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The article presents the study which examines the mechanical behaviour of four brands of engine-driven nickel-titanium endodontic instruments, HyFlex CM, Twisted File, ProFile Vortex, and RaCe. It explores the materials and methods used in the study, which involves testing of instruments for bending resistance, cyclic fatigue, torsional resistance, Vickers hardness and toughness.

Introduction: This study evaluated the cross section, resistance to bending and buckling of Reciproc and WaveOne instruments. Methods: Reciproc R25 (VDW, Munich, Germany) and WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland) instruments, all of them 25-mm long, with D0 diameter of 0.25 mm and taper of 0.08 mm/mm along the first 3 mm from the tip, had their cross section analysed and were subjected to bending and buckling resistance tests. The data from both tests were analysed using the Student t test. Results: A statistically significant difference was observed between the maximum load to bend Reciproc 25 and WaveOne Primary instruments (P < 0.05). Higher values were necessary to bend WaveOne Primary instruments when compared with Reciproc R25. In contrast, there was no statistically significant difference between the maximum load to buckle Reciproc 25 and WaveOne Primary instruments (P > 0.05). Conclusions: Both instruments exhibited similar behaviour in terms of buckling resistance. However, Reciproc R25 was more flexible, which is an important instrument property for the shaping of narrow and curved root canals. [ABSTRACT FROM AUTHOR]

Introduction: This study compared the angular deflection at failure, maximum torque, and toughness of two nickel-titanium (NiTi) instruments under torsional stress: Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland). Two NiTi instruments: Mtwo (VDW) and ProTaper (Dentsply Maillefer) served as controls. Methods: The instruments were subjected to torsional assays to evaluate the maximum torque and angular deflection at failure. A stress-strain (N × mm) curve was plotted using specific software and toughness was calculated as the integral of the area under the curve. Data obtained were statistically evaluated by ANOVA and Student-Newman-Keuls (SNK) test for multiple comparisons, with the significance level set at 5%. Results: Significant difference was observed in the angular deflection at failure for pairwise comparisons between ProTaper and the other instruments (P < 0.05). No significant differences were observed in the comparisons between the other instruments (P > 0.05). The maximum torque was ranked as follows: ProTaper > Reciproc > WaveOne > Mtwo; significant differences were observed between all instruments (P < 0.05). Differences in toughness were also detected between all instruments tested (P < 0.05), except for Reciproc versus WaveOne. Conclusion: The findings from this study revealed that Reciproc and WaveOne displayed similar mechanical behaviour in terms of angular deflection and toughness, typical of ductile metallic materials under torsion. This suggests that both instruments absorb comparable amounts of energy until fracture. Regarding torque, Reciproc exhibited the best results in comparison with WaveOne. [ABSTRACT FROM AUTHOR]

Objectives: This study evaluated the influence of reciprocating movement on the fatigue life of root canal instruments subjected to static and dynamic tests. Materials and methods: The rotary NiTi instruments used in this study were WaveOne and ProTaper F2 (both from Dentsply Maillefer, Ballaigues, Switzerland). The instruments were initially subjected to a cantilever-bending test, then to static and dynamic fatigue tests. WaveOne instruments were operated in reciprocating movement and ProTaper in continuous rotation. Results: The mean bending resistance values (maximum load in grams) of the instruments were as follows: WaveOne = 544.8; ProTaper F2 = 555.4. No significant difference was observed between the instruments tested (P > 0.05). The mean time to fracture (in seconds) of the instruments subjected to static and dynamic tests were as follows: WaveOne = 93.5 (static) and 267.6 (dynamic); ProTaper F2 = 57.8 (static) and 94.1 (dynamic). Student's t test revealed significant differences in all tests (P < 0.05). Conclusion: The findings revealed that instruments operated in a reciprocating movement and in the dynamic testing model presented prolonged fatigue life. [ABSTRACT FROM AUTHOR]

