Simulated Canals Research Articles

Cyclic Fatigue Resistance of Four Heat-Treated Nickel-Titanium Files in Severely Curved Simulated Canals: An In Vitro Study.

Background: Rotary Ni-Ti files are susceptible to sudden intra-canal separation due to cyclic fatigue stress, particularly in curved canals. To increase resistance to cyclic fatigue, new heat-treated files have been introduced. This study aimed to compare the performance of four heat-treated Ni-Ti files in two simulated curved root canals by evaluating the effect of the alloy, rotation speed, and diameter of the files on their resistance to cyclic fatigue. Methods: The Ni-Ti files included in the study were the ProTaper Gold® (Dentsply Sirona) F2, ProTaper Ultimate® (Dentsply Sirona) F2, FQ® (Komet) 25.06, and Blueshaper® (Zarc4Endo) Z4 25.06. Two groups of 30 files were selected for each system and were tested in two simulated canals milled in a specific metal template. One group was tested in a 60° curved canal and the other in a 90° curved canal. Results: In the 60° simulated canal, there were no instrument fractures within the 15 min time limit. In the 90° simulated canal, the Blueshaper Z4 demonstrated a lower resistance to cyclic fatigue, while FQ 25.06 showed statistically higher fatigue resistance based on both the Kruskal-Wallis and Games-Howell tests (p < 0.05). Conclusions: No differences were found between files when tested in a 60° curved canal for up to 15 min. However, in a 90° canal, the FQ® files showed significantly higher resistance to cyclic fatigue, especially compared to the Blueshaper® Z4. The ProTaper Ultimate and ProTaper Gold produced intermediate results, with the ProTaper Ultimate F2 slightly outperforming the ProTaper Gold F2.

The Effect of Canal Curvature and Different Manufacturing Processes of Five Different NiTi Rotary Files on Cyclic Fatigue Resistance

Abstract Objectives The aim of this study was to evaluate the cyclic fatigue resistance of ProTaper Universal, ProTaper Next, E-FLEX EDGE, E-FLEX ONE, and ZenFlex nickel-titanium (NiTi) rotary files in 60 and 90 degrees of simulated canal curvature. Materials and Methods ProTaper Universal, ProTaper Next, E-FLEX EDGE, E-FLEX ONE, and ZenFlex were used in this study. Each system was divided into two groups testing in simulated canals with 60 and 90 degrees of curvature. Both groups were set to rotate under a controlled temperature at 37°C until fracture. The number of cycles to fracture (NCF) was recorded and two fractured files from each group were randomly selected to analyze the fractographic pattern using scanning electron microscopy (SEM). Statistical Analysis The NCF between the two groups was analyzed statistically using the Mann–Whitney U test. The statistical differences between each system at the same degree of artificial canal curvature were analyzed using the Kruskal–Wallis test. A significant difference was set at p &lt; 0.05. Results E-FLEX ONE showed the highest mean NCF (p &lt; 0.05) when performed in 60- and 90-degree curvatures. In addition, the file tested in a 60-degree curvature exhibited higher resistance to cyclic fatigue than the one tested in a 90-degree curvature in the mutual NiTi system (p &lt; 0.05). The SEM micrographs exhibited a similar crack initiation area, which is the feature of cyclic fatigue failure. Conclusion E-FLEX ONE showed the greatest resistance to cyclic fatigue in both 60 and 90 degrees of curvature. This study implies that E-FLEX ONE is appropriate for severely curved canals.

