Cyclic Fatigue Resistance of Nickel-Titanium Reciprocating Instruments after Simulated Clinical Use

Influence of the brushing motions on the dynamic cyclic fatigue resistance of the Reciproc Blue instrument: In vitro study

INTRODUCTION

This study aimed to evaluate the dynamic cyclic fatigue resistance of Reciproc® Blue files subjected to brushing motion.

METHODS

Twenty Reciproc® Blue files (R25, VDW, Munich, Germany) were employed for chemical-mechanical preparation in root canals of 3D printed replicas of mandibular molars. The instruments were divided into two groups (n=10): Group BM, instrumentation with brushing motions; Group WBM, instrumentation without brushing motions. Subsequently, the same instruments underwent cyclic fatigue testing using artificial canals consisting of a stainless-steel plate and an apical segment with a 45° curvature. Data regarding the time to fracture, number of cycles to fracture (NCF), and length of the fractured fragment were collected and subjected to statistical analysis using the t-test or Mann-Whitney test, with a significance level of 5%. Additionally, the fractured fragments were examined under a scanning electron microscope.

RESULTS

No statistical differences were observed between the groups in terms of time to fracture (p<0.05), NCF (p<0.05), and length of the fractured fragment (p<0.05).

CONCLUSION

The brushing motion did not affect the dynamic cyclic fatigue resistance of Reciproc Blue files.

Effects of Side Flattening on Torsional and Cyclic Fracture Resistance of Nickel-Titanium File

INTRODUCTION

The purpose of this study was to evaluate the effect of side flattening of cutting flutes on the cyclic resistance and torsional resistance of nickel-titanium files.

METHODS

Both novel flattened Platinum V.EU (PL) and standard nonflattened CC Premium V.EU (CC) rotaries were tested. For cyclic fatigue tests, all the files were rotated in an artificial root canal with a curvature of 45° and a radius of 6.06 mm at 300 rpm (n = 15 in each group). The number of cycles to failure (NCF) was calculated. For torsional tests, the files were rotated at 2 rpm clockwise until fracture occurred. The maximum torque value at fracture was measured and the toughness and distortion angle were computed. Subsequently, 5 fragments were randomly selected in each experiment, the cross-section and longitudinal direction of the fragments were photographed using a scanning electron microscope. An unpaired t-test was performed at a significance level of 95%.

RESULTS

There was a statistically significant difference in NCF between CC and PL (P < .05). CC showed higher NCF than PL. There was no statistically significant difference between CC and PL with regards to the parameters related to torsional resistance (distortion angle, ultimate strength, and toughness) (P > .05).

CONCLUSION

Within the limitations of this study, side flattening of the file did not improve cyclic resistance or torsional resistance of the files. As side flattening may reduce a file's cyclic resistance, such files should be used with caution in clinical practice.

Effect of simulated clinical use and sterilization on the cyclic fatigue resistance of nickel titanium files

Aim

Assess the effect of simulated clinical use and sterilization on the cyclic fatigue resistance of Race Evo and Tia Tornado Blue nickel titanium (NiTi) files.

Materials and Methods

For this study, a total of sixty-four NiTi files were selected, with thirty-two files each from two different manufacturers. Files from each manufacturer were subdivided into four subgroups (n = 8) based on the test parameters. The control groups included files that were neither used nor sterilized. Files from the test groups were used to prepare the root canals of extracted mandibular premolars and then sterilized. This procedure was repeated once, twice, or thrice, depending on the test group. All files were then subjected to a cyclic fatigue test. Data was statistically analyzed using the Kruskal-Wallis and Mann-Whitney U tests.

Results

No significant difference was observed in the number of cycles to failure (NCF) among the subgroups for both types of files (P = 0.869 for Tia Tornado Blue, P = 0.626 for Race Evo). Tia Tornado Blue files displayed significantly higher NCF values in the control (P = 0.021), once (P = 0.027), and thrice (P = 0.031) usage groups when compared to Race Evo files.

Conclusions

Repeated clinical use and sterilization for up to three cycles did not affect the cyclic fatigue resistance of Race Evo and Tia Tornado Blue files.

In Vitro Evaluation of the Dynamic Cyclic Fatigue Resistance of a New TruNatomy Glider File after Different Cycles of Use

INTRODUCTION

Determination of the glide path is recommended before using rotary instruments. This study aimed to evaluate the dynamic cyclic fatigue resistance of new and used glider rotary instruments in up to 6 root canals.

