New thermomechanically treated NiTi alloys - a review

Effect of several nickel-titanium rotary systems on stress distribution in mandibular molars under occlusal forces: a finite element analysis

This study assessed the stress distribution under occlusal forces in mandibular molars after utilizing several nickel-titanium rotary systems and identified potential root fracture patterns through finite element analysis (FEA). Five three-dimensionally printed mandibular molars were used, with one tooth left unshaped and the remaining four shaped using ProTaper Gold (Dentsply, Tulsa Dental Specialties, Tulsa, OK), Reciproc Blue (VDW, Munich, Germany), XP-endo Shaper (FKG Dentaire, La Chaux-de-Fonds, Switzerland), and Hyflex EDM (Coltene/Whaledent, Altst€atten, Switzerland) rotary systems. Subsequently, micro-CT scans were performed on the teeth, and representative FEA models were generated. Two distinct loadings, vertical and oblique, were applied, and stress parameters including von Mises stress, maximum principal stress, and minimum principal stress were recorded and compared across groups. Although stress values in both loading conditions correlated with volume increases post-shaping, the stress distribution patterns indicative of potential fractures were comparable across groups. Stresses under oblique loads were observed to be higher than those under vertical loads. Several rotary systems, based on the volumetric changes they induce in dental hard tissues, may elevate stress values throughout the tooth, leading to root fractures in regions where stress concentration occurs. Conservative root canal shaping leads to a lower overall stress concentration. In mandibular molars, oblique forces have a more destructive effect compared to vertical forces.

Exploring morphometric transformations in temperature-sensitive NiTi instruments alongside real-time intracanal temperature dynamics

AIM

This study was twofold: (i) it aimed to investigate the morphometric changes of three temperature-sensitive nickel-titanium (NiTi) instruments at different temperatures, and (ii) to conduct an in vivo real-time analysis of intracanal temperature changes.

METHODS

Changes in the shape and length of XP-Endo Shaper, XP-Endo Finisher, and XP-Endo Finisher-R were evaluated in real time whilst heated in a temperature-controlled water bath from 22 to 45°C. Instruments were fixed to a laminated water-resistant 1 mm graph paper attached to a stone block. Instruments were imaged whilst subjected to increasing temperature using a digital camera attached to an operating microscope. From recorded videos, still frames were extracted at 10-s intervals and changes in the length and shape of each instrument were measured and changes were plotted against time. Moreover, the intracanal temperature of distal roots of lower molars was measured in vivo for patients attending the clinic for non-surgical root canal treatments. The temperature was measured using a K-type thermocouple probe inserted into the mid-root level after irrigating the canal with a solution set at room temperature (22°C) or heated to 45°C. The intraoral and intracanal temperatures were recorded using a video camera for 180 s at 5-s intervals to plot the change in the intraoral and intracanal temperature, after both irrigation solution temperatures, with time.

RESULTS

The shape transformation of XP-Endo Shaper began at 31.5 ± 2.0°C and reached its optimal transformation at 35.1 ± 1.0°C. For the Finisher and Finisher-R, shape transformations began at 29.2 ± 1.9 and 26.9 ± 2.2°C reaching the optimal transformation at 33.9 ± 1.4 and 32.7 ± 1.7°C, respectively. The average decreases in lengths of XP-Endo Shaper, Finisher, and Finisher-R after full transformation were 0.43 ± 0.23, 1.07 ± 0.22, and 1.15 ± 0.22 mm, respectively. The intracanal temperature reached 32.9 ± 0.8 and 33.2 ± 1.0°C after 3 min of application of irrigation solutions set at 22 or 45°C, respectively.

CONCLUSION

The tested instruments exhibited diverse changes in their shapes and lengths at varying temperatures. Despite the temperature of the irrigation solution, the intracanal temperature consistently remained lower than the intracanal temperature once equilibrium was reached. This highlights the importance of considering the temperature of irrigation solution during in vitro testing of endodontic instruments.

Effect of repetitive up-and-down movements on torque/force generation, surface defects and shaping ability of nickel-titanium rotary instruments: an ex vivo study

BACKGROUND

The screw-in effect is a tendency of a nickel-titanium (NiTi) rotary endodontic file to be pulled into the canal, which can result in a sudden increase in stress leading to instrument fracture, and over-instrumentation beyond the apex. To reduce screw-in force, repeated up-and-down movements are recommended to distribute flexural stress during instrumentation, especially in curved and constricted canals. However, there is no consensus on the optimal number of repetitions. Therefore, this study aimed to examine how repeated up-and-down movements at the working length affect torque/force generation, surface defects, and canal shaping ability of JIZAI and TruNatomy instruments.

METHODS

An original automated root canal instrumentation device was used to prepare canals and to record torque/force changes. The mesial roots of human mandibular molars with approximately 30˚ of canal curvature were selected through geometric matching using micro-computed tomography. The samples were divided into three groups according to the number of up-and-down movements at the working length (1, 3, and 6 times; n = 24 each) and subdivided according to the instruments: JIZAI (#13/0.04 taper, #25/0.04 taper, and #35/0.04 taper) or TruNatomy (#17/0.02 taper, #26/0.04 taper, and #36/0.03 tape) (n = 12 each). The design, surface defects, phase transformation temperatures, nickel-titanium ratios, torque, force, shaping ability, and surface deformation were evaluated. Data were analyzed with the Kruskal-Wallis and Dunn's tests (α = 0.05).

RESULTS

The instruments had different designs and phase transformation temperatures. The 3 and 6 up-and-down movements resulted in a smaller upward force compared to 1 movement (p < 0.05). TruNatomy generated significantly less maximum torque, force, and surface wear than JIZAI (p < 0.05). However, TruNatomy exhibited a larger canal deviation (p < 0.05). No statistical differences in shaping ability were detected between different up-and-down movements.

CONCLUSIONS

Under laboratory conditions with JIZAI and TruNatomy, a single up-and-down movement at the working length increased the screw-in force of subsequent instruments in severely curved canals in the single-length instrumentation technique. A single up-and-down movement generated more surface defects on the file when using JIZAI. TruNatomy resulted in less stress generation during instrumentation, while JIZAI better maintained the curvature of root canals.