Effectiveness of supplementary antimicrobial procedures in disinfecting lateral canals as evaluated by a novel ex vivo analytical approach

This ex vivo study devised an analytical ex vivo method for infection/disinfection of simulated lateral canals located in the middle and apical segments of the root. The antibacterial effects of supplementary approaches were tested in this model. Extracted mandibular premolars had their main root canals enlarged and then two lateral canals (100 μm in diameter) were created in the root, one in the apical and the other in the middle portion. Micro-computed tomography was used for specimen selection and to confirm the quality of the simulated ramifications. The specimens were contaminated with a mixed bacterial culture from subgingival bacterial biofilm added to pure Enterococcus faecalis strain ATCC 29212 grown overnight, using special strategies to facilitate culture medium penetration within the lateral canals. The following procedures were tested for disinfection: NaOCl/passive ultrasonic irrigation (PUI), NaOCl/XP-endo Finisher, ozonated water/continuous ultrasonic irrigation (CUI), and NaOCl/conventional irrigation with 30-G needles (control). Bacteriological samples were taken from the main canal before (S1) and after (S2) each supplementary protocol, and also from each lateral canal after treatment (S3). DNA extracted from the samples was subjected to quantitative real-time polymerase chain reaction. All S1 main canal samples were positive for bacterial presence. Bacterial counts in the main root canal substantially decreased by 99.2% after PUI, 99.1% after ozone/CUI, 99% after XP-endo Finisher, and 96% in the control group (P < 0.01 for all groups). There were no significant differences between groups (P > 0.05). The same was observed when comparing the effects of the supplementary approaches in the apical and middle lateral canals (P > 0.05). Only a few lateral canals showed no detectable bacteria. The method proposed here proved effective for ex vivo infection/disinfection studies. All supplementary approaches induced a substantial bacterial reduction in the main canal, with no significant differences between them. However, in terms of lateral canal disinfection, none of the tested approaches showed significant effects when compared to the control group.

Comparison of cyclic fatigue resistance of four pediatric rotary file systems at body temperature: an in vitro study

BackgroundThe aim of this study was to compare the cyclic fatigue resistance (CFR) of the newly developed pediatric nickel-titanium (NiTi) rotary file systems for root canal preparation of primary teeth.MethodsEighty pediatric NiTi rotary file systems files were used in this study, including 20 EasyInSmile X-Baby (25/0.04), 20 Scope miniScope (25/0.04), 20 EndoArt Pedo Gold (25/0.04), and 20 EndoArt Pedo Blue (25/0.04) files. Static CFR tests; performed on a custom-made stainless steel block with an inner diameter of 1.5 mm, an angle of curvature of 60° and a curved artificial canal with a radius of curvature of 5 mm. The test system was filled with distilled water and the temperature was kept constant at 35 ± 1 °C. The files were rotated in the simulated canal until fracture occurred. The number of cycles to failure (NCF) data was recorded, and all the fracture surfaces of the files were evaluated using scanning electron microscopy (SEM). One-way ANOVA and Tukey tests were used for statistical analysis of the data, and the significance level was set at p < 0.05.ResultsEndoArt Pedo Blue showed the highest NCF values (2668.10 ± 755.26), while the miniScope showed the lowest NCF values (453.65 ± 72.51), with a statistically significant difference between all the tested file systems (p < 0.05). There was no statistical difference in terms of fractured fragment lengths among all tested files (p > 0.05).ConclusionThe EndoArt Pedo Blue file system showed the best CFR performance among the four file systems specifically designed for primary teeth.

An in vitro comparative evaluation of cyclic fatigue resistance of two rotary and two reciprocating file systems.

