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Influence of Previous Angular Deformation on Cyclic Fatigue Resistance of K3XF Instruments

University of British Columbia

Objective: To evaluate the effect of preloading various degrees of the maximum distortion angle on the cyclic fatigue resistance of post-machining heat-treated nickel-titanium (NiTi) instruments. Methodology: New K3XF and K3 NiTi instruments (size 25/.04 taper)( n = 15) were tested to obtain the mean number of cycles to failure (Nf) using a 3-point bending apparatus. Torque and distortion angles at failure were determined according to the ISO 3630-1 standard. New files were then pre-cycled to four conditions (0%, 25%, 50%, and 75% of the angular deflection) and fatigue resistance tests were performed. After torsional preloading, the total number of revolutions to failure (Nf) was measured for each file. The fracture surface of each fragment was examined with a scanning electron microscope. The crack-initiation sites and the percentage of dimple area of the whole fracture cross-sectional area were recorded. Results: The fatigue resistance of K3XF instruments was two times higher than that of K3 instruments (P < 0.05). The angles of rotation at fracture of unused K3XF instruments were similar to those of K3 instruments. With both the K3 and K3XF instruments, the 25%, 50% and 75% torsional preloading groups had significantly lower Nf than the no preloading group (P < 0.05). The K3XF instruments had significantly higher Nf than the K3 in all corresponding preloading groups (P < 0.05). The fracture surface of the K3XF and K3 instruments in which the fatigue test was applied after an incomplete torsional test was characterized as the fatigue fracture pattern. iii Conclusions: The fatigue resistance of K3XF instruments was higher than that of K3 instruments. The K3XF instruments displayed a similar torque resistance to the K3 instruments. A small amount of torsional preloading reduced the fatigue resistance of both the K3 and K3XF instruments.

Text

2014-07-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/48595

Craniofacial Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/