Evaluation of Cyclic Fatigue Resistance of Novel Replica-Like Instruments in Static Test Model

Introduction

The aim of our study is to comparatively analyze the canal cyclic fatigue resistance of widely used rotary file systems, including EndoArt Touch Gold (ETG), Perfect MTF Plus Gold (PPG), Fanta V-Taper Gold (FVG), and ProTaper Next (PTN).

Methods

Stainless steel canals with a 60° angle and a 3-mm curvature radius were specially prepared. The canals were shaped with each rotary file system and tested for resistance using a cyclic fatigue testing apparatus. The number of fracture cycles (NFC; K file tip separation) was measured. Data were analysed by one-way ANOVA and post hoc LSD tests.

Results

PTN and PPG rotary file systems exhibited the highest NFC. The NFC value for PTN was 589 ± 63, and for PPG, it was 507 ± 51.

Conclusion

The results of this study demonstrate that rotary file systems such as PTN and PPG exhibit higher cyclic fatigue resistance. ETG and FVG rotary file systems also possess generally acceptable cyclic fatigue resistance levels.

Phase Transformation and Mechanical Behaviour of Different Heat-Treated Nickel-Titanium Rotary Instruments

OBJECTIVES

This study evaluated the phase composition, phase transformation behaviour, and mechanical properties of five heat-treated NiTi instruments.

METHODS

ProTaper NEXT (M-wire, PTN), ProTaper Gold (Gold-wire, PTG), One Curve (C-wire, OC), EdgeTaper Platinum (Fire-wire, ETP), NeoNiTi (electrical discharge machining-wire, NNA), and ProTaper Universal (conventional wire, PTU, control) with #25-tip size were tested (n = 12/group) for cyclic fatigue resistance (number of cycles to failure; NCF) and torsional resistance (angle of rotation to fracture and maximum torque at fracture [ultimate torsional strength]). The geometry and fracture surfaces of the tested instruments were examined by scanning electron microscopy. The phase transformation temperature and phase composition of the instruments were evaluated using differential scanning calorimetry and X-ray diffraction. Data were statistically analysed using one-way ANOVA and Tukey's post hoc test, with the significance level set at 5%.

RESULTS

PTG showed the highest NCF (P < .05) at 37°C, while ETP exhibited the highest angle of rotation to fracture, ultimate torsional strength, and stiffness (P < .05). Scanning electron microscopy demonstrated typical clusters of fatigue striations and numerous cracks after cyclic fatigue fracture, whereas there was a concentric abrasion pattern with a dimple and microvoids at the centre after torsional fracture. In differential scanning calorimetry curves, austenite-finishing temperatures of heat-treated instruments were higher than 37°C, whereas that of PTU was lower than 37°C. PTU showed strong peaks of austenite at 25 and 37°C, whereas ETP showed a strong peak of R-phase at 25°C, but mostly austenite phase at 37°C in X-ray diffraction.

CONCLUSIONS

Geometry, alloy type, and phase transformation temperatures of NiTi instruments affected their mechanical behaviour.

CLINICAL RELEVANCE

PTG showed the highest NCF, suitable for markedly curved canals. ETP had the highest torsional resistance, appropriate for narrow and constricted canals.

Comparative Analysis of Surface Roughness and Plastic Deformation of Reciprocating Instruments after Clinical Use

This study assessed the surface topography and plastic deformation (PD) of new and used contemporary reciprocating instruments. Twenty-six WaveOne Gold (WOG) and EdgeOne Fire (EO) instruments were photographed under magnification. The instruments were randomly assigned to a control group of new instruments preserved for surface roughness analysis (n = 6 each), or to an experimental group to shape the root canal system of a single molar (n = 20 each), making a total of four groups (WOGnew, EOnew, WOGused, EOused). Used instruments were also photographed after instrumentation. The presence of fractures was registered. Preoperative and postoperative images were randomly ordered for evaluation. Two blinded calibrated examiners evaluated the presence of PD. Inter-observer agreement was calculated with the Kappa coefficient (K = 0.89). 3D profilometry was also used for the surface roughness analysis of six randomly selected instruments from the WOGused and EOused groups. Chi-square and two-way ANOVA tests were used to, respectively, compare PD and changes in surface roughness among the groups. No instruments fractured; however, a significantly greater percentage of EO instruments suffered plastic deformation than WOG instruments (p < 0.001), (OR = 11.09 (CI 95% 2.6-56.3)). The overall surface roughness was higher for most parameters in the EO instruments (p < 0.05). Single uses of EO instruments produced significantly higher chances of PD and increased surface roughness values compared to WOG.

Electrochemical Properties of Nickel-Titanium Rotary Endodontic Instruments

INTRODUCTION

Nickel-titanium rotary endodontic files have been commercially available for decades, but more recent innovations have introduced heat-treated and surface-treated files. This study investigated the corrosion properties of various nickel-titanium files in normal saline and sodium hypochlorite (NaOCl).

METHODS

Ten different file brands of size 40 with a 0.04 taper were subjected to electrochemical testing in 0.9% NaCl (saline) and 5.25% NaOCl at room temperature. The Open Circuit Potential (OCP) was observed for 1 hour followed by a cyclic polarization test from -300 to 700 mV and back to -300 mV (vs OCP). Nonparametric ANOVA and a pairwise comparison (P < .05) were used for statistical analysis of the OCP at 1 hour and the corrosion current (Icorr) obtained via the cyclic polarization test.

RESULTS

Significant differences (P < .05) were found between files with respect to OCP and Icorr in both solutions. Nine files exhibited significantly greater (P < .05) Icorrs in NaOCl than in saline. Conversely, pitting corrosion was observed in the saline solution but not NaOCl. Weak and/or moderate correlations existed between OCP and Icorr measures in the 2 solutions.

CONCLUSION

Significant differences in electrochemical properties were observed among the 10 brands of files. Overall, there was not a clear trend between conventional, heat-treated, or surface-treated files among OCP or Icorr in either solution.