METHODS

Seventy-two TruNatomy Glider files were used for the preparation of root canals of extracted lower molars, which were then submitted to the dynamic cyclic fatigue test carried out in a curved metallic artificial canal. The instruments were divided into 4 groups (n = 18): Control group, new instruments without any use in the root canal; Group 2U, instruments used in 2 mesial canals; Group 4U, instruments used in 4 mesial canals; Group 6U, instruments used in 6 mesial canals. The time to failure (TF) of the instrument was recorded, and the number of cycles to failure (NCF) was calculated. The data were submitted to 1-way analysis of variance and to the Games-Howell test for multiple comparisons, adopting a significance level of 5%.

RESULTS

TF and NCF were significantly affected by the number of file uses. The Games-Howell test revealed that TF and NCF were significantly greater in the control group than in Group 4U. In Group 2U, TF and NCF were intermediate and not significantly different from the control group. Group 6U had significantly lower TF and NCF than all other groups.

CONCLUSION

The TruNatomy Glider can be used as a glide path for up to 2 mesial canals of mandibular molars, whereas its use on 4 or 6 root canals is not suggested.

Root Canal Instrumentation: Current Trends and Future Perspectives

The evolution of root canal instrumentation techniques has significantly impacted the field of endodontics, enhancing both the efficiency and outcomes of treatments. This review outlines the transition from manual to mechanical and rotary instruments, highlighting the role of nickel-titanium (NiTi) alloys and smart technologies in advancing procedural precision and reducing patient discomfort. Key historical developments and technological innovations, such as digital imaging and navigation systems, are explored for their contributions to improved clinical outcomes and patient satisfaction. Additionally, the review addresses the challenges presented by the complex anatomy of the root canal system and the advent of current instrumentation techniques. The potential of emerging trends, including artificial intelligence and advances in materials science, is discussed in the context of future endodontic practices. Despite the progress, challenges related to using advanced instrumentation methods, ethical considerations, and the cost factor of new technologies persist. The present review underscores the ongoing need for research and development to further refine root canal instrumentation techniques, ensuring that advancements in endodontic care remain patient-centered and accessible.

Cyclic and torsional fatigue resistance of a new rotary file on a rotary and reciprocating motion

This study evaluated the cyclic and torsional fatigue resistance of a new nickel-titanium (Flat File 25.04) instrument on the continuous and reciprocating motion. Sixty instruments of the ProDesign Logic2 25.03 and 25.05 (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil), and MK Flat File 25.04 (n = 20) (MK Life, Porto Alegre, Brazil) were used. For the cyclic fatigue test, an artificial stainless steel simulated canal with an angle of 60° and a radius of curvature of 5 mm located 5 mm from its tip was used. The torque and rotation angle at the instruments' failure on the torsional fatigue test was based on the ISO 3630-1 protocol, in which the 3 mm tip of each instrument was fixed and connected to an electric motor and a load cell. The fractured surface of each fragment was examined by scanning electron microscopy. Data were analyzed using a 1-way analysis of variance and Tukey's test with a significance level of 5%. Flat File 25.04 had lower cyclic fatigue in both kinematics than the Logic instruments (p < .05). Reciprocating motion improved the cyclic fatigue of the tested instruments (p < .05). Flat File 25.04 had similar torque to Logic2 25.05 (p > .05), and both were superior to Logic2 25.03 (p < .05). The angular deflection values were different for the three tested instruments (p < .05), in the decreasing order: Logic2 25.03, 25.05, and Flat File 25.04. Flat File presented good resistance to cyclic and torsional fatigue resistance. Reciprocating motion improved the cyclic fatigue resistance of the instruments and can be considered when using programmable motors. RESEARCH HIGHLIGHTS: Scanning electron microscopy evaluation of different endodontic rotary file and fatigue resistance tests.

Impact of access cavities on root canal preparation, restorative protocol quality, and fracture resistance of teeth

The survival of endodontically treated teeth depends on the remaining tooth structure. The aim of this study was to evaluate the impact of different access cavities on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth. Fifty-six mandibular molars were divided into control (n=8) and experimental (n=16) groups according to access cavity: Traditional, Conservative, and Truss; and redistributed (n=8) according to instrumentation protocols: Reciproc Blue and R-motion. After, teeth were scanned in micro-CT and then filled and redistributed according to composite resin restoration (n=8): Filtek One BulkFill and Filtek Z350. A new micro-CT scan was performed to analyze the restorative material. Then, samples were submitted to fracture resistance testing and the failure pattern was determined. Data were analyzed using paired T-test, ANOVA, Tukey, and chi-square tests (α=0.05). In Truss, R-Motion promoted less transportation in different thirds of root canals. Higher percentages of voids (5.05%) and filling material (11.7%) were observed in Truss. Fracture resistance values were higher for the control group, followed by Truss, Conservative, and Traditional. The predominant failure pattern was type-II. In Truss, reciprocating instruments with smaller taper showed less canal transportation. Also, Truss provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material. Thus, in Truss, reciprocating files with smaller taper showed less canal transportation, and these cavities provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material.

