Low Environmental Temperature Influences the Fatigue Resistance of Nickel-titanium Files

Effect of Temperatures on Cyclic Fatigue Resistance of 3 Different Ni-Ti Alloy Files

OBJECTIVE

The aim of this study was to investigate and compare the effect of temperature on the cyclic fatigue resistance of conventional (ProTaper Universal [PTU]), Gold-Wire (ProTaper Gold [PTG]), and Fire-Wire (EdgeTaper Platinum [ETP]) nickel-titanium alloy files.

METHOD

Twenty files from each system were tested for cyclic fatigue resistance in an artificial canal model. The experiments were performed at room temperature and body temperature in controlled temperature water. Magnified videos were recorded using a dental operating microscope integrated camera during testing to detect file fracture. The number of cycles to failure (NCF) was calculated. The type of failure was investigated macroscopically and microscopically with a dental operating microscope and scanning electron microscope, respectively.

RESULT

The NCF at room temperature was significantly higher compared with body temperature in each system (P < .001). Compared at the same temperature, the ETP group demonstrated the highest NCF, followed by the PTG and PTU groups (P < .001). All files demonstrated cyclic fatigue failure macroscopically and microscopically.

CONCLUSIONS

The 3 alloy files were affected by temperature. The cyclic fatigue resistance was reduced at the higher temperature and increased at the lower temperature. If the files are geometrically identical, files made of Fire-Wire are preferred compared with Gold-Wire and conventional nickel-titanium alloys based on cyclic fatigue resistance.

A novel model to evaluate the fatigue resistance of NiTi instruments: Rotational and axial movement at body temperature

To develop a model to test cyclic fatigue resistance of TruNatomy instruments undergoing rotational and axial movement at body temperature. A total of 288 Prime and Medium instruments were subjected to cyclic fatigue testing in simulated canals (at 37°C) using a model with either rotational movement only or rotational and axial movement simultaneously. Two different sized canals and three different types of curvatures were tested for each instrument (30/0.04 and 30/0.06 for Prime; 38/0.04 and 40/0.06 for Medium). The number of cycles to failure (fatigue resistance) was recorded. Rotational and axial movement of instruments led to greater fatigue resistance compared with rotational movement alone. Apical curvatures led to greater fatigue resistance than curvatures in the coronal and middle third. The developed dynamic model at body temperature to evaluate fatigue resistance of instrument closer simulates clinical scenarios.

Impact of cooling on shaping ability of thermally treated files in canal models with double curvature

Background

This study compared the ability of thermally treated files in shaping simulated canals with double curvature. Fifty-six canals were enlarged to a final size of 25 with ProTaper Next (PTN) or ZenFlex (ZF).

Materials

Half of the samples were shaped with cooled files (n = 14 each). The amount of removed resin was measured and canal deviation was determined at eight levels. Shaping time and maximum shaping torque values were also recorded. Data were statistically analyzed using analysis of variance and LSD, Kruskal-Wallis, and chi-square tests at a 0.05 significance level.

Results

Compared to PTN and cooled PTN, ZF and cooled ZF required lesser time to shape the canals. The maximum torques were found comparable between the groups. All the groups generated negligible deviations at every canal level evaluated and maintained the canal geometry. Although not significant, the cooled PTN and ZF files exhibited lesser canal deviations than their counterparts.

Conclusion

All groups demonstrated similar shaping ability whilst maintaining the original curvature of the canal in simulated canals with double curvature. However, ZF groups were able to shape the canals faster than PTN groups. There was a trend that cooled files made lesser canal deviations compared to their counterparts.

Cyclic Fatigue Resistance of Glide Path Rotary Files: A Systematic Review of in Vitro Studies

The aim of the present systematic review was to perform a qualitative synthesis of in vitro studies that assess the cyclic fatigue resistance of rotary glide path (GP) files of endodontic applications. Systematic electronic searches were performed in the Medline, Embase, Scopus, SciELO, and Web of Science databases on 15 February 2022, and were last updated on 1 April In vitro studies that evaluated and compared the cyclic fatigue resistance of at least one rotary GP file system with another rotary GP file system were included. A total of 25 studies were included in the qualitative synthesis. All studies assessing the difference in the cyclic fatigue resistance between continuous and reciprocating rotation in rotary glide path files found that the latter resulted in a significantly higher cyclic fatigue resistance, as evidenced by a higher number of cycles until fracture and/or time until fracture. Within the limitations of this review and the in vitro nature of the included studies, the results indicate that the cyclic fatigue resistance of rotary GP files may be influenced by several intrinsic factors of the files, such as their taper, cross-sectional design, alloy properties, kinematics, and external factors, such as the curvature and radius at which the file is activated, the irrigation or lubricant used, and the temperature.

