الفهرس 
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Abstract
Summary and conclusions
The efficient shaping of the root canals and maintaining their curvatures is an essential goal for every root canal treatment. However, an accurate prediction of the performance of endodontic files in the curved canals is not always achievable.
The introduction of the new single file techniques is promising in providing efficient, safe and quick preparation with less time consuming and more comfortable to the patient, where minimizing the number of files used inside the root canals aims to reduce the procedural errors associated with these large sequences of files. However, how these new files behave inside the root canals usually requires thorough investigations.
The aim of this study was to compare and evaluate the efficacy of different single file techniques in terms of shaping ability of the canal according to canal centering, canal transportation, change in canal volume, change in canal angle and radius of curvature, apical extrusion of debris after preparation with the four single-file systems, also the preparation time was recorded. The incidence and the intensity of post-operative in patients treated with these files was examined as well.
The study was divided into two parts; the first part was carried on natural mandibular molar teeth (in vitro), while the second part
was carried on endodontic patients with symptomatic irreversible pulpitis. In the first part; 80 canals of the mesial root of mandibular molars were included in the study. After cleaning the teeth from any deposits, access cavity preparations were prepared. The teeth were scanned using Micro-CT before canal preparation. The canals were then dived into four groups according to the single-file system used; WaveOne Gold files, RECIPROC Blue files, HyFlex EDM files and One Shape files. Each file prepared four canals then the file was discarded. Saline was used as irrigating solution. The teeth were placed in special glass vials for the collection of the extruded debris apically that were weighted before and after preparation to record the quantity of extruded debris. The time taken by each file type to reach the full working length was recorded. The teeth were the scanned again with Micro-CT for the post-instrumentation records. The data from the pre- and post-instrumentation scans were recorded, tabulated, compared and statistically analyzed using one‑way analysis of variance (ANOVA) with the level of significance set at
= 0.05.
In part of the study, after calculation of the sample size, 80 patients that the inclusion criteria participated in the study. after canal preparation with the four different single-file systems, the patients were instructed to record the incidence and the intensity of
post-operative in different time intervals; 6h, 12h, 24h, 48h, 72h after canal preparation. The patients received two different scoring systems in a single paper to record the pain scores. The data from the patients scores were tabulated and statistically analyzed using one‑way analysis of variance (ANOVA) with the level of significance set at = 0.05.
In the in vitro part of the study, the results of canal centering ratio and canal transportation showed that no significant difference was found among the four file groups at the middle and the coronal level. However, a significant difference was found at the apical level (P < .05), where WaveOne Gold showed the best centering ratio and the least amount of canal transportation. The change in canal volume was significant at the coronal level (P < .05) where the change in canal volume was higher for the HyFlex EDM group than the other groups, no significant difference was found between the other groups at the apical level, middle level or in the total percentage of canal volume. No significant difference in change of canal angle of curvature or radius of curvature after canal preparation with the four tested groups
The results of apical extrusion of debris showed that WaveOne Gold files extruded the least quantity of debris. While
HyFlex EDM files showed the highest amount of apically extruded debris.
No significant differences in canal shaping time were detected among the four groups.
In the in vivo part of the study, the results showed that patients suffered from pre-operative pain showed different scores of the post- operative pain. In all the four groups the post-operative pain scores were lower than the pre-operative scores and then decreased gradually during the time of pain scores recording by the patients. No significant difference in the incidence or intensity of post- operative pain was found after canals preparation with the four groups.
from the results of the current work, it could be concluded that:
➢ File design had a significant influence on the levels of the root canals regarding canal centering, transportation and change in canal volume.
➢ The file design or the motion kinematics had no effect on the change in canal curvature or the shaping time.
➢ The quantity of apical extrusion of debris was affected by the file design and not the type of motion used.
➢ The incidence and intensity of post-operative pain were comparable with all groups.
Recommendations:
▪ Scanning with higher resolution imaging techniques such as nano-CT may be useful to accurately reflect the performance of the endodontic instruments inside the root canal system.
▪ The inclusion of different file systems with larger sample size may be desired to detect the influence of different file characteristics on the shaping performance inside the canals.
▪ Evaluation of the shaping ability of different file systems after root canal preparation in patients using Optical Coherence Tomography (OCT) is a prerequisite to detect the influence of oral cavity conditions on the behavior of these files.