Evaluation of the rotary kinematics between actual and set speeds of X-Smart Plus, VDW.Silver and iRoot motors

The present study evaluated the actual rotational speed of three different endodontic motors compared to the values provided by the manufacturers. A total of three endodontic motors (X-Smart Plus, VDW.Silver, and iRoot) were tested at 400 rpm and 800 rpm and 2 N/cm2 torque. The kinematics of the devices was recorded by using a custom angle-measuring disc with a 50-mm diameter attached to the handpiece provided by the manufacturer, whereas their movement was captured by a high-speed camera at 2,400 frames per second, 800 x 800 pixel-resolution and distance of 0.3 m from the target object. Statistical analysis was performed at a significance level of 5%. At 400 rpm, the iRoot motor had a value of 17.94 rpm above that indicated by the manufacturer, which was significantly different from those of X-Smart Plus (5.20 rpm below that indicated by the manufacturer) and VDW.Silver (0.62 rpm above that indicated by the manufacturer) motors (P < 0.05). At 800 rpm, the iRoot motor had a value of 51.34 rpm below that indicated by the manufacturer, whereas the X-Smart Plus motor had a value of 13.00 rpm below that indicated by the manufacturer (P > 0.05). The VDW.Silver motor statistically differed from the iRoot and X-Smart Plus ones, showing a value of 1.68 rpm above that indicated by the manufacturer. In conclusion, the X-Smart Plus, VDW.Silver, and iRoot motors showed lower variations in the rotational speed values compared to those reported by their manufacturers. The endodontic motors presented different behaviors between them, with the VDW.Silver motor presents the most accurate values and the iRoot presents the most divergent values.

Effect of different axial speed patterns on cyclic fatigue resistance of rotary nickel-titanium instruments

BACKGROUND

To evaluate the effect of pecking motions with faster upward speed on the dynamic cyclic fatigue resistance of nickel-titanium rotary instruments with different metallurgy.

METHODS

Forty each of ProTaper Universal F3 (PTU) and ProTaper Gold F3 (PTG) instruments (size #30/.09) were equally divided into four groups. The test was performed using an 18-mm-long stainless steel artificial canal with a 5-mm radius of curvature, a 45° canal curvature and a 2-mm canal diameter. A downward speed of 100 mm/min was employed, while the upward speed was set at 100, 150, 200 or 300 mm/min. Time to failure (Tf), number of cycles to failure (Nf) and number of pecking motions to failure (Np) were recorded. Statistical analysis was performed using Kruskal Wallis and Mann-Whitney U tests for Tf, Nf, and Np (α = 0.05).

RESULTS

The 100/300 mm/min group showed significantly higher Np values than the 100/100 mm/min group (p < 0.05), whereas there were no significant differences in Tf and Nf among the tested speed groups (p < 0.05) in either PTU or PTG. PTG exhibited significantly higher Tf, Nf, and Np than PTU (p < 0.05).

CONCLUSIONS

Under the tested conditions, the fastest upward speed group showed significantly higher cyclic fatigue resistance, as demonstrated by larger Np, than the same speed group. PTG had significantly higher cyclic fatigue resistance than PTU in all groups.

Cyclic Fatigue Resistance of Nickel–Titanium Rotary Instruments after Simulated Clinical Use

Objective

Cyclic fatigue occurred in the curved canal when the instrument freely rotated leading to repeated compressive and tensile stresses. This study aims to evaluate the cyclic fatigue resistance (CFR) of new and used 2Shape and AF F-One rotary instrument systems by using an artificial stainless-steel canal.