Multimethod Analysis of a Novel Multi-coloured Heat-treated Nickel-Titanium Rotary System: Design, Metallurgy, Mechanical Properties, and Shaping Ability

INTRODUCTION

This study aimed to compare a new multicolored rotary system with four heat-treated rotary instruments using the multimethod approach.

METHODS

Three-hundred instruments of RCS Rainbow, Rotate, RaCe EVO, OneCurve, and ProTaper Ultimate systems were evaluated regarding their design (stereomicroscopy, scanning electron microscopy, and 3D surface scanning), metallurgy, and mechanical performance (cyclic fatigue, torsional resistance, bending and buckling resistance, and cutting ability). Unprepared surfaces after canal preparation of maxillary molars were evaluated using micro-computed tomography. Kruskal-Wallis and one-way analysis of variance post hoc Tukey tests were used for statistical comparisons (α = 5%).

RESULTS

Instruments exhibited variations in active blade length, number of spirals, and cross-sectional designs. RCS Rainbow showed specific phase transformation temperatures, highest bending (400.5gf) and buckling (286gf) resistance values, and lowest mean angle of rotation (529°) (P < .05). OneCurve exhibited superior cutting ability (8.4 mm) and longer time to fracture (112s). RaCe EVO displayed the lowest time to fracture (51s), maximum torque (1.2 N.cm), buckling (174gf), and bending resistance (261gf) values (P < .05). ProTaper Ultimate showed the highest torque (1.6 N.cm) and angle of rotation (611°) (P < .05), while its bending load (262gf) was comparable to RaCe EVO (P > .05). Rotate instrument showed intermediate values in the mechanical tests. No difference was observed regarding the unprepared canal surfaces (P > .05) CONCLUSIONS: RCS Rainbow demonstrates a trade-off between flexibility and other mechanical properties. Its dimensions exceeded those of other instruments, affording it higher torque resistance, yet concurrently reducing its flexibility, angle of rotation, and cutting ability. OneCurve stands out as a well-balanced choice by integrating geometric design and mechanical performance.

Cutting efficiency and corrosion resistance of heat-treated endodontic files after various disinfection protocols

The aim of this study is to evaluate the effect of various disinfection protocols on the cutting efficiency and chemical composition of ProTaper, Twisted File, Twisted File Adaptive, and Hedström files. Four experimental groups (n = 10) were presoaked in either enzymatic solution or 1% sodium hypochlorite for 30 min, followed by either 5 or 15 min of ultrasonic cleaning and then autoclaved. Resin-simulated canals with a single curvature of 38-40° were prepared by each instrument system. Cutting efficiency of each instrument was analyzed by subtracting the final weight from the initial weight of the resin blocks. Chemical compositions were studied by field emission scanning electron microscopy and X-ray energy-dispersive spectrometry. The cutting efficiency of Hedström, ProTaper, and Twisted File instruments decreased compared to their control groups (p < 0.05) whereas it did not change for Twisted File Adaptive. More corrosion was detected with longer ultrasonication time. No difference was observed regarding the pre-soaking media. Disinfection protocols exerted a significant overall effect on the performance of Hedström, ProTaper, and Twisted File instruments. Corrosion, microcracks, and crevices were evident on all tested instruments after disinfection protocols applied. All disinfection protocols, regardless of the pre-soaking media used or the ultrasonic cleaning time applied, have some effect on the cutting efficiency and the surface characteristics of the files.

Broken Instrument Removal Methods with a Minireview of the Literature

Instrument fracture in the root canal system is an unpleasant incident that may occur during root canal treatment. Comprehensive cleaning of the root canal system is often impossible in the presence of a broken instrument. Therefore, it is often imperative to remove the broken fragment from the root canal system. To date, various methods have been proposed for the removal of broken instruments from the root canal system. However, no consensus has been reached on a safe technique with a high success rate for broken instrument removal. This case series reports six cases of successful removal of broken instruments using different methods including the ultrasonic, tube-and-glue, tube-and-wire, tube-and-internal shaft, and the forceps techniques and also provides a brief review of the relevant literature.

The extended finite element method in endodontics: A scoping review and future directions for cyclic fatigue testing of nickel-titanium instruments

OBJECTIVES

The present study reviews the current literature regarding the utilization of the extended finite element method (XFEM) in clinical and experimental endodontic studies and the suitability of XFEM in the assessment of cyclic fatigue in rotary endodontic nickel-titanium (NiTi) instruments.

MATERIAL AND METHODS

An electronic literature search was conducted using the appropriate search terms, and the titles and abstracts were screened for relevance. The search yielded 13 hits after duplicates were removed, and four studies met the inclusion criteria for review.

RESULTS

No studies to date have utilized XFEM to study cyclic fatigue or crack propagation in rotary endodontic NiTi instruments. Challenges such as modelling material inputs and fatigue criteria could explain the lack of utilization of XFEM in the analysis of mechanical behavior in NiTi instruments.

CONCLUSIONS

The review showed that XFEM was seldom employed in endodontic literature. Recent work suggests potential promise in using XFEM for modelling NiTi structures.

Effect of Autoclave Sterilization on the Number of Uses and Resistance to Cyclic Fatigue of WaveOne Gold and Four Replica-Like Endodontic Instruments