Torsional, Static and Dynamic Cyclic Fatigue Resistance of Reciprocating and Continuous Rotating NiTi Instruments

INTRODUCTION

To evaluate torsional, dynamic and static cyclic fatigue resistance of the reciprocating One Reci (OR, Micromega, Besançon, France), WaveOne Gold (WOG, Dentsply Maillefer, Ballaigues, Switzerland), rotary One Curve (OC, MicroMega, Besançon, France) and ProTaper Next X2 (PTN X2, Dentsply Sirona, Ballaigues, Switzerland) instruments.

METHODS

A total of 120 NiTi instruments (n = 30) OR, WOG, OC and PTN X2 were used. Torque and rotation angle until failure under static torsion loading were measured according to the ISO 3630-1. Static and dynamic fatigue resistance was measured as the time to fracture (TTF) in an artificial stainless-steel canal with a 60° angle and 5-mm radius of curvature at intracanal temperature. The results were analyzed with one-way ANOVA and post-hoc Tukey tests. The alpha-type error was set at 5%. Fracture instruments from torsion and fatigue tests were examined with scanning electron microscope.

RESULTS

The OR showed higher static fatigue resistance and rotation angle at fracture than the WOG, OC and PTN X2 (P < .05). The WOG exhibited higher torsional resistance than the others (P < .05). Dynamic cyclic fatigue resistance tests had highest TTF than static for the PTN X2 and the WOG groups (P < .05). In the dynamic tests, the OR and WOG showed higher TTF than the OC and PTN X2 (P < .05).

CONCLUSIONS

Under these experimental condition, One Reci exhibited suitable mechanical properties with the highest cyclic fatigue resistance and angle of rotation among the tested instruments.

What meaningful information are the instruments mechanical testing giving us? A comprehensive review

Instruments mechanical strength and flexibility are traditionally tested by running cyclic fatigue, torsional, bending, buckling and microhardness tests. Several cyclic fatigue test models have been used in endodontics, all capable of providing a curved trajectory for the instrument to rotate. The cyclic fatigue testing allowed to identify conditions that may affect the fatigue strength outcomes, such as canal radius and degree of curvature, handpiece static vs dynamic motions, test temperature, kinematics, instrument previously wear and sterilization cycles, or instrument's size and metal alloy features. Due to the international test specifications for both torsional and bending tests, the variations of their models are not as many as for cyclic fatigue. These tests have also identified conditions capable of affecting the outcomes, such as kinematics, instrument's preloading, cross-sectional diameters, or alloy heat treatments. Buckling and microhardness are less common, with the metal alloy being considered to have a major influence on the results. Instruments mechanical testing, having all these individual conditions as independent variables, allowed to understand them and moulded the way the technical procedures are performed clinically. Even though the artificiality and simplicity of these tests will hardly mimic real working situations, and independently of being capable of producing cornerstone knowledge, these tests are also associated with inconsistency, lack of reproducibility and low external validity. Several attempts have been made to increase the generalizability of the outcomes by adding test settings that intend to mimic the clinical condition. Although pertinent, these settings may also add variabilities inherent to their concepts and practical applications in the laboratory environment. Although the actual studies should be seen as laboratory mechanical tests that measure very specific parameters under very particular conditions and that by far do not mimic the clinical condition, the lower validity drawback seems to be possible to be minimized when achieving a comprehensive understanding of the instrument behaviour. A Finite Elements Method and/or a multimethod research approach may lead to superior data collection, analysis, and results' interpretation, which when associated with a reliable confounding factors control and proper study designs may be helpful tools and strategies in order to increase the reliability of the outcomes.

