الفهرس 
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Abstract
he aim of this study was to evaluate the push-out bond strength of EndoRez sealer and AH Plus sealer with dentin (whether sealers were used alone to fill the root canals without gutta-percha (thick sealer layer) or were used with gutta-percha, as obturation system (thin sealer layer), this study also aimed to examine the effect of thickness on bond strength of each sealer with dentin and also to compare voids percent between the two obturation systems (EndoRez and AH Plus obturation systems).
A total of fifty human single rooted teeth were used in this study. Teeth were decoronated, cleaned and shaped using crown down technique and irrigation protocol of teeth was done as follow:5ml 2.6%NaOCl,followed by 5ml 17% EDTA for 60 seconds and finally 5ml distilled water before using paper points to drying canals .Samples were divided into two groups and each group was divided into two subgroups:
Group (I): 20 teeth obturated using root canal sealers only
Group (II): 30 teeth obturated using root canal sealers with gutta-percha using lateral compaction technique
Group (I): formed of two subgroups
Subgroup (A): 10 teeth were obturated using EndoRez sealer only (without gutta-percha) and subjected to push–out test to evaluate the mode of failure.
Subgroup (B): 10 teeth were obturated with AH Plus sealer only (without gutta-percha) and subjected to push-out test to evaluate mode of failure.
Each tooth in group1 was divided into coronal and middle root thirds.
Group (II): formed of two subgroups
Subgroup (A): 15 teeth were obturated using EndoRez obturation system by lateral compaction technique.
Subgroup (B):15 teeth were obturated using AH Plus obturation system by lateral compaction technique.
Each tooth in group II was divided into coronal, middle and apical root thirds. Bond strength was evaluated using push-out test and the failure mode was analyzed using digital microscope (for the ten tested samples) and (additional five samples) of each obturation group were examined for voids by digital microscope.
Results of bond strength showed that EndoRez sealer had lower push-out bond strength than AH Plus sealer whether the sealer material was used alone inside the canal or used with gutta-percha (as obturation system). Bond strength of thick sealer (when root canal filled with sealer only) was higher than bond strength of thin sealer (when root canal filled with the same sealer and gutta-percha), and EndoRez obturation system showed higher voids percent than AH Plus obturation system.
Regarding the results of the mode of failure(for EndoRez compared with AH Plus obturation groups: mixed failures predominated in coronal ,middle and apical thirds for EndoRez obturation group and for AH Plus obturation group: adhesive failure predominated at coronal third, while mixed failure predominated at middle and apical third. On the other hand, for EndoRez compared with AH Plus sealer groups: adhesive failure predominated in the coronal and middle third for EndoRez sealer group and for AH Plus sealer group: the mode of failure equally distributed among adhesive, cohesive and mixed failures in the coronal third and there were mixed failures predominated in middle third.
Conclusion:
1-The epoxy resin-based sealer (AH Plus) had higher push-out bond strength than UDMA-based sealers (EndoRez) when used as sealer alone inside canal (without gutta-percha) or when used as obturation system (sealer with gutta-percha) using lateral compaction technique.
2-The bond strength when the root canal was filled with sealer alone (thick sealer layer) was higher than when the root canal was filled with sealer and gutta-percha as an obturation system (thin sealer layer).
3-EndoRez obturation system had higher voids percent value than AH Plus obtur