Root canal instrumentation is one of the important procedures for successful endodontic therapy. Unexpected fracture of files occurs during root canal instrumentation without any visible signs of deformation compromising the success of root canal treatment. The aim of the study was to evaluate and compare cyclic fatigue resistance (CFR) of rotary and reciprocating files in simulated canals with 45°, 60°, and 90° angle of curvature. The study design was an In vitro study. Sixty nickel-titanium files, 30 each of rotary and reciprocating files were selected and divided into four groups (n = 15) of Neoendo Flex, ProTaper Next, WaveOne Gold (WOG), and Reciproc Blue (RPB) files. Each group was further subdivided into three subgroups containing five samples each based on their use in simulated canals with 45°, 60°, and 90° angle of curvature. To simulate root canals with 45°, 60°, and 90° angle of curvature, three artificial canals were designed in a stainless steel metal block. Each file was autoclaved, immersed in 3% sodium hypochlorite (NaOCl), and coated with 17% ethylenediaminetetraacetic acid (EDTA). Each file was tested for CFR using a torque-controlled reduction handpiece by instrumenting in a simulated canal for 10 s until fracture. The cycle of autoclaving, exposure to NaOCl, EDTA, and testing of CFR for 10 s per canal as per groups and subgroups was repeated again and again until the respective file fracture. The time taken to file fracture was recorded using a digital chronometer. The time taken for each file fracture (in minutes) was multiplied by the number of rotations per minute to attain the number of cycles to failure (NCF). The obtained results were subjected to statistical analysis using one-way analysis of variance and independent t-test. One-way ANOVA test showed a statistically significant difference between the four groups, P < 0.001. Independent "t"-test between individual subgroups showed a statistically significant difference, as P < 0.05. WOG and RPB reciprocating file systems showed superior CFR, more especially in canals with abrupt 90° angle of curvature compared to both rotary file systems tested. Among rotary file systems tested, Neoendo Flex showed greater CFR than ProTaper Next.

Influence of Autoclave Sterilization on the Resistance to Cyclic Fatigue of AF- F-ONE , ProTaper Ultimate, and ProTaper Gold NiTi Instruments (A Comparative Study)

Aims: This investigation aimed to examine the impact of autoclave sterilization on the cyclic fatigue of AF-F ONE, ProTaper Ultimate, and ProTaper Gold. Materials and Methods: Sixty #25 rotary files were categorized into groups as follows: AF-F ONE (Group A), ProTaper Ultimate (Group B), and ProTaper Gold (Group C). Additionally, within each group, there were subdivisions into sterilized and non-sterilized subgroups. Sterilized instruments underwent five cycles of sterilization by autoclave. Cyclic fatigue resistance was evaluated using a simulated canal featuring a single curvature (60° angle, 5-mm radius). Files were operated until fracture, and time and number of cycles to fracture (NCF) were recorded. Statistical analysis: One-way ANOVA, Post hoc Tukey test, and independent t-test. Results: ANOVA indicated a significant difference among non-sterilized groups (p &lt; 0.05). Tukey's test showing a notable difference between AF-F ONE and ProTaper Ultimate/ProTaper Gold (p &lt; 0.05), but not between the latter two (p&gt;0.05).AF-F ONE significantly decreased after autoclave sterilization (p &lt; 0.05), while ProTaper Ultimate and ProTaper Gold remained unaffected (p&gt;0.05). Conclusion: Autoclave sterilization significantly affected the cyclic fatigue of AF-F ONE, whereas ProTaper Ultimate and ProTaper Gold demonstrated resilience. Keywords: Cyclic fatigue, ProTaper Ultimate, AF-F ONE, autoclave sterilization.

Three-dimensional assessment of obturation volume in lateral canals after three obturation techniques with bioceramic sealer: an in vitro comparative study

ObjectiveThis study aimed to evaluate the obturation ability of simulated lateral canal in mandibular premolars at three levels (3, 5, and 7 mm) from the apex using gutta-percha and BC Sealer HiFlow (BCHiF) with different obturation techniques, including continuous wave compaction (CWC), cold lateral condensation (CLC), and single cone (SC) techniques, by a 3D assessment method of the obturation volume with cone beam computed tomography (CBCT) and MIMICS software analysis.MethodsThirty intact human mandibular premolars were decoronated, instrumented up to #30 taper 4%, and uniformly irrigated with 5.25% NaOCl and 17% EDTA. Six simulated lateral canals (3 pairs) were prepared at 3, 5, and 7 mm from the apex in each root, using #10 modified C-file. CBCT images were obtained, and lateral canal volumes were calculated using MIMICS software. The samples were divided into three groups: CWC (n = 10), CLC (n = 10), and SC (n = 10). All groups were obturated with BCHiF and gutta-percha. Another CBCT image was taken post-obturation, and 3D lateral canal obturation volume percentages were calculated using MIMICS software. Data were analyzed using SPSS software with One-way ANOVA and Sidak tests (α = 0.05).ResultsSignificant differences were observed in the 3D lateral canal obturation volume percentage at all three levels (P < 0.05). Both CWC and CLC techniques demonstrated higher 3D lateral canal obturation volume percentages (x¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{x}$$\\end{document} = 89.64% and x¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{x}$$\\end{document} = 73.28%; respectively) compared to the SC group) x¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{x}$$\\end{document} = 43.10%).ConclusionBCHiF combined with the CWC technique has a higher ability to achieve preferable 3D obturation volume in the simulated lateral canal at 3, 5, and 7 mm.Clinical relevanceIn cases requiring endodontic treatment with lateral canals, the CWC obturation technique using BCHiF with gutta-percha may offer better outcomes compared to other obturation techniques.