Present status and future directions - Removal of fractured instruments

Success rate of fractured instrument retrieval varies because it is dependent mainly on several factors including the visibility of the fractured instrument, the length of the fractured instrument in relation to the curvature of the canal, and the techniques applied to each case. This review aims to update the present status on removal of fractured instruments to identify factors and variables that could affect the success of fractured instrument retrieval based on both the preparation techniques and the instrument retrieval techniques. On the other hand, future directions of fractured instrument retrieval should focus on management of non-visible fractured instruments since the removal of those instruments are deemed unpredictable with the current techniques, whereas the removal of visible fractured instruments are considered predictable now. Another possible direction of it is there might be no more instrument fracture due to possible significant changes in the root canal preparation technique which may dispense with the use of rotary instruments.

Effect of body temperature on the cyclic fatigue resistance of the nickel”titanium endodontic instruments: A systematic review and meta-analysis of in vitro studies

Aim:

The aim of this systematic review was to compare the effect of body temperature (I) on the cyclic fatigue resistance (O) of nickel–titanium (NiTi) endodontic instruments (P) to that of room temperature (C).

Methods:

The study was registered in the PROSPERO database (CRD42020204286). A systematic search in PubMed, Scopus, Web of Science, Google Scholar, and OpenGrey was conducted in English until December 31, 2021. In vitro studies comparing the cyclic fatigue resistance of NiTi instruments at the body (35°C ± 2°C) and room temperature (20°C–25°C) were included. Eligible studies were evaluated for risk of bias and meta-analyzed to estimate the effects.

Results:

Twenty-one studies out of 347 met the criteria for inclusion. The meta-analysis included six studies (n = 215) with comparative study parameters. The overall effect sizes (5.49; 95% confidence interval [CI]: 4.04–6.93) were significantly different (P < 0.001), indicating that the mean values at room temperature were significantly (P < 0.001) higher. The effect sizes for full rotary motion (standardized mean difference [SMD]: 4.80; 95% CI: 3.04–6.56) and reciprocating motion (SMD: 6.37; 95% CI: 3.63–9.11) were not significantly different (P = 0.346). Heterogeneity was high (I² = 94%). Sensitivity analysis revealed that the SMD values were not significantly different (P > 0.05) from the overall effect size, indicating that none of the studies had an effect on the overall effect size.

Conclusions:

Within the limitation of the study, the cyclic fatigue resistance of heat-treated NiTi endodontic files is significantly reduced at body temperature when compared to room temperature. Cyclic fatigue testing should be conducted at simulated body temperature.

A critical analysis of research methods and experimental models to study the physical properties of NiTi instruments and their fracture characteristics

The aim of this review is to provide a critical overview of the physical properties (surface hardness, cutting efficiency, bending properties, flexibility and cyclic fatigue resistance) of NiTi instruments. Frequently used experimental models regarding these aspects will be presented and discussed with regard to their strengths and weaknesses. For all these aspects, a plethora of experimental models have been described. Based on a critical appraisal and especially taking the appropriate translation of experimental findings to clinical endodontics into account, suggestions for future research based on clearly defined and valid experimental methodologies will be provided. Up to now, very few attempts have been made to assess which particular physical properties of NiTi instruments exert an impact on the clinical outcome of root canal treatment. Departure from merely focusing on physical properties and fracture characteristics towards more biological aspects in terms of treatment outcome is essential.

Heat Treatment and Surface Treatment of Nickel–Titanium Endodontic Instruments

Knowledge and thorough understanding of the characteristics of endodontic nickel–titanium (NiTi) files is paramount for dentists performing root canal treatments to patients. Understanding the behavior of the NiTi files guides the clinicians in choosing the correct instruments for different clinical and anatomical situations. This review focuses on the metallurgical properties of endodontic NiTi files, with a special emphasis on recent developments and improvements in metallurgy and the effects of heat treatment and surface treatment. In this study, the impact that such developments have on the properties of endodontic NiTi files is discussed.

