Evaluation of Cross-Sectional Designs Impact of Different NiTi Files on Distortion Resistance Using SEM (An-in Vitro Study)

Abstract—Background and aims: The aim of this study was to compare the effect of cross-sectional designs of four rotary systems (One Curve, 2Shape, K3-i File, E3 Azure), on distortion resistance of the metal surfaces of these files in simulated resin blocks under controlled conditions with five repeated usages, using scanning electron microscope (SEM). Materials & Methods: Four rotary file systems: (1) One Curve, (2) 2Shape, (3) K3-i File, and (4) E3 Azure, were tested in simulated J-shaped root canal resin blocks with a 45 ̊ angle of curvature. Ten files from each system, each one of the 10 files were used to prepare 5 resin blocks, named R1-R2-R3-R4-R5. All the used files from the 4 systems had tip size 25 diameter, taper (6%), and length (25 mm). Following the manufactural recommendation of each system. All the resin blocks were prepared for Glide Path with manual reamers size 10, and 15, with a fixed working length 16 mm, then all the samples were prepared with a Proglider rotary file from Dentsply (size 16 taper 3%), then finally were prepared with Edge Files (USA), with size 20 and taper 6%, reaching to the step of master preparation with the selected files of the 4 systems. Using a customized device for preparation to ensure fixed vertical force and to exclude any lateral force, preparation was done with EDTA solution as irrigation, with a fixed no. of 5 strokes, the time was controlled by using a Metronome, each stroke duration was 6 seconds. Five parameters were suggested to be evaluated by two observers. These parameters or criteria includes: 1) Apical deformation, 2) Cutting edge deformation, 3) Crack presence, 4) Full spiral deformation, 5) Apical spiral deformation. The data were collected and registered in the Excel sheet for all 44 files (4 instruments as control) and comparison was done between the 4 systems. Visual observation for all the images has been done, and the data registered as a scale from 1 to 4 for the first two criteria, and as present or not for the other three criteria. Results: For the apical deformation parameter, there was a non- significant difference (P > 0.05) (P value = 0.625) among all experimental groups by using the KWT. For the cutting-edge deformation parameter, there was a significant difference at (P < 0.05). For the crack parameter, there was a non-significant difference at P > 0.05 (P value = 1) among all experimental groups by using Fisher's Exact test. Conclusion: The Ni Ti alloys with heat treated technologies showed a high resistance to cutting edge deformation, cracks formation, and instrument fracture, with five repetitions of use.