Students’ perceptions of endodontic typodont teeth with simulated canals printed from novel materials

Students’ perceptions of endodontic typodont teeth with simulated canals printed from novel materials

Dynamic Photoelastic Analysis of Stress Distribution in Simulated Canals Using Rotary Instruments with Varied Tip and Taper Sizes: A Quasi-3D Approach

IntroductionTo compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. MethodsNinety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n = 5) based on the instrument tip (sizes 10, 15, 20, 25, 30, and 35) and taper (sizes 0.02, 0.04, and 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen's Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal–Wallis test followed by an all-pairwise posthoc procedure (α = 5%). ResultsInter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P = .011), middle (P = .006), and apical (P = .026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P = .509), middle (P = .958), or apical (P = .493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P = .181). ConclusionsThe stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared to the canal thirds.

Assessment of the Cyclic Fatigue Performance of the Novel Protaper Ultimate File System Used in Different Kinematics: An In Vitro Study.

This in vitro study aims to assess the cyclic fatigue resistance of the Protaper Ultimate (PTU) files compared to the Protaper Gold (PTG) and the M3 UDG (M3) files using various motion kinematics in simulated canals. As far as the authors are aware, no study has previously compared the three file systems before this current investigation. Therefore, closing this information gap is the goal of the current research. Methods: A total of (60 new endodontic files were randomly divided into 6 groups (10 files per group); groups 1, 3, and 5 used continuous rotation (CR), while groups 2, 4, and 6 used forward reciprocating motion (FRM). A manufactured stainless-steel artificial canal was used to perform the cyclic fatigue testing. The results were analyzed using Student's t-test and two-way ANOVA. All pairwise comparisons revealed statistically significant differences in the time to failure (TTF) for every study group (p < 0.001), with the exception of the PTG and M3 files, which performed similarly using both CR and FRM. Conclusions: The PTU files performed better than the PTG and M3 files in terms of the TTF and number of cycles to failure (NCF) using both CR and FRM.

Multimethod analysis of large- and low-tapered single file reciprocating instruments: Design, metallurgy, mechanical performance, and irrigation flow.