Cyclic Fatigue Resistance of Blue Heat-Treated Instruments at Different Temperatures

The main aim is to evaluate the cyclic fatigue resistance of blue heat-treated instruments with different kinematics. Twenty-four endodontic instruments of the same brand were used for each of three experimental groups: VB (Vortex Blue 40/0.04), RB (RECIPROC Blue 40/0.06), and XB (X1 Blue 40/0.06). The instruments were randomly distributed and subjected to temperatures of 20°C and 37°C. The fatigue test was performed using a stainless steel device. Data were analysed using the Shapiro-Wilk test, Student's t-test, the F test, and Tukey's and Tamhane tests at significance level P=0.05. The instruments' cyclic fatigue resistance at both temperatures differed significantly for each instrument type (P < 0.001). The RB instruments displayed greater cyclic fatigue resistance at the tested temperatures compared with the VB and XB instruments (P < 0.001). Reciprocating kinematics positively influenced cyclic fatigue resistance. Blue heat-treated instruments showed decreased cyclic fatigue resistance as the temperature increased (P < 0.001).

Influence of surrounding temperature and angle of file access on cyclic fatigue resistance of two single file nickel-titanium instruments

The purpose of this study was to evaluate the influence of surrounding temperature and angle of file access on cyclic fatigue resistance of F6 SkyTaper (F6ST) and One Curve (OC). 120 new files #25.06 were tested at two insertion angles (0° and 20°) at room (20°C ± 1°C) and body (35°C ± 1°C) temperatures in a 16-mm stainless steel artificial canal (60° curvature and 5-mm radius), using a customised device. Cyclic fatigue resistance was expressed as time to fracture (TtF) in seconds. Data were analysed statistically (P < 0.05). All instruments exhibited lower TtF at 35°C (P < 0.05). An access of 20° did not significantly influence the TtF of tested instruments, independently from the temperature. OC exhibited higher TtF of F6ST at 20°C with a 20° inclination (P < 0.05). Under the present conditions, F6ST and OC showed a significant reduction of cyclic fatigue resistance at body temperature. A file inclined insertion did not affect the cyclic fatigue resistance of tested instruments at both temperatures.

Comparison of the effects from coronal pre-flaring and glide-path preparation on torque generation during root canal shaping procedure

This study aimed to evaluate the effect of glide-path preparation and coronal pre-flaring on torque generation of rotary nickel-titanium files. Sixty mesiobuccal root canals of 3D printed resin teeth (Dentalike) were randomly divided into 4 groups (n = 15) according to the preparation method; Group 1: OneCurve only; Group 2: OneG and OneCurve; Group 3: OneFlare and OneCurve; Group 4: OneFlare, OneG, and OneCurve. During the final canal preparation procedure, the torque generated was recorded. The sum of generated torque and maximum torque were calculated. Statistical analysis was performed with one-way ANOVA and Duncan's post hoc comparison. The summed torque was reduced by glide-path preparation and coronal pre-flaring (P < 0.05), whereas the maximum torque was not reduced by the glide-path preparation (P > 0.05). It will be advantageous to create a glide-path with coronal pre-flaring to reduce the stress and reactive forces to the NiTi file and root dentin.

In-Depth Metallurgical and Microstructural Analysis of Oneshape and Heat Treated Onecurve Instruments

OBJECTIVE

To define surface, mechanical, microstructural and metallurgical features of conventional One-Shape (OShape) and heat-treated OneCurve (OCurve) nickel-titanium instruments.

METHODS

Instruments were analysed by scanning electron microscopy (SEM) on new instruments and after simulated clinical use (SCU). Cyclic fatigue testing was performed and the number of cycles to fracture (NCF) and the length of the fractured instruments were measured (Mann-Whitney test). Fractured instruments during cyclic fatigue testing were then inspected by SEM fractographic analysis. Field emission gun scanning scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy were used to assess alloy surface chemistry. Focused ion beam (FIB) was performed to analyse the oxide layer on the surface of OCurve before and after SCU. X-Ray diffraction (XRD), metallographic evaluation and differential scanning calorimetry (DSC) were used to determine martensitic/austenitic phase transformation temperatures.

RESULTS

SEM observations on new instruments revealed a smooth regular surface with flattened milling grooves. No wear features were detected after SCU. OCurve exhibited a higher cyclic fatigue resistance (P<0.05), slower crack propagation and a surface layer of TiO2. Metallographic analysis and XRD showed the prevalence of martensitic grains on OCurve instruments that were stable at body temperature as confirmed by DSC analysis. Furthermore, DSC demonstrated a shift in the temperature transformation ranges suggesting an increase of martensite phase in autoclaved OCurve instruments.

