8. Comparator group: If the system to by used is Wave One the canal preparation is done by primary file size 25 taper 8% in narrow or curved canals if size 10 K file (Mani Inc., Japan) is passively fit in the canal ( most of canals ) , but in case of K-file (Mani Inc., Japan) size 20 loose in the canal so we choose large large file size 40 taper 8% either of them to the full working length with pre programmed motor (X-Smart Plus (Dentsply) with reducing hand piece 6:1 more anticlockwise angle than clock wise one .