Aim: To evaluate the influence of curvature location along two artificial canals on the cyclic fatigue (CF) of two rotary instruments (Mtwo 35 and Revo-S AS35) by assessing the number of cycles to fracture (NCF) and the morphologic characteristics of the fractured instruments. Methodology: The instruments were tested in artificial curved canals made by milling grooves in stainless steel blocks, with the following measurements: 1.5 mm (width), 20 mm (total length), 3.5 mm (depth), and a U-shaped bottom. In order to enable comparisons, the parameters of curvature varied in two different designs: the canal A curvature was located at the apical portion of the canal, and the canal B curvature was located in the middle of the canal length. All instruments were rotated until fracture and the NCF was recorded. Data were analysed by Student's t test. The fractured surfaces and helical shafts of the instruments were analysed by scanning electron microscopy (SEM). Results: Canals A and B had statistically significantly different (P < 0.05) NCF values, with canal B resulting in the lowest NCF values. Plastic deformation of the shafts was not detected in any of the instruments tested. The fractured surfaces displayed morphological characteristics of ductile mode fracture. Conclusions: Placement of the curvature in the middle of the canal length reduced the NCF of the instruments tested. [ABSTRACT FROM AUTHOR]

Introduction: The goal of the present study was to evaluate the influence of surface grooves (peaks and valleys) resulting from machining during the manufacturing process of polished and unpolished nickel-titanium BR4C endodontic files on the fatigue life of the instruments., Methods: Ten electropolished and 10 unpolished endodontic files were provided by the manufacturer. Specimens were from the same batch, but the unpolished instruments were removed from the production line before surface treatment. The instruments were evaluated with a profilometer to quantify the surface roughness on the working part of the instruments. Then the files were subjected to rotating bending fatigue tests., Results: Analysis with the profilometer showed that surface grooves were deeper on the unpolished instruments compared with their electropolished counterparts. In the rotating bending fatigue test, the mean and standard deviation for the number of cycles until fracture (NCF) were greater for instruments with less pronounced grooves. Student t test revealed significant differences in all tests (P < .05)., Conclusions: The results from the present study showed that the depth of the surface grooves on the working part affected the NCF of the instruments tested; the smaller the groove depth, the greater the NCF., (Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: This study evaluated the influence of flexibility and reciprocating movement on the fatigue life of endodontic instruments subjected to static and dynamic tests., Methods: The rotary nickel-titanium instruments used in this study were Reciproc and Mtwo. The instruments were initially subjected to a cantilever-bending test and then to static and dynamic fatigue tests. Reciproc instruments were operated in reciprocating movement, whereas Mtwo instruments were worked in continuous rotation., Results: The means of bending resistance (maximum load in grams) of the instruments were 274.9 for Reciproc and 429 for Mtwo. The mean times (in seconds) to fracture of the instruments subjected to static and dynamic tests were 214.5 (static) and 286.3 (dynamic) for Reciproc and 38.9 (static) and 99 (dynamic) for Mtwo. The Student's t test revealed significant differences in all tests (P < .05)., Conclusions: The results of the present study showed longer fatigue life for instruments with higher flexibility, driven by reciprocating movement, and in the dynamic testing model. These findings reinforce the assumption that use of reciprocating movement is a means to prolong the fatigue life of rotary nickel-titanium endodontic instruments during instrumentation of curved canals., (Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: This study evaluated the influence of different features of canal curvature geometry on the number of cycles to fracture of a rotary nickel-titanium endodontic instrument subjected to a cyclic fatigue test., Methods: BioRaCe BR4C instruments (FKG Dentaire, La Chaux-de Fonds, Switzerland) were tested in 4 grooves simulating curved metallic artificial canals, each one measuring 1.5 mm in width, 20 mm in total length, and 3.5 mm in depth with a U-shaped bottom. The parameters of curvature including the radius and arc lengths and the position of the arc differed in the 4 canal designs. Fractured surfaces and helical shafts of the separated instruments were analyzed by scanning electron microscopy., Results: The Student's t test showed that a significantly lower number of cycles to fracture values were observed for instruments tested in canals with the smallest radius, the longest arc, and the arc located in the middle portion of the canal. Scanning electron microscopic analysis of the fracture surfaces revealed morphologic characteristics of ductile fracture. Plastic deformation was not observed in the helical shaft of the fractured instruments., Conclusions: Curvature geometry including the radius and arc lengths and the position of the arc along the root canal influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to flexural load., (Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)