CONCLUSION

Heat treatment processes were confirmed as a valid enhancement of the properties of the new generation NiTi instruments. OCurve presented a significant improvement over OShape regarding both mechanical and metallurgical characteristics.

Effects of Simultaneous Liquid or Gel Sodium Hypochlorite Irrigation on the Cyclic Fatigue of Two Single-File Nickel-Titanium Instruments

To evaluate the effect of simultaneous liquid or gel sodium hypochlorite (NaOCl) irrigation on cyclic fatigue of F6 SkyTaper (F6ST) and OneCurve (OC) single files, 180 new 25/0.06 F6ST and OC files were divided into 6 groups (n = 15) for each brand. Groups 1 and 4 included new instruments not exposed to NaOCl at 20 °C and 37 °C, respectively. Groups 2 and 5 included files activated with liquid NaOCl at 20 °C and 37 °C, respectively. Groups 3 and 6 consisted of instruments tested with NaOCl gel at 20 °C and 37 °C, respectively. Instruments were subjected to a fatigue test using a novel customized device. Data were expressed as time to fracture (TtF) and statistically analyzed (p < 0.05) after checking their normality through the Shapiro–Wilk test. Because they were normally distributed, 2-way analyses of variance (ANOVA) and the Tukey multiple comparison post-hoc test were used. Time to fracture of all tested instruments decreased at 37 °C (p < 0.05). At 20 °C, NaOCl improved TtF of F6ST and OC (p < 0.05). NaOCl liquid increased TtF of F6ST (p < 0.05) in comparison with gel, while there was no difference between the two formulations for OC. At 37 °C, both NaOCl formulations had no significant influence on TtF for F6ST, while they increased TtF of OC (p < 0.05). NaOCl improved the cyclic fatigue resistance of OC, independently of the temperature, while for F6ST the negative impact of higher temperature reduced the irrigant benefits.

Mechanical Properties and Metallurgical Features of New Green NiTi Reciprocating Instruments

To evaluate the properties of two nickel-titanium (NiTi) reciprocating endodontic instruments (commercially known as Procodile and Reziflow), a total of 40 size 25 and 0.06 taper new Procodile and Reziflow instruments (n = 20) were subjected to cyclic fatigue tests (60° angle of curvature, 5-mm radius) at 20 °C and 37 °C and a torsional test based on ISO 3630-1. The fracture surface of each fragment was examined. The morphological, mechanical, chemical, thermal, and phase composition characteristics of the files were investigated by field-emission gun scanning electron microscopy (FEG-SEM) equipped with an energy-dispersive X-ray (EDX) detector, focused ion beam analysis (FIB), micro-Raman spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Auger electron spectroscopy (AES). Reziflow showed higher cyclic fatigue resistance than Procodile at 37 °C (p < 0.05). The maximum torsional strength of Procodile was lower than that of Reziflow (p < 0.05). No difference was found between their angular rotations to fracture (p > 0.05). SEM, FIB, Micro-Raman, and AES analyses revealed the presence of an Nb/Nb2O5 coating on the Procodile surface. DSC and XRD analysis confirmed that both files consist of an almost austenitic phase structure at 37 °C. The cyclic fatigue resistance of Procodile and Reziflow significantly decreases upon exposure to body temperature.

Effect of Curvature Location on Fatigue Resistance of Five Nickel-titanium Files Determined at Body Temperature

INTRODUCTION

The purpose of this study was to evaluate the effect of 5 different curvature locations on the fatigue resistance of thermomechanically treated nickel-titanium (NiTi) files and superelastic NiTi files at body temperature and to document the corresponding phase transformations.

METHODS

EndoSequence (ES; Brasseler USA, Savannah, GA), EndoSequence CM (ESCM, Brasseler USA), K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and Vortex Blue (VB; Dentsply Tulsa Dental Specialties, Tulsa, OK) NiTi files (size 25/.04) were subjected to fatigue tests inside customized artificial canals containing a curvature of 60° and a 3-mm radius. There were 5 different canals based on the location of initial curvature; these included groups in which the distance between the canal orifice and the location of the curvature (DOC) was 5, 6, 8, 10, and 11 mm. The model canal was immersed in water at 37°C ± 1°C. The number of cycles to failure (N_f) was recorded, and the fracture surface of the fragments was examined by scanning electron microscopy. Two unused files of each brand were examined by differential scanning calorimetry.

