الفهرس 
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Abstract
The use of nickel-titanium (NiTi) instruments has revolutionized root canal treatment
largely because of their advanced flexibility, reduced ledge formation and the
capacity to reduce the operating time.
Cyclic fatigue is a major reason for NiTi file fractures and is considered a
complicated challenge in root canal therapy. The advantages of single-file
reciprocating systems include time saving, cost-effectivenes and low risks of
instrument fractures.
This study was conducted to examine the effect of different kinematics (reciprocation
and continuous rotation motions) on cyclic fatigue resistance of Reciproc blue file,
also the influence of different canal curvatures on cyclic fatigue resistance of
Reciproc blue file.
Materials and methods:
A total of 80 Reciproc Blue R25 NiTi files were collected and randomly divided
into four groups according to the different rotation/ reciprocation angles as follows:
• group A1: files were operated in continuous rotation motion
• group A2: files were operated in 150°CCW-30°CW reciprocating motion
• group A3: files were operated in 210°CCW-30°CW reciprocating motion
• group A4: files were operated in 90°CCW-40°CW reciprocating motion
All groups were then subdivided into two subgroups according to the simulated canal
curvature
• Subgroup B1: Files were operated in a 60° artificial canal curvature.
• Subgroup B2: Files were operated in a 45° artificial canal curvature.
All files were inspected using stereomicroscope with x30 magnification for
standardization and reliability of the experiment and for detection of any visible
deformation, there were no defective instrument to be discarded.
Summery
86All files were operated in a cyclic fatigue testing device made of tempered steel
testing block with two stainless steel artificial canals with 45° and 60° angles of
curvature, 5-mm radius and inner diameter of 1.5mm. Instruments were operated
using E-connect S Endomotor. To reduce friction as the metal instrument contacted
the metal canal walls, synthetic lubricating oil was used.
All instruments were operated until fracture occurred, the time to fracture was
recorded, the fractured fragment length was measured and the number of cycles to
fracture was calculated. Data were statistically analyzed. The fractured segment was
observed through scanning electron microscopy to evaluate type the of fracture.
Results:
The results of the present study showed that all three tested reciprocating motions
yielded a significant increase in time to failure when compared with continuous
rotation motion in both simulated canal curvatures. Furthermore, with the exception
of groups A2B1 and A3B1, there was a significant difference in the time to failure
among the three reciprocating groups in both canal curvatures.
All the experimental groups revealed a greater cyclic fatigue resistance at 45° angle
of curvature as compared to 60° angle of curvature.
Increasing the CCW angle, and consequently increasing the angle of progression for
each reciprocation cycle, reduced the resistance to cyclic fatigue.
There was no significant difference in the length of the fractured fragment for all
tested groups in both canal curvatures.
There was a non-significant correlation between all the variables (TTF, NCF and FL)
in all groups except in A2B1(150°CCW-30°CW with 60° canal curvature) and
A2B2 (150°CCW-30°CW with 45° canal curvature) reciprocating groups which
showed a high significant correlation between TTF and NCF