الفهرس 
Cleaning of root canal systemOnly 14 pages are availabe for public view
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Abstract
SUMMARY
n an attempt to improve root canal preparation rotary nickel-titanium instruments had been introduced, whereas clinically these instruments are associated with increased risk of fracture. This risk is attributed to fatigue failure and torsional shear stresses. Failure induced by torsional shear stresses occurs when torsional shear stresses exceed the limit of the alloy leading to plastic deformation and eventual fracture. Various aspects might contribute to increase these stresses such as; excessive pressure on handpiece, wide area of contact between canal walls and cutting edge of the instrument or if canal dimension is smaller than the dimension of non-cutting tip of the instrument which leads to taper lock specially with instruments having regular taper. A new technique for root canal preparation has been recently introduced which is using reciprocating motion instead of continuous rotation motion. Upon engaging root canal wall, the counter-clockwise rotation disengages the instrument which is highly important specially in severely curved root canals. Thus reciprocating motion minimizes torsional flexural stresses, increases the canal centring ability and reduces the taper lock of the instrument in the canal wall. Also time for preparing curved root canals with the use of single-file is reduced as in this study.In this study we compared: centering ability, transportation and percentage of debris among the three groups used in this study:
IProtaper regular sequence, single file F2 used in reciprocating motion and single file F2 used in continuous rotation motion. Each group consisted of forteen samples.
Cone beam computed tomography was used to evaluate centering ability and transportation. While Stereomicroscope was used for calculating percentage of debris on dentin walls.
Results were tabulated and statistically analyzed. The results showed that, Group II (single file F2 used in reciprocating motion) resulted in the highest centering ratio, lowest transportation values and least debris percentage. On the other hand, Group I (Protaper regular sequence) resulted in lowest centering ratio, highest transportation values and highest percentage of debris on dentin wall.Group III (single file F2 used in continuous rotation motion) resulted in intermediate values in between the other two groups