This study aimed to evaluate the effect of autoclave sterilization on the integrity and instruments' fracture number after multiple uses and cyclic fatigue of the original WaveOne Gold (Dentsply Sirona Endodontics) compared to four replica-like instruments (TF4-Gold, Roll-Wave-Gold, W-File, and Micro-Gold). The instruments were analyzed by scanning electron microscope (SEM) before being used in root canal instrumentation (baseline). One hundred and fifty human molars, freshly extracted for orthodontic reasons or periodontal disease and with severe curvature (between 30° and 60°), were used. Fifty teeth were instrumented with 10 instruments from each group and were evaluated for integrity. After sterilization in an autoclave, the instruments were analyzed by SEM. This procedure was repeated twice more, totaling three rounds of instrumentation, sterilization, and SEM analysis. Ten unused instruments from each group were evaluated for resistance to cyclic fatigue in a static test using a motor and a device simulating a canal with a 60° curvature angle. The instruments were driven by the motor until separation, visually verified, and the time measured in seconds. Data were analyzed by Chi-square, one-way ANOVA, and Tukey analysis, considering a significance level of 5%. It was found that there was no statistically significant difference between the groups tested in the effect of sterilization on the number of uses. The SEM analysis showed distortions in the instruments after the 3rd use. There was a statistically significant difference in the cyclic fatigue test between the results of WaveOne Gold, TF4 Gold, and Roll Wave Gold compared to W File and Micro Gold (P  < 0.0001) and a statistically significant difference between the W File and Micro Gold groups (P  < 0.0001). In conclusion, this study affirmed that WaveOne Gold, TF4-Gold, and Roll-Wave-Gold instruments exhibit comparable cyclic fatigue resistance. Besides, all examined instruments can be reliably employed for up to two cases.

In vitro study of structural and chemical changes in two reciprocating files after multiple reuses and sterilisation

To use scanning electron microscopy and energy dispersive X-ray spectroscopy to evaluate the metallurgical-chemical changes of WaveOne Gold (WOG) and R-Motion (RM), after multiple uses. The instruments were divided into groups (n = 8): WOG and RM-control groups, new instruments; WOG1 and RM1; WOG2 and RM2; WOG3 and RM3 after instrumentation of 1, 2 or 3 molars, respectively. Burrs occurred mainly in the control group and after the first use. The RM files were found to have a higher nickel content, which increased during reuse, and a decrease in oxygen content with increasing reuse, in addition to calcium impregnation, which occurred in greater amounts in the corrosion areas in the WOG files. The presence of topographic and chemical changes was demonstrated, indicating that caution should be taken when reusing endodontic instruments to avoid fractures.

Comprehensive Assessment of Cyclic Fatigue Strength in Five Multiple-File Nickel-Titanium Endodontic Systems

The resistance of nickel-titanium endodontic instruments against cyclic fatigue failure remains a significant concern in clinical settings. This study aimed to assess the cyclic fatigue strength of five nickel-titanium rotary systems, while correlating the results with the instruments' geometric and metallurgical characteristics. A total of 250 new instruments (sizes S1/A1, S2/A2, F1/B1, F2/B2, F3/B3) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-Files systems underwent mechanical testing. Prior to experimental procedures, all instruments were meticulously inspected to identify irregularities that could affect the investigation. Using a stereomicroscope, design characteristics such as the number of spirals, length, spirals per millimeter, and average helical angle of the active blade were determined. The surface finishing characteristics of the instruments were examined using a scanning electron microscope. Differential scanning calorimetry was employed to establish the instruments' phase transformation temperatures, while energy-dispersive X-ray spectroscopy was utilized to analyze the elemental composition of the alloy. The instruments were subjected to cyclic fatigue testing within a stainless steel non-tapered artificial canal featuring a 6 mm radius and 86 degrees of curvature. Appropriate statistical tests were applied to compare groups, considering a significance level of 0.05. The assessed design characteristics varied depending on the instrument type. The least irregular surface finishing was observed in U-Files and Premium Taper Gold files, while the most irregular surface was noted in Go-Taper Flex. All instruments exhibited near-equiatomic proportions of nickel and titanium elements, whereas ProTaper Universal and U-Files instruments demonstrated lower phase transformation temperatures compared to their counterparts. Larger-sized instruments, as well as ProTaper Universal and U-Files, tended to display lower cyclic fatigue strength results. Overall, the design, metallurgical, and cyclic fatigue outcomes varied among instruments and systems. Understanding these outcomes may assist clinicians in making more informed decisions regarding instrument selection.

Surface roughness and cyclic fatigue resistance of a novel shaping system: An in-vitro study

Recently developed Nickel-Titanium (NiTi) instruments with practical changes have resulted in safer instrumentation. In addition, topographical features on the file surface are a contributing factor to clinical durability. Therefore, this study aimed to investigate both the cyclic fatigue resistance and the roughness change of MTwo and Rotate instruments (VDW, Munich, Germany). Each instrument (n = 6/each group) was scanned with an atomic force microscopy prior to and after instrumentation. In addition, cyclic fatigue testing was conducted for each instrument (n = 11/each group) with stainless-steel blocks, including 45°-60°-90° degrees of curvature milled to the instruments' size. The roughness parameters increased for both systems after instrumentation (p<0.05). Both systems presented an increased roughness following instrumentation (p<0.05). The cyclic fatigue resistance was lowest at 90° for both systems (p<0.05), whereas the Rotate files presented a higher resistance than that of the Mtwo files (p<0.05). Compared to the Mtwo files, Rotate files presented better resistance, while the resistance decreased as the curvature increased.

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.

Substance P/calcitonin gene-related peptide and their receptors expression in human periodontal ligament after root canal preparation with five different systems

AIM

The purpose of this study was to quantify the effect of five different root canal preparation instruments on Substance P (SP), Calcitonin gene-related peptide (CGRP) and their receptors expression in healthy human periodontal ligament.

METHODOLOGY

STROBE guidelines were used to design a study using 60 periodontal ligament samples obtained from healthy lower premolars where extraction was indicated for orthodontic reasons. Prior to extraction 40 of these premolars were equally divided into four groups and root canals were prepared using different systems: Mtwo, Reciproc Blue, HyFlex EDM and Plex-V. Ten premolars were prepared with hand files and served as a positive control group. The remaining 10 premolars where extracted without treatment and served as a negative control group. All periodontal ligament samples were processed to measure the expression of SP, CGRP and their receptors by radioimmunoassay. Kruskal-Wallis and Duncan tests were performed to determine statistically significant differences between the groups for each variable.

