الفهرس 
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Abstract
In these study we compared centering ability, canal transportation and ability to maintain canal curvature while using single rotary file system One shape, single file protaper F2 and reciproc R25 in reciprocation motion and continues rotation.
A total of sixty human mandibular first molar with mature apex and normal root morphology with moderate canal curvature of the mesial root 25-40 ͦ according to Schnieider were used in these study.
Samples were divided into three groups (twenty each), according to the system that used for instrumentation.
Teeth were accessed using an Endo-Access bur. Distal roots with the respective part of the crown of all samples were sectioned at the furcation level using stainless steel disc under coolant and discarded. Determination of the working length was performed at magnification 8X using a surgical microscope** by inserting #10 K-file to the mesio-buccal root canal terminus and subtracting 1 mm from the tooth length.
Specimens were mounted in rubber base impression material in six plastic trays for preoperative cone beam computerized tomography scanning (CBCT), each trey containing ten specimens to evaluate centering ability , canal transportation and ability to maintain canal curvature
The sixty sample were divided into 3 groups according to canal preparation technique : group I :20 sample were prepared with One Shape, group II :20 samples were prepared with Protaper F2 , group III :20 sample were prepared with Reciproc , each group was divided into two subgroup. Subgroup A all rotaryfiles work in reciprocatin , subgroup B all rotary files work in rotation. In the third group , Reciproc R25 instrumentation technique , the file is designed to cut during counterclockwise motions so that the Reciproc reached the apex of the canal by reciprocating movements in opposite directions (ie, counterclockwise [cutting direction] and clockwise [release of the instrument]).Because of the counter clock wise cutting angle is greater than the angle of reverse direction, the reverse movement could improve the progression of the instrument toward the apex with respect to continuous motion, so i used Silver VDW reciproc motor . I used I Endo reciprocating endodontic motor for another two groups.
Result were tabulated and statistically analyzed. The result showed that there was no statistically significant difference between three different rotary system in canal transportation, centering ability and ability to maintain canal curvature except Reciproc at 2.5 mm level showed statistically significant only in centering ability
Conclusions
Under the conditions of the study the following was concluded:
1. Reciprocation motion tended to respect the canal curvature more than continues rotation.
2. Rotation motion showed higher insignificant distal transportation.
3. One shape showed highest transportation and lowest centering