Objective: This study aimed to compare the fracture resistance of human mandibular premolar roots after instrumentation with different nickel–titanium (NiTi) Rotary systems. Methods: Forty extracted human mandibular premolars were decoronated and randomly assigned to four groups (n=10). Group 1 served as an uninstrumented control, while Groups 2–4 were prepared using different NiTi Rotary systems according to the manufacturers’ protocols: One Curve (OC) single-File system (Group 2), XP-Endo Shaper (XPS) single-File system (Group 3), and ProTaper NEXT (PTN) multi-File system (Group 4). All instrumented canals were obturated with gutta-percha and AH Plus sealer using the lateral compaction technique. Vertical fracture resistance was then tested with a universal testing machine. Data were analyzed using one-way ANOVA followed by Tukey’s post hoc test (α=0.05). Results: ANOVA revealed a significant difference in fracture resistance among the groups (P=0.005). The control group (402 ± 115.93 N) showed significantly higher mean fracture resistance compared to all instrumented groups (P < 0.05). Among the instrumented groups, XPS (304 ± 37.47 N) had the highest mean fracture resistance, followed by OC (291 ± 78.37 N) and PTN (288 ± 50.50 N), but these differences were not statistically significant (P > 0.05). Conclusions: Root canal instrumentation with both single-File and multi-File NiTi Rotary systems significantly reduced fracture resistance compared to uninstrumented roots. There was no significant difference in fracture resistance between the single-File and multi-File systems, indicating that the single-File approach does not provide an advantage in preserving root strength.

Objectives: Cleaning and shaping of the root canal system is an important step in endodontic therapy. New instruments incorporate new preparation techniques that can improve the efficacy of cleaning and shaping. The aim of this study was to compare the efficacy of Mtwo and RaCe Rotary File systems in straightening the canal curvature using only one File or the conventional method.Materials and Methods: Sixty mesial roots of extracted human mandibular molars were prepared by RaCe and M two nickel-titanium (NiTi) Rotary Files using the conventional and only one Rotary File methods. The working length was 18 mm and the curvatures of the root canals were between 15-45o. By superimposing x-ray images before and after the instrumentation, deviation of the canals was assessed using Adobe Photoshop CS3 software. Preparation time was recorded. Data were analyzed using three-way ANOVA and Tukey’s post hoc test.Results: There were no significant differences between Ra Ce and M two or between the two root canal preparation methods in root canal deviation in buccolingual and mesiodistal radiographs (P>0.05). Changes of root canal curvature in>35o subgroups were significantly more than in other subgroups with smaller canal curvatures. Preparation time was shorter in one File only technique.Conclusion: According to the results, the two Rotary systems and the two root canal preparation methods had equal efficacy in straightening the canals, but the preparation time was shorter in one File only group.

Background and Aim: Cleaning and shaping is one of the important steps in endodontic treatment, which has an important role in root canal treatment outcome. This study evaluated the rate of File fracture and File deformation in Neolix Rotary system and K-Files in shaping of the mesiobuccal canal of maxillary first molars with moderate curvature. Materials and Methods: In this ex vivo experimental study, the mesiobuccal root curvature of maxillary first molars was measured by the Schneider’, s method, and canal preparation was performed in 2 groups of 30 with Neolix Rotary system and manual K-Files. To determine the fracture rate of Files, a File was used until it broke or deformed, and the number of canals cleaned by that File was recorded. The data were analyzed by the Mann-Whitney U test. Results: File fracture rate in the Rotary group was slightly higher than that in the manual K-File group but, the frequency of File deformation in manual K-Files was slightly more than that in the Rotary group. There was no statistically significant relationship between File type and frequency of File fracture or deformation (P>0. 05). Conclusion: Manual stainless steel K Files and Neolix NiTi Rotary Files were the same in terms of File fracture and File deformation in preparation of canals with moderate curvature.

Introduction: This study was carried out to compare the capability of K-Files with Mtwo Rotary File in tenns of negotiation as well as depth of penetration in second mesiobuccal (MB2) canal of maxillary first molar. Materials and Methods: Atotal of 32 MB2 canal of maxillary first molars having different root curvatures (not more than 30 degree) and root lengths were selected and then detected by K-File #10, #8 and #6. Based upon File penetration the samples were assigned into four groups. Group A:K-File#10 penetrate>2 mm into coronal third, group B:K-File#10 could penetrate<2mm into coronal third, continue proceeding with #8 which had>2mm penetration, group C: K-Files #10 and 8 could penetrate<2mm, continue proceeding with #6 for deeper penetration, and group D: Mtwo File #10/.04 was applied into all three above groups until resistance was felt. Finally, accurate working lengths at each group after K-File #10 insertions into the canal were determined radiographically. The mean depths of root canal penetration were analyzed statistically using Duncan test by SAS software (version 9.1) in GLM procedure.Results: The mean of initial penetration for #10 Mtwo Files was 19.16mm, whilst it was 7.72 mm for K-File #6, 10.72 mm for K-File #8, and 12mm for K-File#10. The difference between Mtwo Rotary Files and hand K-Files was statistically significant (P<0.01).Conclusion: Mtwo Rotary Files could be an efficient substitute for hand Files to negotiate MB2 canal both more easily and rapidly. Toour knowledge, it is the first time that a NiTi Rotary File showed success in negotiation of any canal.

