Influence of the Geometry of Curved Artificial Canals on the Fracture of Rotary Nickel-Titanium Instruments Subjected to Cyclic Fatigue Tests (original) (raw)
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Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 2011
Objectives. This study evaluated the effects of curvature location along an artificial canal on cyclic fatigue (CF) of an Mtwo rotary instrument, verifying the number of cycles to fatigue fracture (NCF) and morphologic characteristics of the fractured instruments. Study design. CF testing of instruments was performed in artificial canals with curvature radii of 10 mm and arc lengths of 11 mm. Mtwo rotary instruments size 40, 0.04 taper were used in 2 groups (n ϭ 10): group A, curvature positioned on middle part; group B, apical curvature. All instruments were rotated until fracture. The number of cycles to failure was registered. Data were analyzed by independent sample t test. Fractured surfaces and the helical shafts of the instruments were analyzed by scanning electron microscopy. Results. NCF for groups A and B had significant statistic differences (P Ͻ .05). The highest values were found in the group where the curvature was positioned on the apical part of the canal. No plastic deformation was observed on the helical shafts. Conclusions. The number of cycles to fracture of the Mtwo instruments increased when the arc was changed from the middle to the apical part of the canal. The morphologic characteristics of the fractured surfaces were of the ductile type.
Restorative Dentistry & Endodontics
Objectives: To compare the flexural cyclic fatigue resistance and the length of the fractured segments (FLs) of recently introduced M-Pro rotary files with that of RaCe rotary files in curved canals and to evaluate the fracture surface by scanning electron microscopy (SEM). Materials and Methods: Thirty-six endodontic files with the same tip size and taper (size 25, 0.06 taper) were used. The samples were classified into 2 groups (n = 18): the M-Pro group (M-Pro IMD) and the RaCe group (FKG). A custom-made simulated canal model was fabricated to evaluate the total number of cycles to failure and the FL. SEM was used to examine the fracture surfaces of the fragmented segments. The data were statistically analyzed and comparisons between the 2 groups for normally distributed numerical variables were carried out using the independent Student's t-test. A p value less than 0.05 was considered to indicate statistical significance. Results: The M-Pro group showed significantly higher resistance to flexural cyclic fatigue than the RaCe group (p < 0.05), but there was no significant difference in the FLs between the 2 groups (p ≥ 0.05). Conclusions: Thermal treatment of nickel-titanium instruments can improve the flexural cyclic fatigue resistance of rotary endodontic files, and the M-Pro rotary system seems to be a promising rotary endodontic file.
Influence of Rotational Speed on the Cyclic Fatigue of Rotary Nickel-Titanium Endodontic Instruments
Journal of Endodontics, 2009
Introduction: During the preparation of curved canals, rotary nickel-titanium (NiTi) instruments are subjected to cyclic fatigue, which can lead to instrument fracture. Although several factors may influence the cyclic fatigue resistance of instruments, the role of the rotational speed remains uncertain. This study was intended to evaluate the effects of rotational speed on the number of cycles to fracture of rotary NiTi instruments. Methods: ProTaper Universal instruments F3 and F4 (Maillefer SA, Ballaigues, Switzerland) were used in an artificial curved canal under rotational speeds of 300 rpm or 600 rpm. The artificial canal was made of stainless steel, with an inner diameter of 1.5 mm, total length of 20 mm, and arc at the end with a curvature radius of 6 mm. The arc length was 9.4 mm and 10.6 mm on the straight part. The number of cycles required to fracture was recorded. Fractured surfaces and the helical shafts of the fractured instruments were analyzed by scanning electron microscopy. Results: The results showed approximately a 30% reduction in the observed number of cycles to fracture as rotational speed was increased from 300 to 600 RPM (p < 0.05). The morphology of the fractured surface was always of ductile type, and no plastic deformation was observed on the helical shaft of fractured instruments. Conclusions: The present findings for both F3 and F4 ProTaper instruments revealed that the increase in rotational speed significantly reduced the number of cycles to fracture. (J Endod 2009;35:1013-1016
Survival Analysis of Factors Influencing Cyclic Fatigue of Nickel-Titanium Endodontic Instruments
Advances in Materials Science and Engineering, 2015
Objective. The aim of this study was to validate a survival analysis assessing the effect of type of rotary system, canal curvature, and instrument size on cyclic resistance.Materials and Methods. Cyclic fatigue testing was carried out in stainless steel artificial canals with radii of curvature of 3 or 5 mm and the angle of curvature of 60 degrees. All the instruments were new and 25 mm in working length, and ISO colour coding indicated the instrument size (yellow for size 20; red for size 25).Wizard Navigatorinstruments,Mtwoinstruments,ProTaperinstruments, andRevo-Sinstruments were passively rotated at 250 rotations per minute, and the time fracture was being recorded. Subsequently, fractographic analysis of broken tips was performed by scanning electron microscope. The data were then analysed by the Kaplan-Meier estimator of the survival function, the Cox proportional hazards model, the Wald test for regression covariates, and the Wald test for significance of regression model.Co...