RESULTS

Greater expression of all the peptides measured were found in the hand-file preparation group, followed by the Reciproc Blue, Mtwo, HyFlex EDM and Plex-V groups. The lower SP, CGRP and their receptors values were for the intact teeth control group. Kruskal-Wallis test showed statistically significant differences amongst groups (p < .001). Dunn post-hoc tests showed statistically significant differences in SP, CGRP and their receptors expression between the intact teeth and the hand-file and Reciproc Blue groups. Hand-file group showed significant differences with the other groups, except with Reciproc Blue, where no differences were observed in any of the peptides measured. Finally, no differences were observed between Plex-V and HyFlex in any of the peptides measured.

CONCLUSIONS

Root canal preparation with hand files and Reciproc Blue generates the highest expression of SP, CGRP, NK1 and CGRP1R in human periodontal ligament, whilst Plex-V and HyFlex maintain the basal expression of neuropeptides and their receptors. Mtwo showed intermediate results between Reciproc Blue and HyFlex.

Microcomputed tomography analysis of curved root canal preparation when coronal flaring and glide path files used with heat-treated nickel titanium rotary files

The objective was to evaluate the effect of glide path and coronal flaring on the dentin volume removal and percentage of touched walls in curved canals using two heat-treated rotary files. The mesiobuccal canal of forty-eight, randomly selected, extracted mandibular molars was divided into two groups of 24 each, according to the type of instrument used (RACE EVO and EdgeSequel rotary files). Each group was further divided into three subgroups; Group (A): Control using one file shaped to 04/30, Group (B) with a glide path (EdgeGlidePath (EGP)), and Group (C): with a glide path and coronal flaring (EGP and EdgeTaper Platinum (ETP) SX file respectively). The root canals were then instrumented using the assigned instruments. The assessment was carried out using micro-CT. The comparison of the mean values of the tested groups about dentin volume removal and percentage of untouched walls did not reach statistical significance (p<0.05). Glide path and coronal flaring had an insignificant effect on the dentin volume removal and percentage of untouched walls in curved canals.

Phase transformation behavior and mechanical properties of HyFlex EDM nickel-titanium endodontic rotary instrument: Evaluation at body temperature

Background/purpose

Temperature-dependent phase compositional changes influence the mechanical properties of heat-treated nickel-titanium (NiTi) rotary instruments. This study evaluated the phase composition, bending properties, and cyclic fatigue resistance of HyFlex EDM NiTi rotary instruments against differently heat-treated and non-heat-treated NiTi instruments at body temperature (BT).

Materials and methods

HyFlex EDM OneFile (EDM) instruments, heat-treated HyFlex CM (CM) and Twisted File (TF) instruments, and non-heat-treated K3 instruments (size #25/.08) were subjected to differential scanning calorimetry, and the martensitic, R-phase, and reverse transformation starting and finishing temperatures were determined. A cantilever bending test and a cyclic fatigue test were conducted at BT (37 °C ± 1.0 °C), and the bending load and number of cycles to failure (NCF) were recorded. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney U tests (α = 0.05).

Results

TF and K3 had reverse transformation finishing temperatures lower than BT, while those for EDM and CM were higher than BT. The bending loads at a 0.5 mm deflection were in the order of EDM < TF < CM < K3 (P < 0.05), and those at a 2.0 mm deflection were EDM < CM and TF < K3 (P < 0.05). EDM had the highest NCF among the four instruments (P < 0.05).

Conclusion

The EDM instrument had a reverse transformation finishing temperature higher than BT indicating its martensite/R-phase composition at BT. The EDM instrument had superior flexibility and greater resistance to cyclic fatigue than the CM, TF, and K3 instruments at BT.

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

INTRODUCTION

This 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.

METHODS

Reciproc 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%.

RESULTS

RMT 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.

CONCLUSIONS

Under 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.

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.

Comparative evaluation of cyclic fatigue resistance of thermomechanically treated NiTi rotary instruments in simulated curved canals with two different radii of curvature: An in vitro Study

Background

This study aimed to compare the effect of heat treatment on the cyclic fatigue resistance of three different nickel-titanium rotary file systems: TruNatomy, HyFlex CM, and NeoEndo flex in simulated curved canals at two different radii of curvatures.

Materials and Methods

A total of 60 NiTi rotary files of three types were used, and the samples were divided into three groups TruNatomy, HyFlex CM, and NeoEndo flex. All the instruments were subjected to cyclic fatigue testing using a stainless steel custom-made canal model with a 60° angle of curvature and two radii of curvature 5 mm and 3 mm; the number of cycles to fracture and length of the fractured segment was measured. The separated instruments were subjected to fractographic analysis under scanning electron microscope.

Results

The number of cycles to failure to fracture a file at a 3 mm radius of curvature is significantly less as compared to a 5 mm radius of curvature (HCM > TRN > NE).

Conclusion

Within the limitation of the present study, there was a positive correlation between the radius of curvature and fatigue life of NiTi files.

Evaluation of the Ability of 3 Reciprocating Instruments to Remove Obturation Material: A Micro-Computed Tomography Study

INTRODUCTION

The purpose of this study was to evaluate the ability of the Reciproc, Reciproc Blue, and WaveOne Gold systems to remove filling material during endodontic retreatment of extracted human mandibular premolars.

METHODS

Thirty-nine teeth were instrumented with the Protaper Universal System to the F3 file and filled with the Tagger hybrid technique using an F3 gutta-percha cone and AH Plus cement. At the end of this period, the teeth were scanned with micro-computed tomography before and after removal of the filling material from the root canals. The teeth were divided into 3 groups (n = 13) based on the apical volume, depending on the systems used to remove the filling material. Group GR: Reciproc 40/.06; Group GRB: Reciproc Blue 40/.06; and Group GWG: WaveOne Gold 35/.06. The results were statistically analyzed using the tests of Kruskal-Wallis, Duncan, and analysis of variance at a significance level of 5%.

RESULTS

The results showed that there were no significant differences between the amounts of filling material removed, either for the apical and middle regions alone or in the overall evaluation for the 3 groups (P = .97). The time evaluation statistically showed that the GR and GWG groups required less time to clean the root canals than the GRB group.

CONCLUSIONS

Reciproc R40 files and WaveOne Gold Medium files required less time for endodontic treatment than Reciproc Blue R40 files. There was no difference in the ability to remove obturation material between the 3 instruments. No instrument was able to completely remove the filling material from the root canals.

