الفهرس 
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Abstract
O
ur study was conducted to evaluate the efficiency of two rotary Ni-Ti retreatment systems which are ProTaper Universal retreatment and Endostar-RE. Retrievability and the time required for retreatment process. The total number of samples were 40 single canal canines divided into two groups of twenty canals according to retreatment system used.
In group (I) the teeth were obturated by TotalFill BC sealer while in group (II) the teeth were obturated by ADSEAL sealer. The groups were farther sub-grouped according to retreatment file system used in retreatment. In Sub-group A retreatment was done using ProTaper Universal Retreatment files while in subgroup B retreatment was done using Endostar-RE retreatment files.
Teeth were decoronated, instrumented using Mpro rotary system then the preparation completed with Mani k files up to size#50/0.02 and then obturated with gutta percha and sealers according to groups using cold lateral compaction technique. After obturation specimens were sealed with temporary filling and incubated in 100% humidity and 370 c to allow sealer to set.
After retreatment teeth were splitted longitudinally and imaged using digital microscope then analyzed by IMAGE J software to measure percentage of remaining root filling material in coronal, middle and apical third of root canal.
The time required for retreatment was measured from the first retreatment file used until no obturation material can be distinguished on the last file.
ProTaper retreatment file system left more remaining root filling material than ERE system with significant difference.
Samples obturated by TotalFill showed more remaining filling material than that filled by Adseal with significant difference.
Remnants of root filling material were left in apical and middle thirds more than coronal third with significant difference.
ProTaper retreatment file system was faster than ERE system regarding time required for retreatment with significant difference.
Regarding type of sealer, TotalFill showed more time required for retreatment than ADSEAL with non-significant difference.