Morphometric analysis of shank-to-flute ratio in rotary nickel-titanium files

Aim To evaluate the shank-to-flute ratio in rotary nickel-titanium (Ni-Ti) instruments. Methodology The cutting portion of 15 size 30 NiTi rotary instruments. ProFile .04, ProFile .06, Pow R.02. Pow R .04 and Quantec series 2000, were examined. The handles of the instruments were fixed to a bench and supported by a removable resin base. The cutting portion was then manually abraded with abrasive strips along one aspect of their length. All instruments were fixed in a stub that permitted the adaptation and inspection of six instruments at the same time. A scanning electron microscope (SEM; Phillips model XL 20; Eindhmoven, the Netherlands) at x60 magnification was used to collect cross-sectional measurements of the shank and the flutes at the first, third and fifth flutes from the tip. The software AUTOCAD 2000 was used to measure these areas. Results The shank percentage value was, on average, equal to or greater than the flute percentage value at the sites analyzed. A regular and proportional pattern of increase of shank and flute measurements, as well as the ratio between them, was preserved. There was no significant difference between instruments and between flute sites on the same instrument (P > 0.05). However, the Quantec instruments had a flute area twice the flute area of the other instruments. Conclusions The instruments had a shank percentage measurement value equal to or greater than the flute percentage value; the cross-sectional shank-to-flute ratio was preserved. The instruments had similar shank areas, but the flute area of the Quantec instruments was twice their shank area; i.e. the design of the Quantec files provides longitudinal reinforcement by means of a gain in flute area.