Microcomputed tomographic evaluation of 6 NiTi files on the pericervical dentin and the smallest dentin thickness zones in mesial root canals of mandibular molars: an in vitro study

OBJECTIVE

The aim of this study was to evaluate six files on the pericervical dentin (PCD) and the smallest dentin thickness zones (SDTZ) in mesial root canals of mandibular molars.

MATERIALS AND METHODS

Sixty mandibular molars with two mesial canals and Vertucci configuration were aleatory allocated in 6 experimental groups of 10 molars and 20 root canals. Specimens were scanned before instrumentation using the SkyScan 1275 (Bruker microCT, Kontich, Belgium). Group 1 was treated with WaveOne Gold (WG), group 2 with Reciproc Blue (RB), group 3 with TRUShape (TS), group 4 with XP-endo Shaper (XP), group 5 with iRace (IR), and group 6 with TruNatomy (TN). After instrumentation, the molars were scanned again and the images recorded were reconstructed with the NRecon v.1.7 (Bruker micro-CT) and analyzed with CTAn v.1.20.8 software (Bruker micro-CT) quantifying the changes produced in the surface, volume, structure thickness, SMI, and centroids at the Pericervical Dentin area of the root canals (PCD) located from the root canal orifices at the floor of the pulp chamber to 4 mm in the apical direction, and the changes in the Smallest Dentin Thickness Zones (SDTZ) located (from the furcation to 4 mm and 7 mm in the apical direction. The data obtained were compared using Wilcoxon and ANOVA with a 5% significance level.

RESULTS

XP and TN were similar in all the parameters (P >.05) at the PCD, but TN showed significant differences from WG, RB, TS, and IR (P <.05), while XP showed significant differences from WG (P <.05) in volume, surface, and structure thickness. Regarding the changes in the SDTZ, the amount of dentin removed was similar between the groups in both canals at the middle 1/3, at the cervical 1/3 for MB canals, and in ML canals for RB, TS, XP, IR, and TN (P>.05). The action of WG was significantly different from that of XP and TN in the cervical 1/3 of the ML canal (P <.05).

CONCLUSIONS

XP and TN rotatory files with small taper and volume maintained better with minor changes at the PCD and SDTZ, while WG reciprocation file produced the largest change. All the files were maintained centered at the PCD, and their performances were safe with a minimal thickness higher 0.5 mm at the SDTZ, and without risk of perforation.

TRIAL REGISTRATION

No clinical trials were indicated in this study.

CLINICAL RELEVANCE

The choice of endodontic files is a relevant factor in the conservative performance of root canal treatments.

Effect of Heat Treatment on Mechanical Properties of Nickel-Titanium Instruments

INTRODUCTION

The aim of this study was to evaluate the torsional resistance, cyclic fatigue resistance, and bending stiffness of nickel-titanium (NiTi) file systems with different heat treatments and cross-sectional designs.

METHODS

WaveOne Primary treated with memory-triple (MT) heat treatment (WOMT) was compared with WaveOne Primary (WO) and WaveOne Gold Primary (WOG). Torsional resistance test was performed using a customized device, and the distortion angle, ultimate strength, and toughness were evaluated. For cyclic fatigue resistance test, the instruments were reciprocated with continuous 4 mm up-and-down movement until fracture in a customized device, and the time to fracture was compared. Fracture surfaces of each group were examined under the scanning electron microscope. Bending stiffness was measured using a custom-made device. The results were analyzed using one-way analysis of variance and the Tukey's post hoc comparison at a significance level of 95%.

RESULTS

WOMT showed higher ultimate strength and toughness than the other systems (P < .05). WOMT also showed highest cyclic fatigue resistance among the tested groups (P < .05). WO had the highest bending stiffness than others, whereas WOMT had a larger residual angle than others (P < .05).

CONCLUSIONS

This new MT heat treatment technique makes NiTi file more flexible and improves its mechanical properties. In addition, the effect of heat treatment on flexibility was found to be more significant than that of the cross-sectional area.

Using manual versus mechanized glide path instruments and ProTaper Gold versus ProTaper Next systems in curved canals: micro-CT study

The aim of this study was to evaluate the root canal shaping effect of ProTaper Gold (PTG) versus ProTaper Next (PTN) instrumentation systems, and of a manual #15 K-type file (K15) versus the ProGlider (PG) mechanized instrument for glide path creation, in severely curved mesial canals. Twenty-four mandibular molars with two separate mesial canals were anatomically matched using computed tomographic scanning, and then divided into two groups (n=12) according to the glide path instrument used, either K15 or PG. In all teeth, the PTG system was used to prepare the mesiobuccal canal, and the PTN, the mesiolingual canal. The teeth were scanned by computed microtomography, before and after root canal preparation, and the values of the initial volume, final volume, volumetric variation, untouched walls, and canal transportation variables were determined. The data were analyzed using the two-way ANOVA test, and the Tukey test for multiple comparisons. There was no significant difference among the study groups regarding volumetric variation or root canal transportation, either in the cervical, middle or apical thirds, or in the entire root canal (p>0.05). In the apical third, the percentage of untouched walls was significantly higher in groups using K15 than in those using PG (p<0.05), namely 33.144% and 23.285%, respectively, irrespective of the instrumentation system. In the other regions, there was no difference between K15 and PG regarding this variable. It was concluded that PG was associated with a lower rate of untouched walls in the apical region than K15.

The efficacy of various irrigation techniques on the removal of double antibiotic paste from simulated immature roots and the amount of apically extruded debris

OBJECTIVE

This study evaluated the effect of the XP-Endo Finisher (XPF), passive ultrasonic irrigation (PUI) and conventional irrigation using side-vented needle (SVN) on the amount of apically extruded debris and canal cleanliness following the removal of double antibiotic paste (DAP) from immature root canal models.