RESULTS

The N_f was highest in the 10-mm and 11-mm DOC groups and lowest with the 5-mm and 6-mm DOC groups (P < .05). ESCM files had the highest fatigue resistance followed by the VB, K3XF, K3, and ES files (P < .05). ESCM files had the highest N_f (P < .05), and ES and K3 files had the lowest N_f (P < .05) depending on the curvature location. Two endothermic peaks were observed on the heating curve of the heat-treated files (ESCM, K3XF, and VB).

CONCLUSIONS

The location of the canal curvature had a significant effect on the fatigue resistance of both heat-treated and superelastic NiTi files. The fatigue life of files in the coronal curve was quite short.

Effect of canal curvature location on the cyclic fatigue resistance of reciprocating files

OBJECTIVES

To determine the effect of the location of the canal curvature on the fatigue resistance of WaveOne (WO), WaveOne Gold (WOG), Reciproc (Rec), and Reciproc Blue (RecB) files, and to examine the phase transformation behaviors of the reciprocating file systems.

MATERIAL AND METHODS

The instruments were subjected to fatigue testing in five artificial canals with a curvature of 60° angle and a 3-mm radius. The location of the curvature was unique for each canal. Each file was inserted 16 mm into the canal and operated until fracture occurred. The time to fracture was recorded and the length of the fragment was measured. Differential scanning calorimetry was used to characterize the thermal behavior of the files. The number of cycles to failure was analyzed using two-way analysis of variance and the post hoc Tukey test. The Kruskal-Wallis test was used to compare the mean fragment lengths between groups.

RESULTS

The instruments had significantly lower fatigue resistance in canals with curvatures in the middle and coronal canals compared with those with apical curvatures (p < 0.05). At all tested curvature locations, RecB had superior fatigue resistance compared with WO and Rec (p < 0.05). There were no significant differences between WOG and Rec in canals with curvatures in the middle and coronal canals. The DSC thermograms for RecB exhibit a single exothermic peak during cooling but double endothermic peaks during heating indicating that a two-step phase transformation from martensite to R-phase to austenite takes place.

CONCLUSIONS

The reciprocating instruments experience decreased cyclic fatigue resistance when operated in canals with coronal- and middle-third curvatures when compared with curvatures in the apical-third. Instrumenting coronally positioned curvatures with reciprocating files needs to be performed with caution.

CLINICAL RELEVANCE

The location of the root canal's curvature influences the fracture resistance of rotary files that are used with reciprocating movements. Therefore, caution needs to be exercised when using reciprocating instruments in canals with coronal or middle curvatures.

Influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium instruments: a systematic review

Objectives

This systematic review evaluated the influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) instruments.

Materials and Methods

A systematic search without restrictions was conducted in the following electronic databases: PubMed, Scopus, Web of Science, ScienceDirect, Cochrane, and Open Grey. The hand search was also performed in the main endodontic journals. The eligible studies were submitted to the methodological assessment and data extraction.

Results

From 203 abstracts, a total of 10 articles matched the eligible criteria. After reading the full articles, 2 were excluded because of the absence of the heat-treated instruments in the experimental design and 3 due to the lack of a control group using heat-treated instruments without autoclave sterilization. From the 5 included studies, 1 presented a low risk of bias, 3 presented moderate and 1 high risk. It was observed heterogeneous findings in the included studies, with autoclave sterilization cycles increasing, decreasing or not affecting the cyclic fatigue life of heat-treated NiTi instruments. However, the retrieved studies evaluating the cyclic fatigue resistance of endodontic instruments presented different protocols and assessing outcomes, this variability makes the findings less comparable within and also between groups and preclude the establishment of an unbiased scientific evidence base.

Conclusions

Considering the little scientific evidence and considerable risk of bias, it is still possible to conclude that autoclave sterilization procedures appear to influence the cyclic fatigue resistance of heat-treated NiTi instruments.

