TY - JOUR ID - TI - The shaping effects of three rotary Nickel-Titanium systems in simulated curved canals AU - Hamid Kassim حميد قاسم AU - Abdul Karim J. Al-Azzawi عبد الكريم العزاوي PY - 2012 VL - 24 IS - 3 SP - 1 EP - 7 JO - Journal of baghdad college of dentistry مجلة كلية طب الاسنان بغداد SN - 18171869 23115270 AB - Background: The purpose of this study is to compare three rotary endodontic nickel-titanium systems (ProFile,GT and ProTaper) with stainless steel hand K-flexofile in simulated curved canals at different levels, thisincludes: Incidence of canal aberrations (apical zipping associated with elbow, ledge and perforation), Changes ofworking length, Preparation time for each system and Breakage and permanent deformation of instruments.Materials and method: Eighty simulated curved canals made of clear polyester resin were used to assessinstrumentation. The acrylic blocks were divided into four groups, 20 simulated canals for each group were enlargedfrom #10 to # 25. In the first three groups all NiTi rotary instruments were set into a permanent rotation with a 16:1reduction hand piece powered by a torque-limited electric motor set at 300 rpm. All the instruments were used in acrown down manner using a gentle in-and-out (pecking) motion. In the fourth group the simulated canals were instrumentedwith stainless steel K-flexo-files by using balanced force technique. Each simulated canal was filled with a drawing inkusing to increase the color contrast for photographic documentation. Photographs of the unprepared canals weretaken by the aid of stereomicroscope and digital camera at magnification of 40 times. When instrumentation of thecanals was completed, the canals were injected again with the drawing ink and the image procedure is repeated. Preandpostoperative digital photographs of the resin blocks were accomplished using Adobe Photoshop CS2 softwareprogram. At this stage the amount of resin removed i.e. the difference between the canal configuration before and afterinstrumentation was determined for both the inner and the outer side of the curvature at five reference points.Assessments were made under the stereomicroscope according to the presence of different types of canalaberrations (apical zip associated with elbow, ledge and perforation). The changes of working length weredetermined by subtracting the length of master apical file from the original length (16mm). The time taken toprepare each canal was recorded in minutes with the aid of a stop timer. Throughout the study a record was kept ofthe numbers and sizes of instruments that fractured or became permanently deformed during use.Results: there were significant differences among the groups, even though more zips and ledge werecreated with K-flexofile followed by ProTaper. NiTi instruments caused a significantly greater loss of working lengththan K-flexofile; while there was no significant difference among NiTi groups. The shortest mean of preparationtime was recorded when ProTaper were used; while the longest time was documented for GT. No permanentdeformation occurred with NiTi groups. None of the stainless steel K-flexofile was separated.Conclusion: K-flexofiles created significantly more aberration than NiTi systems. ProTaper caused moremorphological changes compared with ProFile and GT systems. Small mean changes in working lengthoccurring with rotary NiTi instruments. The preparation time of ProTaper was faster than with other groups.NiTi instruments may be more susceptible to separation than stainless-steel instruments. Most failures of the handstainless-steel files were deformations rather than fractures. Fracture rate was approximately 30% for ProTaper,16.6% for GT and 8.3% for Profiles.

ER -