MATERIAL AND METHODS

Forty-eight extracted mandibular premolars were drilled using peeso drills to simulate immature apices. The canals were filled with DAP and were randomly assigned into 3 groups according to the DAP removal method: XPF, PUI, and SVN (n = 16). The amount of extruded debris was assessed with an analytical balance then roots were split longitudinally and imaged using stereomicroscope to evaluate the residual medicament. Data were statistically analyzed using Kruskal-Wallis and Dunn's test. Spearman's correlation coefficient was used to determine significant correlation between extruded debris and the residual DAP scores.

RESULTS

There was no significant difference between debris extrusion values for all groups (P value 0.237). For canal cleanliness, the amount of remaining DAP was significantly lower in the XPF and PUI compared to SVN (P value < 0.001). A non-significant positive (direct) correlation was found between the amounts of apically extruded debris and residual DAP scores (P value 0.087).

CONCLUSION

XPF and PUI were associated with better canal cleanliness during removal of DAP, no difference could be found between the three irrigation techniques regarding the debris extrusion.

Evaluation of cyclic and torsional fatigue resistance of several heat-treated reciprocating nickel-titanium instruments

This study investigated the cyclic fatigue and torsional resistance of Unicone Plus (UCP 25.06), Unicone (UC 25.06), Reciproc Blue (RB 25.08) and Wave One Gold (WOG 25.07) performed at body temperature (35° ± 1°C). Time and number of cycles to fracture (NCF), as well as torque and angular deflection were recorded. Fractured surfaces were evaluated by scanning electron microscopy (SEM). Data were analysed using one-way ANOVA and Holm-Sidak's tests for multiple comparison. The RB had a significantly higher time to fracture, followed by the WOG and UCP (p < 0.05). Regarding the NCF, there was no significantly difference between RB and WOG (p > 0.05). UC presented highest torque values and the lowest angular deflection (p < 0.05). SEM analysis demonstrated typical failures features in both cyclic and torsional fatigue tests. Overall, UC had the lowest time, NCF and angular deflection at fracture. RB presented the highest time to fracture and angular deflection values.

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.

Influence of endodontic motors on the behaviour of root canal shaping instruments: an in vitro comparative study

AIMS

The endodontic literature reports a lot of comparative study on endodontic instruments, concerning as well their geometry, instrumental dynamics, material, mechanical behavior or heat treatment. However, to our knowledge, no study has focused on the influence of endodontic motors on the shaping abilities of endodontic instruments. Thus, the aim of this study was to analyze the influence of the endodontic motors on root canal shaping instruments.

METHOD

Dual Move (MICRO-MEGA, Besançon, France), Canal Pro CL2i (COLTENE, Alstätten, Suisse), Canal Pro Jeni Motor (COLTENE, Alstätten, Suisse), Ai Motor (WOODPECKER, Guilin, China), Wave One motor (VDW, Postfach, Munich) and Smart A (WOODPECKER, Guilin, China) were pre-clinically compared in continuous rotation and reciprocating motion on a traction/compression bench using resin blocks. Canal shaping in continuous rotation and reciprocating motion were performed with One Curve and One RECI instruments (MICRO-MEGA, Besançon, France), respectively. The penetration/removal forces, making it possible to objectify the cutting effect and screwing effect of the instruments during root canal shaping, were analyzed.

RESULTS

The results showed (i) that endodontic motors influence the mechanical behavior of endodontic instruments, (ii) that the influence of the motors is essentially felt during reciprocating motion and (iii) that the reciprocating angles influence the mechanical behavior of endodontic instruments.

CONCLUSION

Only endodontic instruments are widely studied in literature while endodontic motors have a direct influence on root canal treatment. This study analyzes the influence of the endodontic motors on root canal shaping instruments. This study tends to demonstrate that Jeni Motor could optimize the mechanical behavior of endodontic instruments.

In vitro evaluation of filling material removal and apical debris extrusion after retreatment using Reciproc blue, Hyflex EDM and ProTaper retreatment files

OBJECTIVES

To evaluate the amount of remaining filing material and apical debris extrusion after retreatment using Reciproc Blue, Hyflex EDM and ProTaper Retreatment Files.

MATERIALS AND METHODS

Thirty-six extracted permanent mandibular first molars with moderately curved mesial roots were selected. Mesiobuccal canals were prepared using the ProTaper Next system up to size X2 and filled using gutta-percha and Adseal sealer via cold lateral compaction. Teeth were randomly divided into three equal groups (n = 12): Group 1: Reciproc Blue (RB)(VDW, Germany), Group 2: Hyflex EDM (HEDM)(Coltene/Whaledent, Switzerland), Group 3: ProTaper Universal Retreatment file system + ProTaper Next file system (PTUR + PTN)( Dentsply Maillefer, Switzerland). Eppendorf tubes were used to collect the apically extruded debris. Cone-beam computed tomographic scans were taken prior to and after retreatment and the volume of remaining filling material was assessed at the coronal, middle and apical levels. Statistical analysis was performed using the Kruskal-Wallis test, Friedman's test and Wilcoxon Sign Rank test. Significance level was set at p value 0.05.

RESULTS

There were no statistically significant differences among the three groups in the reduction of the volume of the filling material or in the amount of apically extruded debris.

CONCLUSION

All the tested filing systems showed similar efficacy in removing the filling material, however, none of them could achieve its complete removal. Apical extrusion of debris occurred with all the systems used with no significant difference between the three groups.

Phase transformation and mechanical properties of heat-treated nickel-titanium rotary endodontic instruments at room and body temperatures

BACKGROUND

The aim of this study was to evaluate the phase composition, phase transformation temperatures, bending property, and cyclic fatigue resistance of different heat-treated nickel-titanium (NiTi) rotary instruments with the same tip diameter and taper at room (RT; 25 ± 1 °C) and body (BT; 37 ± 1 °C) temperatures.