To compare eight large- and low-tapered heat-treated reciprocating instruments regarding their design, metallurgy, mechanical properties, and irrigation flow through an in silico model. A total of 472 new 25-mm E-Flex Rex (25/.04 and 25/.06), Excalibur (25/.05), Procodile (25/.06), Reciproc Blue R25 (25/.08v), WaveOne Gold Primary (25/.07v), and Univy Sense (25/.04 and 25/.06) instruments were evaluated regarding their design (stereomicroscopy, scanning electron microscopy, and 3D surface scanning), metallurgy (energy-dispersive X-ray spectroscopy and differential scanning calorimetry), and mechanical performance (cyclic fatigue, torsional resistance, cutting ability, bending and buckling resistance). Computational fluid dynamics assessment was also conducted to determine the irrigation flow pattern, apical pressure, and wall shear stress in simulated canal preparations. Kruskal-Wallis and one-way anova post hoc Tukey tests were used for statistical comparisons (α = 5%). Instruments presented variations in blade numbers, helical angles, and tip designs, with all featuring non-active tips, symmetrical blades, and equiatomic nickel-titanium ratios. Cross-sectional designs exhibited an S-shaped geometry, except for WaveOne Gold. Univy 25/.04 and Reciproc Blue displayed the smallest and largest core diameters at D3. Univy 25/.04 and E-Flex Rec 25/.04 demonstrated the longest time to fracture (p < .05). Reciproc Blue and Univy 25/.04 exhibited the highest and lowest torque to fracture, respectively (p < .05). Univy 25/.04 and Reciproc Blue had the highest rotation angles, whilst E-Flex Rec 25/.06 showed the lowest angle (p < .05). The better cutting ability was observed with E-Flex Rec 25/.06, Procodile, Excalibur, and Reciproc Blue (p > .05). Reciproc R25 and E-Flex Rec showed the highest buckling resistance values (p < .05), with WaveOne Gold being the least flexible instrument. The impact of instruments' size and taper on wall shear stress and apical pressure did not follow a distinct pattern, although Univy 25/.04 and E-Flex Rec 25/.06 yielded the highest and lowest values for both parameters, respectively. Low-tapered reciprocating instruments exhibit increased flexibility, higher time to fracture, and greater angles of rotation, coupled with reduced maximum bending loads and buckling strength compared to large-tapered instruments. Nevertheless, low-tapered systems also exhibit lower maximum torque to fracture and inferior cutting ability, contributing to a narrower apical canal enlargement that may compromise the penetration of irrigants in that region.

Effect of MT Technology of Heat Treatment on Reciproc: Comparison of Reciproc, Reciproc Blue, and Reciproc MT

IntroductionThis study aimed to evaluate the effects from the memory-triple (MT) heat treatment on the fatigue resistance of the Reciproc by comparison with the file systems of same geometry. MethodsReciproc files subjected to MT heat treatment technology were designated as Group RMT and were compared with the original Reciproc (Group REC) and Reciproc Blue (Group REB). Each NiTi file from 3 groups (n = 15) was operated reciprocally with a repetitive up-and-down movement in the curved canal with 4 mm of pecking distance inside of the simulated canal at body temperature. When each file fractured, the time until fracture was recorded. The length of the fractured fragment was measured. Fractured fragments were observed under scanning electron microscope (SEM) to evaluate the topographic features of the surface. Differential scanning calorimetry (DSC) analysis was performed to estimate phase transformation temperatures. One-way analysis of variance and Duncan post hoc comparison were applied to compare among the groups at a significance level of 95%. ResultsRMT showed significantly higher fracture resistance (P < .05), whereas there was no difference in fatigue resistance between REC and REB. SEM examination showed the files from the 3 groups had similar topographic features. RMT showed a peak of austenite peak (Ap) at a temperature (52°C) higher than body temperature, whereas REC and REB showed Ap at 37 and 32°C, respectively. ConclusionsUnder the condition of this study, the new heat treatment technique of MT technology could enhance the fatigue fracture resistance of the reciprocating files made of M-wire and Blue-wire.

The effect of rotational speed on force and torque during instrumentation of simulated root canals using ProTaper Next rotary files

Introduction: Rotary nickel–titanium files are subjected to shear and flexural stresses during instrumentation. Increasing the rotational speed may reduce the shear stresses but can deteriorate the fatigue life of the file. This in vitro study aimed to address the influence of three rotational speeds 300, 500, and 700 RPM on the apical force and torque generated during instrumentation as well as on file fracture. Materials and Methods: A total of 48 simulated canals were divided into three groups: 300, 500, and 700 RPM (n = 16). Each canal was instrumented using a ProTaper Next XA orifice opener to prepare the coronal third and an X2 shaper to prepare the middle and apical thirds. A new set of files (XA and X2) was used to prepare four canals. A customized setup was used to evaluate the maximum apical force and torque corresponding to each third of the canal. The files were inspected for deformation or fracture using a stereomicroscope. Force and torque data were analyzed using analysis of variance and Post hoc Tukey test at 5% significance. Results: Five hundred and 700 RPM generated a significantly lower apical force and torque than 300 RPM at all canal thirds (P &lt; 0.001). However, 700 RPM was superior to 500 RPM at the coronal third only (P &lt; 0.001). No incidence of deformation or fracture was reported in any group. Conclusions: In resin artificial canals, increasing the rotational speed of the tested ProTaper Next files resulted in significantly less apical force and torque without increasing the incidence of fracture. Further studies involving natural teeth are required to validate these results using natural teeth.