Journal of Endodontics, 2011
Introduction: The aim of this study was to evaluate, by static and dynamic cyclic fatigue tests, the number of cycles to fracture (NCF) 2 types of rotary NiTi instruments: Twisted File (SybronEndo, Orange, CA), which is manufactured by a proprietary twisting process, and RaCe files (FKG Dentaire, La Chaux-de-Fonds, Switzerland), which are manufactured by grinding. Methods: Twenty Twisted Files (TFs) and 20 RaCe files #25/.006 taper instruments were allowed to rotate freely in an artificial curved canal at 310 rpm in a static or a dynamic model until fracture occurred. Results: Measurements of the fractured fragments showed that fracture occurred at the point of maximum flexure in the midpoint of the curved segment. The NCF was significantly lower for RaCe instruments compared with TFs. The NCF was also lower for instruments subjected to the static test compared with the dynamic model in both groups. Scanning electron microscopic analysis revealed ductile morphologic characteristics on the fractured surfaces of all instruments and no plastic deformation in their helical shafts. Conclusions: Rotary NiTi endodontic instruments manufactured by twisting present greater resistance to cyclic fatigue compared with instruments manufactured by grinding. The fracture mode observed in all instruments was of the ductile type. (J Endod 2011;37:1553-1557
Journal of Stomatology, 2024
Introduction Despite improvement in endodontic file technology, breakage continues to occur. In this study, cycle fatigue resistance and fragment length were evaluated for ProTaper Ultimate, AF-F ONE, and ProTaper Gold instruments in single- and double-curved canals at 37 ± 1°C. Objectives The objective of the current study was to evaluate the resistance of cyclic fatigue and fragment length of ProTaper Ultimate, AF-F ONE, and ProTaper Gold rotary nickel-titanium instruments Material and methods Ninety NiTi rotary instruments were divided into three groups: ProTaper Ultimate, AF-F ONE, and ProTaper Gold. Based on single or double curvature, each group had two sub-groups (n = 15). Double-curved canal was characterized by a 60-degree coronal bend, 5-millimeter radius, with additional 70-degree apical curvature, 2 mm radius. Single-curved canal had a 60-degree angle and radius of 5 millimeters. Stainless steel blocks were maintained at 37 ± 1°C in a computerized water bath. Time to fracture was noted, and the number of cycles to failure was evaluated. Length of fractured sections was assessed, and scanning using electron microscopy was performed. Results A significant difference in cycles to failure was seen in AF-F ONE instrument compared with other groups in single- and double-curved canals (p < 0.05). No significant differences between ProTaper Ultimate and ProTaper Gold in either canal type (p > 0.05) were observed. The double-curved canal had fewer fracture cycles than the single-curved in all examined files, as shown by independent t-test (p < 0.05). No notable distinction was noted in the length of fractured segments within single- and double-curved artificial canals (p > 0.05), but it was substantially shorter in double-curved ones (p < 0.05). Conclusions The AF-F ONE instrument demonstrated superior cyclic fatigue resistance compared with ProTaper Gold and ProTaper Ultimate in either canal type.
Acta Biomedica, 2023
Background: The study was planned to compare the cyclic fatigue resistance of 3 different heat-treated Ni-Ti files in rotary motion utilizing cyclic fatigue testing device. Materials and method: Three nickel-titanium rotary systems namely, Hero Gold, NeoEndo Flex and T-Pro are used in this study. Ten files from each file system with 0.04% taper, #25 size and 21mm length are tested for cyclic fatigue resistance. The test is conducted in an artificial canal in customized cyclic fatigue device. The canal system, comprises of two adjustable stainless-steel blocks which have 3 mm width, 60° angle of curvature located 8mm from the tip. The file is rotated with respective RPM and torque until fracture, synchronized with timing by a digital stopwatch. For each file, the time to fracture is recorded in seconds and the number of cycles to fracture (NCF) is calculated by multiplying the time (seconds) to fracture by the number of RPM and length of the fractured fragment recorded. Data is analysed using one-way analysis of variance (ANOVA).Results: Hero Gold group had a higher mean time to fracture followed by NeoEndo Flex and T-Pro files (P<0.05). There is no significant difference between length of the fractured fragment (P>0.05).Conclusion: Hero Gold exhibited greater cyclic fatigue resistance compared to other rotary files, Hero Gold had superior cyclic fatigue resistance which is helpful in increasing the number of cycles of usage during root canal treatment.
Predicting in vivo failure of rotary nickel-titanium endodontic instruments under cyclic fatigue
Dental Materials Journal, 2012
The aim of this study was to examine the lifespan or number of cycles to failure of tapered rotary nickel-titanium (Ni-Ti) endodontic instruments. Simulated root canals with different curvatures were used to determine a relation between canal curvature and instrument lifespan. Using a novel mathematical model for the deformation of pseudoelastic Ni-Ti alloy, it was shown that maximum stress need not necessarily occur at the outer layer. On the basis of this observation, the Coffi n-Manson relation was modifi ed with parameters determined from this experiment. Results showed that the number of cycles to failure was infl uenced by the angle and radius of canal curvature and the size of instrument at the beginning of canal curvature. The resulting quantitative mathematical relation could be used to predict the lifespan of rotary Ni-Ti endodontic instruments under clinical conditions and thereby reduce the incidence of instrument failure in vivo.