الفهرس 
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Abstract
The purpose of this study was to compare canal transportation and centering ability of three rotary NiTi systems (RaCe, TF and GTX) files.
Sixty canals were selected and divided into three groups (each of twenty). Each group was subdivided into two groups depending on canal curvature (moderate and severe). After preparation with RaCe, TF and GTX NiTi instruments, the amount of transportation were assessed by cone beam computed tomography (CBCT).
Four sections (1.3 mm, 2.6 mm, 5.2 mm, and 7.8 mm) from the apex were recorded.
The three groups were statistically analyzed through comparing pre and post instrumentation CT at the four levels.
Values obtained for assessment of remaining dentin thickness and changes in the curvature of root canals were statistically analyzed.
Regarding transportation, results could be summarized as follows:
1.There was no statistically significant difference between the three systems at different levels of root canals. While RaCe in subgroup A, showed highest statistically significant canal transportation at 5.2mm and 7.8 mm levels than TF and GTX. In subgroup B, RaCe showed highest statistical significant canal transportation at 7.8 mm than TF and GTX. .
2.There was no statistically significant difference between sub groups in all systems.
3.In the RaCe group; in sub groups A & B, the highest statistical significant canal transportation was found at 7.8mm level followed by 5.2 mm level, they were statistically significantly higher when compared to 2.6mm and 1.3 mm levelsthere was no statistically significant difference in Subgroup A between means ± SD values of dentin thickness at different levels of root canals (P>0.05). While in Subgroup B, the mean dentin thickness at the coronal levels (7.8 mm and 5.2 mm) was statistically significantly higher when compared to the other two levels (2.6 mm and 1.3 mm). In sub group B at 7.8mm in level showed higher statistical significant canal transportation followed by 5.2 mm in level than 2.6mm 1.3 mm of lower canal transportation.
4.In the TF, Canal transpiration at 7.8 mm and 5.2 mm was statistical significant lower than race system. there was no statistically significant difference in canal transportation at different levels in in subgroupsubgroups A & B.: statistical significant lower canal transportation than race system.
5.In the GTX, Canal transpiration at 7.8 mm and 5.2 mm was statistical significant lower than race system. there was no statistically significant difference at different levels in subgroupsubgroups A & B.: statistical significant lower canal transportation than race system.
Regarding canal centering ability:
1.There was no statistically significant difference in canal centering ability at different levels of root canals. While, it was found that TF and race GTXand 5.2 mm showed the highest statistically significant centering ability at 7.8mm than RaCe,.e showed the lowest centering ability.
2.There was no statistically significant difference between subgroups in all systems.
3.In the RaCe group; in subgroup A, there was no statistically significant difference in in Subgroup A canal centering abilitybetween means ± SD values of canal centering ratio dentin thickness at different levels of root canals. While Iin Subgroup B, the highest statistically significant canal centering ability was found at 1.3mm level and 2.6mm, Theyco2.6 mm, 5.2 mm and 7.8 statistically significantly higher when compared to 5.2 mm and 7.8mm levels1.3 mm.
4.In the TF; subgroups A and B there was no statistically significant difference in between means ± SD values of canal centering ability at different levels of root canals.
5.In the GTX; subgroup A, the highest statistically significant canal centering ability was found at the 2.6 mm, 5.2 mm and 7.8 mm levels, they were statistically significantly higher when compared to 1.3 mm level. While in subgroup B, there was no statistically significantdifference between means ± SD values of in canal centering ability at different levels of root canals.