Cyclic fatigue resistance of ProTaper gold and two replicalike rotary systems. An in vitro study

Introduction: As a new phenomenon in endodontics, it was observed that nickel–titanium (NiTi) rotary systems closely replicate the systems created by the original companies are manufactured and available in the market for clinicians. These replica systems are usually sold at lower prices than the original rotary systems, which attracted end-user clinicians. Although clinicians widely use these replica systems, their mechanical performance has not been evaluated in any scientific literature. The aim of the current study was to analyze the cyclic fatigue resistance of two lower prices replica NiTi rotary file systems involving 0.25/0.08 v of MG3 Gold Perfect® and V TAPER Gold Fanta versus ProTaper Gold®. Materials and Methods: The NiTi rotary instruments (n = 15 of each) were allowed to rotate continuously, in dynamic mode, in a simulated stainless steel canal having a 6 mm radius and 60° curve till fracture. Time to fracture (TTF) in seconds was recorded, and the number of cycles to failure (NCF) was calculated. TTF and NCF were compared between the three groups. Results: The V TAPER Gold Fanta instrument showed significantly longer TTF than the ProTaper Gold instrument (mean = 1130.30 ± 244.42 vs. 354.30 ± 52.01 s), accounting for a three-fold difference in NCF (mean = 6593.42 ± 1425.79 vs. 2066.75 ± 303.40 cycles, P &lt; 0.001). However, an insignificant difference in TTF was observed between the MG3 Gold Perfect® and ProTaper Gold instruments (P = 1.00). Conclusions: The V TAPER Gold Fanta instrument is a safe and cost-effective alternative to the ProTaper Gold instrument.

Impact of Angle of File Access and Location of Canal Curvature on the Dynamic Cyclic Fatigue of Nickel Titanium Rotary Instruments.

To evaluate the impact of different file access angles and root canal curvature's location on the fatigue failure of One Curve (OC) and E3 Azure (EZ) NiTi files using a dynamic model at simulated body temperature. Eighty new instruments with similar tip sizes and taper (#25/0.06) from two NiTi rotary systems, One Curve and E3 Azure, were tested at simulated body temperatures (37°C) using a custom-made dynamic cyclic fatigue device. Instruments were divided into four subgroups according to the location of root canal curvature (a coronal curve 5 mm from the root canal orifice and an apical curve 10 mm from the root canal orifice) and the angle of file access (0° or 30°). Instruments were operated in simulated stainless-steel canals having a 60° curve and a 3 mm radius. A custom-made device produced controlled vertical pecks during file rotation. Time to failure (sec) was registered, and the length of the fragment segments was measured (mm). Data were analysed statistically with One-Way ANOVA and Tukey post hoc tests. The significance level was set at 5%. All separated instruments were examined by scanning electron microscope. One-way ANOVA (p<0.05) found a significant difference among the tested instruments. Post Hoc analysis revealed lower cyclic fatigue resistance when the angle of file access was 30º, and the root canal curvature was located coronally for both files (p<0.0001). Three-way ANOVA showed that the angle of file access was the most influential contributor to cyclic fatigue, followed by the location of file curvature and, finally, the file type (p<0.0001). The fractographic examination revealed a predominantly ductile fracture mode for all tested instruments. The lengths of all fractured segments showed no significant difference (p>0.05), indicating an accurate trajectory during testing. OC files had superior cyclic fatigue resistance than EZ files; coronal curvatures negatively impacted cyclic fatigue resistance compared to apical curvatures, while the angle of file access presented the highest impact on dynamic cyclic fatigue.

