to concern different root canal curvatures.
3. Further studies can be employed to use larger files in PTN files as X3 and neglecting the use of X1 file.