الفهرس 
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Abstract
The purpose of the study was to compare the cutting efficiency and surface topography of two rotary nickel titanium instruments: Revo S and RaCe rotary systems. This study consisted of two parts:
Part I: Cutting efficiency evaluation; this was done using gravimetric analysis and by comparing the mean weight of debris generated for each system.
Part II: Surface topography of the files # 25, 0.06 taper of each system were examined before use, after two uses and after five uses by scanning electron microscopic examination.
In part I of the study, sixty extracted lower molar teeth were used; teeth were divided into two groups according to the rotary system used, then subdivided into two subgroups according to the degree of curvature (15o – 25o )and (26o – 35o). Each subgroup consisted of fifteen teeth. Teeth were weighted pre instrumentation and post instrumentation, the mean weight loss was calculated and considered as a measure of cutting efficiency, also the mean debris weight generated was calculated and considered as a measure of cutting efficiency.
In part II of the study, the SU files# 25,0.06 taper in each sub group of the Revo S system and files# 25 0.06 taper in each subgroup of the RaCe system were examined under scanning electron microscope before use, after two uses and after five uses.
Results of part I of the study, showed that there was significant difference between the Revo S and the RaCe systems, with the Revo S showing higher cutting efficiency with mild curvature (15o – 25o), although such variance was not found with moderate curvature (26o – 35o). The study also has showed that although the differences between the systems; Revo S and RaCe systems have both showed higher cutting efficiency with mild curvatures (15o – 25o) when compared with moderate curvatures (26o – 35o).
Results of part II of the study, showed that the unused RaCe files showed manufacture defects as rolling, pitting and cracks that worsen with usage. Whereas, the surface of unused Revo S files had noticeably much less defects apart from minor pitting. Defects as rolling, notched edge, pitting, cracks and straightening were clear after five uses with higher prevalence in the RaCe files. Although Revo S files show better surface characteristics than RaCe files, yet they both showed fracture after five uses.