الفهرس 
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Abstract
This study compared the efficacy of Reciproc, WaveOne reciprocating systems and the ProTaper Universal retreatment system in removal of endodontic filling materials (gutta-percha and sealer) from moderately curved canals of mandibular molars. Analysis of the remaining filling material was done using cone beam computed tomography.
Thirty extracted mandibular first molars were selected, shaped with Revo-S rotary system up to SU file and then obturated by cold lateral compaction technique and resin based sealer. The samples were randomly divided into three experimental groups according to the system used for retreatment as follow:
group 1: Reciproc R25.
group 2: WaveOne primary file.
group 3: ProTaper Universal retreatment system.
The volume of gutta-percha was measured before and after retreatment by using cone beam computed tomography (CBCT).
After Data were collected and coded, they were subjected to statistical analysis using the SPSS IBM version 20 software.
The Kruskal-Wallis test was used while the Wilcoxon test was used to test for changes of median volume before and after intervention. The Friedman test was used for all groups to test for differences of volume % of filling material remaining between the coronal, middle and apical zones per group while the Kruskal-Wallis test was used to compare between groups at each zone.
According to these results there was no statistically significant difference between the volumes of filling material remaining between the three groups after retreatment. In comparison to each zone in the three groups there was only significant difference in the middle third (P<0.05) as Reciproc left highest volume of gutta-percha in middle zone in comparison with other groups.