Methods

A total of 80 rotary nickel–titanium (NiTi) instruments of two systems were used, 2Shape/TS2 and AF F-ONE/F5 (40 in each group). The instruments were subdivided into group A 20 instruments (10 per system) that remain unused, group B 20 instruments (10 per system) instrumented 20 root canals (each file prepared 1 canal for 2 minutes), group C 20 instruments (10 per system) instrumented 40 canals each for 2 minutes (each file prepared 2 canals), group D of 20 instruments (10 per system) prepared 60 canals each for 2 minutes (each file prepared 3 canals). After each canal instrumentation, the instruments were cleaned and sterilized by autoclave. Then, all the instruments underwent cyclic fatigue testing in an artificial stainless steel canal with a 50° canal curvature and a radius of curvature of 5 mm. The time and number of cycles to failure (NCF) were recorded. Data were analyzed using the Welch ANOVA test for intragroup comparison and the pairwise test for multiple comparisons.

Results

The unused instruments of the AF F-One rotary system showed statistically higher CFR than clinically used instruments (P < 0.05). 2Shape system was not affected by clinical use (P > 0.05). The mean NCF of AF F-One instruments was significantly higher than the equivalent file group of 2Shape instruments (P < 0.05).

Conclusion

A reduction in the CFR for AF F-One instruments after use was observed when compared to the new unused file group. The 2Shape system was not affected by clinical use. AF F-One performed better in terms of NCF.

A Computer-Assisted Approach to Assess the Precision of the Reciprocating Angles and the Rotation Speeds of Endodontic Motors

Endodontic reciprocating motors are largely used to support a series of procedures in dentistry treatments, useful for those different circular movement patterns. In the last years, different motors have been available on the market, with varying costs and promised performance for the users; however, since their reciprocating angles and rotation speeds may have significant outcomes on the employed endodontic files, there should be an affordable and practical way to assess the actual performance of such motors concerning their expected operation. Actually, endodontic files attached to reciprocating motors will move too fast to be easily accounted, which has fostered the development of computational methods to allow the proper validation of their movements according to their official datasheets. In this scenario, this paper describes a feasible method to detect the movement patterns of different reciprocating endodontic motors by the processing of a set of consecutive images taken by a high-speed camera. The performed experiments for three different off-the-shelf reciprocating endodontic motors showed that their actual movement characteristics are slightly different from their specifications, and that each considered motor has a particular movement pattern.

Surface roughness and cyclic fatigue resistance of reciprocating and novel rotary instruments after use in curved root canals

This study evaluated surface wear and resistance to fracture of reciprocating and novel rotary instruments after use in curved canals. Twenty new instruments (n = 5/each group): Reciproc Blue, WaveOne Gold, XP-endo Shaper (XPS) and TruNatomy were used twice for the instrumentation of simulated curved canals in plastic blocks. The instrumentation was performed according to the manufacturer's instructions at body temperature. Surface roughness was evaluated, using a profilometer, before instrumentation and twice after the instrumentation. Instruments were, then, subjected to a cyclic fatigue test to evaluate the time to failure. Differences were assessed using ANOVA and post hoc tests (α = 0.05). The XPS instruments showed significantly higher values of roughness compared with TruNatomy at every stage, especially after the second use (p < 0.008). Reciprocating instruments showed superior cyclic fatigue resistance compared with novel rotary instruments (p < 0.05). TruNatomy showed minimal surface roughness, and XPS exhibited significantly higher surface roughness.

Mechanical Properties of the New Generation RACE EVO and R-Motion Nickel-Titanium Instruments

This study aimed to evaluate and compare the dynamic cyclic fatigue, torsional and bending resistance of two novel RACE EVO (FKG Dentaire SA, La Chaux de Fonds, Switzerland) and R-Motion (FKG) nickel−titanium instruments with traditional RaCe (FKG) instruments. RACE EVO, R-Motion and RaCe instruments with a size of 25 and taper of 0.06 were used. A dynamic cyclic fatigue test was used to assess the time to fracture. The fractured surfaces were further analyzed using scanning electron microscopy at ×350 and ×3000 magnifications. A torsional resistance test was performed to measure the maximum torsional strength and angle of rotation. Phase transformations with temperature were evaluated using differential scanning calorimetry. The results were statistically analyzed with a Kruskal−Wallis test at a 5% significance level. R-Motion had the highest time to fracture and the lowest torsional and bending resistance, whereas RaCe had the lowest time to fracture and the highest torsional and bending resistance (p < 0.05). In relation to the angle of rotation, RACE EVO instruments had the highest deformation capacity followed by R-Motion and RaCe instruments (p < 0.05). The greater cyclic fatigue resistance and lower torsional and bending resistance results indicate that the novel R-Motion and RACE EVO instruments are less rigid and more flexible than RaCe instruments.

Cyclic fatigue and torsional resistance evaluation of Reciproc R25 instruments after simulated clinical use

BACKGROUND

To assess the influence of multiple uses on the cyclic flexural fatigue and torsional resistance of Reciproc R25 (REC) instruments.

