A/B The cutting edge angle between the instrument axis and the cutting edge provides information about the clinical effectiveness and mechanism of action. With an angle <45 ', the rotating-scraping technique is recommended. This is especially true for reamers, which are used with a pulling and rotating movement out of the canal. A square profile is more stable. With its chip space (36%), considerably less material is transported out of the canal. The triangular cross-section is more flexible and has a larger chip space (60%).

C The cross-section of an H file with milled spirals permits a chip space of 35%, and the cutting edge angle is 60-65 '.

D After insertion of K files into the canal, circular as well as up and down movements are used to remove dentin.

E Following insertion of the Hedstrom file, dentin is removed using light quarter turns and apical-coronal movements circumferen-tially.

F Reamers are used with right or left counterclockwise rotation as well as up and down movements.

G Special form of a Gates drill, as well as the new nickel-titanium files exhibiting more severe conicity.

H The simple helicoid cross-section of the Hedstrom file is exhibited as a double helix in the S file.

I NiTi files exhibit a U-shaped or a modified triangular cross-section.

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