الفهرس 
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Abstract
This study compared the efficacy of two retreatment systems (D-race, Neolix) in removal of root canal filling and effect on the pushout bond strength after reobturation.
Sixty extracted human single rooted teeth were decoronated, cleaned with NaOCl, shaped with protaper system and finally EDTA 17% then obturated using lateral compaction technique. Teeth were randomly divided into two groups according to retreatment system used. Half of the teeth were sectioned and investigated under the Scanning Electron Microscope after removal of gutta-percha and were not be refilled. The remaining specimens were reobturated with Total fill bioceramic sealer and tested by pushout bond strength test.
Data were analyzed by one- and two-way analysis of variance (ANOVA) was followed by Tukey’s HSD multiple comparisons tests to compare between sub-groups. Independent samples t-test were also performed.
D-race system showed lower statistically significant remaining root canal filling material than Neolix system in both coronal and apical thirds (p<0.05), however, it was non-significant in middle third.
The teeth reobturated with Totalfill bioceramic sealer after retreatment using D-race system showed higher statistically significant pushout bond strength than using Neolix system in coronal third (p<0.05), however, it was non-significant in middle and apical thirds.