PubMed · 4949016
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O Hokwerda. 1971. [New ergonomic system].. https://pubmed.ncbi.nlm.nih.gov/4949016/
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The present work evaluated the influence of the curved segment length of artificial root canals (the arc) and the number of cycles necessary to fracture engine-driven nickel-titanium endodontic instruments. ProTaper F3 25-mm files at 250 rpm were used in two artificial canals. The artificial canals were made of stainless steel with an inner diameter of 1.04 mm, a total length of 20 mm, and arc on the ends with a radius of curvature of 6 mm. The arc length of the first tube measured 9.4 mm, and the straight part measured 10.6 mm. The second tube was 14.1 mm long, and the straight part measured 5.9 mm. We determined the fracture surface distances and the number of cycles necessary to induce fatigue fracture in the ProTaper F3 instruments. The fracture surfaces and the helical shaft of the instruments were investigated using a scanning electron microscope. The results indicated that the required number of cycles to cause a fracture was influenced by the canal arc length, the morphology of the fractured surface presented ductile characteristics, and plastic deformation in the helical shaft of the fractured instruments did not occur.
The purpose of this study was to compare the number of rotations to fracture of nickel-titanium (NiTi) rotary files operated at different speeds and different angles. We used 60 Profile NiTi rotary files, size 25 (30 each of 0.04 and 0.06 taper), operated at speeds of 350 or 600 rpm at angles of 25, 28, and 33.5 degrees. The time to fracture and number of rotations to fracture were recorded and calculated. A significant (p < 0.001) difference was found in the number of rotations to fracture according to taper and angle. Files of 0.06 taper fractured more readily than files of 0.04 taper. Increasing the angle at which the file was rotated decreased the number of rotations to fracture for both tapers; 0.04-taper files were more affected by an increase in the angle than the 0.06-taper files. However, the number of rotations to fracture was not related to the speed at which the files were operated.
The aim of the present study was to establish a mathematical model to characterize the flexural behavior of nickel-titanium (NiTi) rotary instruments. The bending behavior of ProFile (0.06 and 0.04 tapers), K-3 (0.06 taper), Quantec (0.04 taper) with tip size of ISO 25, was assessed by pressing the tip of the static rotary file against a smooth, freely movable, glass surface. The deflected instrument was photographed digitally, and the deflection path was digitized in software, to which data a function was fitted that best described the bending behavior of the instrument. It was found that all instruments deflected in a manner closely resembling a negative exponential function: y = A x e(-x/b). The present approach indicated that the analytical difficulties of handling the complex cross-section in tapering spirals in beam-bending theory may be circumvented by a practical and elementary curve-fitting method.