Introduction: Use of Rotary Files in root canal preparation is inevitable due to their high speed and reduced duration of treatment. However, microcracks and even root fracture may sometimes occur in teeth where canal(s) is/are prepared using these devices. The purpose of the current study was to compare NeoNiti single-File with RaCe multi-File Rotary systems. Materials and Methods: An accurate scanner designed detailed three-dimensional File models, and a simulated model was developed using canal-specific features; including dentin thickness, root canal length, taper rate and root canal curvature. Cleaning and shaping conditions were simulated with appropriate speed and crack conditions for both types of Files on the computer. Strain accumulation sites in the root dentin wall where microcracks was likely to occur were simulated and investigated. Abaqus and ANSYS software were used to perform finite element simulations. Results: RaCe Files with 0. 04 taper caused the lowest level of stress (34. 33 MPa) to the simulated canal. Conversely, the highest level of stress (62. 35 MPa) was applied by 8% NeoNiti File to the simulated canal. Conclusions: Based on the present experimental study, it can be concluded that RaCe multi-File Rotary system may better be used in endodontic therapy, and the risk of microcracks in the tooth wall is less than that of NeoNiti single-File Rotary system.

Introduction: The aim of this study was to evaluate the efficacy of two Rotary instrument systems (ProTaper and Revo-s File) in removing calcium hydroxide residues from root canal walls. Materials and Methods: Thirty human maxillary incisors were instrumented with the ProTaper System up to the F2 instrument, irrigated with 2. 5% NaOCl, and filled with a calcium hydroxide intracanal dressing. After 7 days, the calcium hydroxide dressing was removed using the following Rotary instruments: G1-NiTi size 25, 0. 06 taper, of the Revo-s File System,G 2-NiTi size 25, 0. 06 taper, of the protaper File System. The teeth were longitudinally grooved on the buccal and lingual root surfaces, split along their long axis, and their apical and cervical canal thirds were evaluated by SEM (×1000). Results: The images were scored and the data were statistically analyzed using the Kruskall Wallis test. None of the instruments removed the calcium hydroxide dressing completely, either in the apical or cervical thirds, and no significant differences were observed among the Rotary instruments tested (p > 0. 05). Conclusion: To achieve the best adaptation of filling material after root canal treatment, it is crucial to remove intracanal medication from the root canal walls. However, none of the irrigation regimens and different techniques were able to completely remove the CH from the root canal wall.

Objectives: The purpose of this study was to evaluate the resistance to fatigue failure of five different nickel-titanium Rotary Files in three different curved trajectories.Materials and Methods: A total of 150 Neoniti A1, RaCe 25.06, Mtwo 25.06, Twisted File 25.06 and ProTaper Next X2 Files with the tip size of 25 were tested (n=30 for each group). Three groove types simulating curved canals were used differing in radius, arc length and position of the arc, each measuring 1.5 mm in width, 20 mm in total length and 2.5 in depth. Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure. Furthermore, the fragment length of the fractured tips and angle and radius of curvature formed by each File in each trajectory were evaluated. The data were analyzed by t-test, one way ANOVA and Tukey’s HSD test.Results: Neoniti showed the highest and RaCe showed the lowest number of cycles to fracture (NCF) values (P<0.05), indicating the highest and lowest fatigue resistance, respectively. The highest and lowest curvature angles were seen in RaCe and Neoniti, respectively. Regarding the radius of curvature, Twisted File had the lowest and Neoniti had the highest values. The mean NCF of all Rotary Files was lower in the more coronally curved trajectory.Conclusion: The fatigue resistance of the evaluated Rotary Files was lower in more coronally located curvatures. Neoniti exhibited the highest and RaCe exhibited the lowest fatigue resistance compared to other evaluated Files.

Objectives: During root canal preparation, apical extrusion of debris can cause inflammation, flare-ups, and delayed healing. Therefore, instrumentation techniques that cause the least extrusion of debris are desirable. This study aimed to compare apical extrusion of debris by five single-File, full-sequence Rotary and reciprocating systems.Materials and Methods: One hundred twenty human mandibular premolars with similar root lengths, apical diameters, and canal curvatures were selected and randomly assigned to six groups (n=20): Reciproc R25 (25, 0.08), WaveOne Primary (25, 0.08), OneShape (25, 0.06), F360 (25, 0.04), Neoniti A1 (25, 0.08), and ProTaper Universal. Instrumentation of the root canals was performed in accordance with the manufacturers’ instructions. Each tooth's debris was collected in a pre-weighed vial. After drying the debris in an incubator, the mass was measured three times consecutively; the mean was then calculated. The preparation time by each system was also measured. For data analysis, one-way ANOVA and Games-Howell post hoc test were used.Results: The mean masses (±standard deviation) of the apical debris were as follows: 2.071±1.38mg (ProTaper Universal), 1.702±1.306mg (Neoniti A1), 1.295±0.839mg (OneShape), 1.109±0.676mg (WaveOne), 0.976±0.478mg (Reciproc) and 0.797±0.531mg (F360). Compared to ProTaper Universal, F360 generated significantly less debris (P=0.02). The ProTaper system required the longest preparation time (mean=88.6 seconds); the Reciproc (P=0.008), OneShape (P=0.006), and F360 (P=0.001) required significantly less time (P<0.05).Conclusions: All instruments caused extrusion of debris through the apex. The F360 produced significantly less debris than did the ProTaper Universal.