الفهرس 
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Abstract
The aim of the present study was to compare the shaping ability of one curve and HyFlex EDM rotary file systems regarding Canal curvature, Canal centering ability and Canal Transportation.
Forty human permanent mandibular first molars were selected with mature apices having angles of curvature of the mesiobuccal canals ranging between 20° to 40° degrees from the buccal view. Samples were randomly and equally distributed into two groups each of text according to the system used for mesiobuccal canal preparation Cone beam computed tomography was used to evaluate angle of canal curvature and dentin thickness pre and post instrumentation. Dentin thickness was measured at three different levels 3,6 and 9 mm from the apex at axial view using measuring tool.
Canal angle was determined according to scheinder method and Percent of reduction of canal curvature was calculated according to following equation
(pre instrumentation measurement-post instrumentation measurment )/(pre instrumentation measurement) x100
Canal transportation and centering was calculated according to following equations
Degree of transportation in mesio-distal direction was calculated using the folllowing equation
(Y1 - Y2) - (Y´1- Y´2)
Centering ratio was calculated for all groups mesio-distally using the following equations:
D= (Y1 - Y´1) / (Y2 - Y´2)
Where:
where D is the mesiodistal measurement and,
Y1= shortest distance from the mesial aspect of the root to the periphery of the uninstrumented canal.
Y´1= shortest distance from the mesial aspect of the root to the periphery of the prepared canal.
Y2= shortest distance from the distal aspect of the root to the periphery of the uninstrumented canal.
Y´2= shortest distance from the distal aspect of the root to the periphery of the prepared canal.
Degree of transportation in buccolingual direction was calculated using the folllowing equation
(X1 - X2) - ( X1´- X´2)
Centering ratio was calculated for all groups buccolingual using the following equations
C= (X1 – X´1) / (X2 - X´2)
where C is the buccolingual measurement and,
X1= shortest distance from the buccal aspect of the root to the periphery of the uninstrumented canal.
X´1= shortest distance from the buccal aspect of the root to the periphery of the prepared canal.
X2= shortest distance from the lingual aspect of the root to the periphery of the uninstrumented canal
X´2= shortest distance from the lingual aspect of the root to the periphery of the prepared canal.
Results showed that there was no statistically significant difference between different groups regarding percentage of reduction of canal curve, canal transportation and canal centering.