Assessment of the Effect of Different Irrigation Protocols on the Penetration of Irrigation Solution into Simulated Lateral Canals (In Vitro Study).

To compare the effectiveness of lateral canal irrigation penetration by conventional needle, passive ultrasonic, sonic endo activator, and Erbium laser (2780nm). A total of 40 palatal roots of human maxillary first molars were collected and instrumented at a working length of 12 mm by an X1-X4 rotary Protaper Next system (Dentsply, Maillefer, Ballaigues, Switzerland) using the crown-down technique. Artificial lateral canals were made at 2, 4, and 6 mm from the apex on mesial and distal sides using an ISO rotary reamer (Dentsply, Maillefer, Ballaigues, Switzerland; #10 for mesial, #08 for distal). The samples were then cleared using methyl salicylate. A solution of black ink and normal saline was used as an irrigant for the root canal. The percentages of the penetration of the ink into the lateral canals were measured using a stereomicroscope (Q-Scope, Arnhem, The Netherlands) with the aid of program Image J. The Tukey test is used to assess the significant difference between intragroup and intergroup comparisons of different thirds, and the T-test is used to assess the significant difference between every two groups and for the mesial and distal sides of each group. The level of significance was set at 0.05. Results showed that none of the activation techniques used resulted in complete lateral canal penetrations; however, on both sides at all thirds, the Erbium laser (2780 nm) achieved the highest results with a highly significant statistical difference (p=0.05) with all other groups, and the least penetration was in the conventional needle group. The size of the lateral canal is a restricting factor for all activation methods; the best results can be achieved by laser. Conventional needles cannot be used alone to disinfect complex canal anatomy; however, passive ultrasonic and sonic endo activator activations can produce comparable results.

Precision-milled simulated curved root canals in bovine dentine for the assessment of chemo-mechanical root canal preparation.

The aim was to develop a standardized curved root canal model in bovine dentine and to assess whether that natural substrate would behave differently from the resin in standard plastic training blocks when prepared chemo-mechanically. The impact of substrate microhardness on simulated canal transportation was considered. High-precision computer numerical control (CNC) milling was used to recreate a simulated root canal from a resin training block (Endo Training Bloc J-Shape, size 15) in longitudinally sectioned, dis- and re-assembled bovine incisor roots. Optical overlays obtained from 10 resin blocks were used to identify an average canal and program the CNC milling apparatus accordingly. Resin and dentine microhardness were measured. Simulated root canals in resin training blocks and their bovine counterparts were then instrumented at 37°C using Reciproc R25 instruments (VDW) with water or 17% EDTA (n = 10). Open-access image processing software was used to superimpose and analyse pre- and postoperative images obtained with a digital microscope. Centering ratios were averaged to indicate canal transportation. The effects of substrate and irrigant on canal transportation were assessed by two-way anova. Superimposed images showed that resin blocks under investigation varied considerably in terms of simulated canal length and curvature, whilst the milled canals were highly similar. The microhardness of dentine was more than three times higher than that of the resin. Conversely, canal transportation was considerably greater in dentine compared to resin, and in dentine had a tendency to be increased by EDTA. There was a strong effect of substrate on canal transportation (p < .001), no overall effect of irrigant, and a marginally significant interaction between irrigant and substrate (p = .077). CNC milling allows to create standardized simulated curved root canals in bovine dentine. These models may be useful to test and compare materials and concepts of chemo-mechanical root canal instrumentation. Microhardness is a bulk feature that does not predict the response to chemo-mechanical instrumentation of a composite material such as dentine.

Influence of sodium hypochlorite on cyclic fatigue resistance of nickel-titanium instruments: A systematic review and meta-analysis of in vitro studies.