Fatigue resistance of ProTaper gold exposed to high-concentration sodium hypochlorite in double curvature artificial canal

This study aimed to evaluate and compare the fatigue resistance of ProTaper Gold (PTG) and ProTaper Universal (PTU) in artificial single and double curvature canals in 5% sodium hypochlorite (NaOCl) at body temperature (37 °C). PTG and PTU files (size F1) were subjected to fatigue tests in two different artificial ceramic canals. The single curvature model had a 60° curvature angle with a 5 mm radius. The double curvature model had a 60° curvature angle with a 5 mm radius and a second 30° curvature with a 2 mm radius. A file segment was introduced into the artificial canal and immersed in water or 5% NaOCl at 37 °C. The total number of cycles to fracture (NCF) was recorded. Data were analyzed using t-test and linear regression analysis. The NCF of all files was significantly influenced by the type of NiTi metal alloy (P < .01), canal curvatures (P < .01), and the environmental conditions (P < .05). PTG had higher fatigue resistance than PTU files in both single and double curvature canals (P < .05). The NCF of PTU files in 5% NaOCl was shorter than that in water (P < .05). The mean length of broken PTG was significantly shorter than those of PTU files in both single and double curvature canals (P < .01). The fatigue performance of PTG is better than that of PTU in both single and double curvature. Environmental conditions may affect the fatigue behavior of PTU files with single curvature.

A critical appraisal of studies on cyclic fatigue resistance of engine-driven endodontic instruments

The endodontic literature contains a plethora of studies on static and dynamic cyclic fatigue resistance tests performed on a large array of rotary or reciprocating nickel-titanium endodontic instruments. It was the aim of this review to summarize the currently available evidence to point out the different outcomes from static versus dynamic tests and to assess whether cyclic fatigue tests provide useful data and information for clinical practice. An electronic literature research in the database PubMed was performed using appropriate search terms, and the titles and abstract were screened for relevance. Language was restricted to English. The review reveals marked differences between the results obtained in static and dynamic tests, and also, the results for the same instruments assessed either under static or dynamic experimental conditions are widely inconsistent. Between the lowest and the highest value for one and the same pathfinding instrument was a factor of about 123 when cyclic fatigue was assessed either under static or dynamic experimental conditions. Moreover, standard deviations of up to 30% have been reported. Environmental temperature has a 500% impact on the lifetime of instruments. In conclusion, fatigue resistance tests conducted under room temperature should be regarded as having little meaning and the scientific and clinical benefits of fatigue resistance tests are very limited. These data should be provided by the manufacturer of the instruments.

Effect of Temperature of Sodium Hypochlorite on Cyclic Fatigue Resistance of Heat-treated Reciprocating Files

INTRODUCTION

The aim of this study was to evaluate the effect of different temperatures of sodium hypochlorite (NaOCl) on the cyclic fatigue resistance of the heat-treated file systems.

METHODS

The cyclic fatigue resistance of Reciproc 25 (VDW Dental, Munich, Germany), Reciproc Blue R25 (VDW), WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland), WaveOne Gold Primary (Dentsply Maillefer), and One Shape (25.06; Micro Mega, Besançon, France) was tested in the following conditions: control (no immersion), immersion in distilled water (DW) at 37°C ± 1°C, immersion in DW at 60°C ± 1°C, immersion in NaOCl at 37°C ± 1°C, and immersion in NaOCl at 60°C ± 1°C. The immersion period was 5 minutes for all conditions. A stainless steel artificial canal with a curvature of 60° and a 5-mm radius was used. The time to failure and fragment lengths were recorded for each instrument, and data were subjected to statistical analysis.

RESULTS

Reciproc Blue showed greater cyclic fatigue resistance in all conditions compared with the other systems (P < .05). Immersion in NaOCl at 60 °C negatively affected all instruments' cyclic fatigue resistance except Reciproc Blue. Immersion in DW at 60 °C increased the cyclic fatigue resistance of Reciproc Blue. Heat-treated files presented higher fatigue resistance than traditional files.

CONCLUSIONS

A high temperature of NaOCl affected the cyclic fatigue life of the file systems. Instruments produced with heat treatment presented a longer fatigue life.