A comparative study on the shaping ability of three endodontic rotary Nickel-Titanium systems and stainless- steel hand K-flexofile in simulated curved canals

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Background: The purpose of this study is to compare the Shaping ability of three rotary endodontic nickel-titanium systems (Pro- File, CT and Protaper) with stainless steel hand K-flexofile in simulated curved canals at different levels, this include total canal diameter, outer and inner transportations and centering ratio (the ability of the instruments to remain centered in the shaped canals). Materials and method: Eighty simulated curved canals made of clear polyester resin were used to assess instrumentation.The acrylic blocks were divided into four groups, 20 simulated canals for each group were enlarged from #10 to # 25. In the first three groups all NiTi rotary instruments were set into a permanent rotation with a 16:1 reduction handpiece powered by a torque- limited electric motor set at 300 rpm. All the instruments were used in a crown down manner using a gentle in-and-out (peck- ing) motion. In the fourth group the simulated canals were instrumented with stainless steel K-flexo-files by using balanced force technique. Each simulated canal was filled with a drawing ink using to increase the color contrast for photographic documentation. Photographs of the unprepared canals were taken by the aid of stereomicroscope and digital camera at magnification of 40 times. When instrumentation of the canals was completed, the canals were injected again with the drawing ink and the image proce- dure is repeated. Pre- and postoperative digital photographs of the resin blocks were accomplished using Adobe Photoshop CS2 software program. At this stage the amount of resin removed i.e. the difference between the canal configuration before and after instrumentation was determined for both the inner and the outer side of the curvature at five reference points. Results: For total canal diameter there was highly significant difference among the four groups at all levels. For outer canal trans- portation there was highly significant difference among the four systems at all levels except at the second level where the differ- ences were not significant. For inner transportation there was highly significant difference among the four groups at all levels. For centering ratio there was highly significant difference among the tested groups at all level. Conclusion: K-flexofile scored the maximum canal diameter at the apical two levels. ProTaper prepared the largest canal diameter at all levels. In comparison with ProTaper, canals prepared by GT and ProFile maintained original curvature was better with less straightening. The ability of instruments to remain centered in prepared canals was significantly better in NiTi systems than K- flexofiles. ProTaper files have lower centering ability than GT and ProFile.