This systematic review/meta-analysis investigated the influence of NaOCl on cyclic fatigue resistance of endodontic NiTi instruments. A systematic search until July 2022 in PubMed/MEDLINE, Embase, Scopus, Web of Science, SciELO, Cochrane Library, and grey literature was conducted. According to the PECOS strategy, only in vitro studies evaluating the effects of NaOCl on the cyclic fatigue resistance of NiTi instruments were eligible. Cyclic fatigue resistance was the primary outcome. A modified Joanna Briggs Institute's Checklist was used for risk of bias assessment. Of the 2,445 records screened, 37 studies were included. Most studies used simulated canals made of stainless-steel block with severe to moderate curvatures. NaOCl concentration varied from 1-6%, mainly at 37°C. Regarding fatigue resistance, 23 studies using 1.2% to 6% NaOCl showed a reduction in the resistance compared to the control groups, especially when pre-heated. Four meta-analyses were performed according to the tested NiTi systems. The meta-analyses indicated that the PTU F2 files had higher reduction of fatigue resistance after exposure to 5.25% NaOCl; no differences between NaOCl and no immersion were observed for Reciproc R25, WaveOne 25.08, and WaveOne Gold Primary files. Included studies had low risk of bias. NaOCl appears to reduce cyclic fatigue resistance of certain NiTi files, especially when they are pre-heated, particularly in conventional NiTi files compared to some heat-treated instruments. It is possible that the temperature of the solution may have a greater influence on resistance than NaOCl itself. Important to note that an overall tendency toward no significant influence was observed among various systems. Precautions are necessary when a pre-heated high-concentration NaOCl is used to enhance its properties during root canal preparation, mainly using conventional wire.

Characterization of four heat-treated reciprocating instruments: Design, metallurgy, mechanical performance, and irrigation flow patterns.

To compare the design, metallurgy, and mechanical properties of four heat-treated reciprocating instruments coupled with the evaluation of the irrigation flow using an in silico model. New EdgeOne Fire Primary, Easy-File Flex Regular 25, WaveOne Gold Primary and Reciproc Blue R25 instruments (n = 124) were initially evaluated regarding their design through stereomicroscopy, scanning electron microscopy and 3D surface scanning. In addition, energy-dispersive X-ray spectroscopy was utilized to determine their elemental composition, and differential scanning calorimetry tests to evaluate their phase transformation temperatures. Their mechanical performance was further assessed through torsional and bending tests. Using scans obtained from a real tooth and the instruments, a computational fluid dynamics assessment was conducted to determine the irrigation flow pattern, apical pressure, and wall shear stress in simulated canal preparation. Mood's median and One-way anova post hoc Tukey tests were used for statistical comparisons (α = 5%). Reciproc Blue exhibited a superior number of blades (n = 8), whereas EdgeOne Fire had the highest overall volume (4.38 mm3 ) and surface area (32.32 mm2 ). At the 3-mm axial level, EdgeOne Fire displayed the lowest core diameter (0.13 mm), while Reciproc Blue had the highest (0.16 mm). All blades were symmetrical, and the tips of the instruments were non-active but differed from each other. The most irregular surfaces were observed in EdgeOne Fire and Easy-File Flex. All instruments were manufactured from nickel-titanium alloys and exhibited distinct phase transformation temperatures. WaveOne Gold and Reciproc Blue demonstrated the highest maximum torque values (1.87 and 1.62 N cm, respectively), while the lowest was observed on EdgeOne Fire (1.21 N cm) (p < .05). The most flexible (p < .05) were EdgeOne Fire (angle of rotation: 602.6°; maximum bending load: 251.4 g.f) and Reciproc Blue (533.2° and 235.6 g.f). There were no significant differences observed in the irrigation flow among the four domains generated by the tested instruments. Despite observing variations in the design, phase transformation temperatures, and in the torsional and bending test outcomes among the four heat-treated reciprocating instruments, no significant differences were found in the irrigation flow pattern among the different groups in the simulated root canal preparations.

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.