الفهرس 
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Abstract
The aim of this study was to evaluate the effect of different irrigation protocols on the push-out bond strength of EndoREZ root canal obturation system to root canal dentin and to determine the mode of bond failure that have occurred after dislodgment of the filling material.
A total of 60 human permanent single rooted teeth were used in this study. Teeth were decoronated, cleaned and shaped using step-back technique.
Samples were divided into six groups (10 each) according to the final rinse used: group I, root canals were finally irrigated by 5ml 2.5%NaOCl for 1 minute, followed by rinsing with 5ml distilled water for 1 minute. Group II, root canals were finally irrigated by 5ml 17% EDTA for 1 minute, followed by rinsing with 5ml distilled water for 1 minute. Group III, root canals were finally irrigated by 5ml 17% EDTA for 1 minute, followed by 5ml 2% CHX for 2 minutes. Group IV, root canals were finally irrigated by 5ml Biopure MTAD according to the manufacturer’s instructions: 1ml of Biopure MTAD was placed in the canal for 5 minutes, followed by rinsing the canal with 4ml of MTAD. Group V, root canals were finally irrigated by 5ml Biopure MTAD with the same manner as in group IV, followed by 5ml 2% CHX for 2 minutes. Group VI, root canals were finally irrigated by 5ml 2% CHX for 2 minutes. EndoREZ root canal obturation system was used for obturating all samples using cold lateral compaction technique.
The bond strength of the tested sealer was measured by the push-out test, and the mode of bond failure was determined under a scanning electron microscope.
The results of the push-out test showed that group V (MTAD/CHX) yielded significantly the highest mean push-out bond strength especially at the coronal segment. There was no statistically significant difference between the rest of the groups (NaOCl, EDTA, EDTA + CHX, MTAD and CHX) which showed the statistically significantly lowest means push-out bond strength. The apical and middle bond strength in group I (NaOCl), were significantly higher than the coronal bond strength. In group VI (CHX), the bond strength at the apical segment was significantly higher than the middle and coronal bond strength.
The results of mode of failure examination revealed that all samples in group I (NaOCl), exhibited only mixed types of failures. Group II (EDTA), showed the predominance of the adhesive failure (80%), while only 20% of the samples exhibited mixed failures. Group III (EDTA + CHX), showed predominantly adhesive failures (70%), whereas mixed failures were detected in 30% of the specimens. Group IV (MTAD), showed that 70% of the specimens exhibited mixed type of failures, and adhesive failures were detected in 30% of samples. Group V (MTAD + CHX), showed that 80% of the examined specimens were predominantly mixed failures, whereas adhesive failures were detected in only 20% of the specimens. Group VI (CHX), showed that 70% of the samples exhibited mixed modes of failure, while 30% of the samples showed adhesive failures.
Based on the results obtained from this study it can be concluded that:
1) The bond strength of EndoREZ to dentin was affected by the type of final rinse.
2) The use of a final rinse of CHX after MTAD significantly improved the adhesion of EndoREZ to dentin especially in the coronal segment.
3) There was no effect on bond strength when using NaOCl, EDTA, EDTA/CHX, MTAD, or CHX as a final rinse.
4) The use of NaOCl or CHX as a final rinse resulted in greater bond strength at the apical region than that at the coronal region.
5) Cohesive mode of failure was completely absent in the six groups.
6) NaOCl group showed only mixed mode of failure.
7) Adhesive mode of failure predominated in EDTA group and EDTA+CHX group.
8) Mixed mode of failure predominated in MTAD group, MTAD+CHX group and in CHX group.