METHODS

256 canals (2 for each mandibular molar) were prepared using Reciproc R25 instruments. A total of 96 25-mm-long Reciproc R25 instruments were divided in six groups (n=8) on the basis of different number of canal shaped: new instruments (control group), 1, 2, 3, 4 or 6 canals shaped during simulated clinical use for other groups respectively. Sixteen files were used for each of the six groups (8 instruments for cyclic fatigue test and 8 ones for torsional test). Times to fracture (TtF) for cyclic fatigue and ultimate torsional strength and angle of rotation to fracture for torsional resistance were recorded. Data were statistically evaluated by the analysis of variance (ANOVA) with P<.05.

RESULTS

As for cyclic fatigue resistance, there was no significant difference between new REC and REC used in one, two and three canals respectively (P>.05). REC used in four and six canals showed significant lower times to fracture when compared with other groups (P<.05) with REC used in six canals showing the significant lowest times to fracture (P<.05). Considering torsional resistance parameters, no significant difference was observed between the new and used instruments (P>.05).

CONCLUSIONS

REC25 files showed a significant decrease in cyclic fatigue resistance only when used in four or more molar canals while their torsional behavior was not affected by multiple uses.

Effect of number of uses and sterilization on the instrumented area and resistance of reciprocating instruments

Objectives

This study evaluated the effect of repeated uses and autoclaving in the instrumented area, fracture resistance, and time of instrumentation of thermally treated nickel-titanium reciprocating systems.

Materials and Methods

Two hundred simulated canals were instrumented using Reciproc Blue and WaveOne Gold. Each file was used up to 10 times or until fracture. The instrumented area was measured in pre- and post-operative images, using ImageJ software. Kaplan-Meier survival analysis evaluated the number of uses of instruments before fracture. Instrumented area and time of instrumentation were analyzed by Mann-Whitney U test and Kruskal-Wallis. Correlations among the number of uses and instrumented area were measured. The level of statistical significance was set at p < 0.05.

Results

Reciproc Blue presented a higher estimated number of uses in comparison with WaveOne Gold (p = 0.026), but autoclaving did not affect the resistance to fracture of instruments (p > 0.05). The instrumented area was different among the evaluated groups (p = 0.039), and the instrumented area along the uses of both tested instruments was reduced. With the time of instrumentation, there was also a significant difference among the evaluated groups; the groups without sterilization cycles were faster, in comparison to those submitted to autoclaving (p = 0.010).

Conclusions

Reciproc Blue was more resistant than WaveOne Gold, suffering later fracture. Additionally, the sterilization cycles did not influence the estimated number of uses of thermally treated reciprocating instruments, but the instrumented area of root canals was reduced along with the repeated uses of both instruments.

The Effect of Multiple Autoclave Sterilization on the Cyclic Fatigue of Three Heat-Treated Nickel-Titanium Rotary Files: EdgeFile X7, Vortex Blue, and TRUShape

OBJECTIVE

The purpose of this study was to evaluate the effect of repeated autoclave sterilization on the cyclic fatigue resistance of heat-treated NiTi rotary endodontic instruments.

MATERIALS AND METHODS

Three NiTi rotary endodontic instruments (EdgeFile X7, EFX7 0.30/0.4; Vortex Blue, VB 0.30/0.4; and TRUShape, TS 0.30/0.6) were selected. Each group (n = 24 each) was divided into 2 subgroups (n = 12 each): sterilized instruments and nonsterilized instruments. The sterilized instruments were subjected to 10 cycles of autoclave sterilization. Twelve instruments from each different subgroups were tested for cyclic fatigue resistance, and the number of cycles to failure (NCF) was calculated. Means and standard deviations were calculated for each group, and data were statistically analyzed using the SPSS program (P < 0.05).

RESULTS

Sterilized and nonsterilized EFX7 files showed the highest NCF compared with other file subgroups. Comparing the results between sterilized and nonsterilized instruments for each type of files, there was a statistically significant difference (P < 0.05) only between sterilized and nonsterilized EFX7 files (1198 versus 755 NCF). The other instruments did not show significant differences (P > 0.05) in the mean NCF as a result of sterilization cycles (VB, 606 versus 568 NCF; TS, 487 versus 442 NCF).

CONCLUSION

Repeated cycles of autoclave sterilization increased the NCF of the new heat-treated files, with EFX7 showing statistically significant superior results compared with other files tested.