METHODS

Five heat-treated NiTi rotary instruments, HyFlex EDM (EDM), HyFlex CM (CM), Vortex Blue (VB), RE file CT (RE) and JIZAI, and a non-heat-treated NiTi rotary instrument (Mtwo) with a size 40, 0.04 taper were investigated. Temperature-dependent phase transformation was examined with differential scanning calorimetry (DSC). The bending loads of the instruments at RT and BT were evaluated using a cantilever-bending test. Cyclic fatigue resistance at RT and BT was measured using a dynamic test, during which the instruments were rotated in combination with a 2-mm back-and-forth motion in an artificial curved canal, and the number of cycles to failure (NCF) was determined. The results were analyzed using two-way repeated measures analysis of variance, a simple main effect test, and the Bonferroni test (α = 0.05).

RESULTS

DSC results indicated that EDM and Mtwo were primarily composed of martensite/R-phase and austenite, respectively, while the other heat-treated instruments were composed of a mix of martensite/R-phase and austenite at the tested temperatures. Regardless of the temperature setting, the bending loads of heat-treated instruments were significantly lower than those of Mtwo (p < 0.05). EDM showed the lowest bending loads and highest NCF at both temperatures (p < 0.05). CM, VB, and JIZAI showed significantly higher bending loads at BT than at RT (p < 0.05). The NCF of all the heat-treated instruments, except VB, was lower at BT than at RT (p < 0.05). At BT, the NCF of CM, VB, RE, and JIZAI were not significantly higher than that of Mtwo (p > 0.05).

CONCLUSIONS

Heat-treated NiTi instruments exhibited lower bending loads and higher NCF values than Mtwo. However, this tendency was less pronounced at BT than at RT, especially in the NCF values of instruments with a mixture of martensite/R-phase and austenite phases at the tested temperatures.

Effect of Proximal Caries-driven Access on the Biomechanical Behavior of Endodontically Treated Maxillary Premolars

INTRODUCTION

This study investigated the effects from the carious cavity and access from it on the fracture resistance of endodontically treated maxillary premolars using finite element analysis (FEA).

METHODS

A maxillary premolar was used to compare 3 types of access cavity related to having a proximal carious defect: caries-driven access (CDA), conservative access that has a mesial component (MCA), as well as traditional access with the same mesial component (MTA). Cyclic loading was simulated on the occlusal surface, and number of cycles until failure (NCF) was compared with the intact tooth model (IT). Mathematical analysis was done to evaluate the stress distribution patterns and calculated maximum von Mises (vM) and maximum principal stresses (MPS), with emphasis on pericervical region as a specific area of interest.

RESULTS

Maximum vM registered on the IT was 6.14 MPa. CDA provided the highest NCF with 92.28% of the IT, followed by MCA (84.90%) and MTA (83.79%). The vM and MPS analysis showed that the stress values and patterns are affected more by the proximity of the occlusal load to the tooth/restoration interface. Concerning the pericervical region, maximum vM was registered for IT (4.11 MPa), followed by CDA (4.85 MPa) and then MCA (8.13 MPa) and MTA (8.61 MPa), whereas the MPS analysis revealed that CDA showed the highest magnitude of tensile stresses.

CONCLUSIONS

A proximal CDA benefits the mechanical properties of maxillary premolars; however, its impact on the biological aspect should be assessed to provide a ruling for/against it.

Nickel ion release and surface analyses on instrument fragments fractured beyond the apex: a laboratory investigation

BACKGROUND

To analyse the changes in surface and nickel ion release characteristics of fractured root canal shaping instruments in a simulated body fluid environment.

METHODS

A total of 54 new instruments were studied. The instrument groups consisted of five different NiTi alloys and a stainless-steel alloy. To standardize instrument fracture, a torsional type of failure was created on each instrument. The fractured specimens of each instrument group were randomly divided into three static immersion subgroups of 1 h, 7-day, and 30-day (n = 3). Simulated body fluid (SBF) was prepared to mimic human blood plasma by Kokubo&Takadama protocol for ex situ static immersions at 37ºC. The surfaces were examined via scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. To determine the quantitative ion release, the retrieved SBFs were analyzed using inductively coupled plasma mass spectrometry. Two-way ANOVA and Tukey post hoc tests sought the statistical significance of the nickel ion values(p < 0.05).

RESULTS

In 1 h of immersion, the newly formed structures, exhibiting mostly oxygen signals, were widespread and evident on NiTi surfaces. In contrast, fewer structures were detected on the SS surface in that subgroup. In 7 days of immersion, a tendency for a decrease in the density of the new structures was revealed in NiTi groups. The oxygen signals on NiTi group surfaces significantly increased, contrary to their decrease in SS. Signals of sodium, chlorine, and calcium were detected, indicating salt precipitates in groups. In 30 days of immersion, salt precipitates continued to form. The Ni-ion release values in all instrument groups presented significant differences in comparison to the SBF control in all immersion periods(p < 0.001). No significant differences were observed in immersion time periods or instrument groups(p > 0.05).

CONCLUSIONS

Within the limitations of the presented study, it was concluded that the fractured SS and NiTi root canal instruments release Ni ions in contact with body fluid. However, the Ni ion release values determined during the observation periods are lower than the critical toxic or allergic thresholds defined for the human body. This was due to the ionic dissolution cycle reaching a stable state from 1-hour to 30-day exposure to the body fluid of fractured instruments.

Mechanical properties evaluation of metacarpophalangeal joint prosthesis with new titanium-nickel memory alloy: a cadaver study

OBJECTIVE

Ni-Ti memory alloys are unusual materials for hard-tissue replacement because of their unique superelasticity, good biocompatibility, high strength, low specific gravity, low magnetism, wear resistance, corrosion resistance and fatigue resistance. The current study aims to evaluate its mechanical properties and provide biomechanical basis for the clinical application of the prosthesis.

METHODS

Ten adult metacarpophalangeal joint specimens were randomly divided into a prosthesis group (n = 5, underwent metacarpophalangeal joint prosthesis) and a control group (n = 5, underwent sham operation). Firstly, the axial compression strength was tested with BOSE material testing machine to evaluate its biomechanical strength. Secondly, these specimens were tested for strain changes using BOSE material testing machine and GOM non-contact optical strain measurement system to evaluate the stress changes. Thirdly, fatigue test was performed between groups. Lastly, the mechanical wear of the metacarpophalangeal joint prosthesis was tested with ETK5510 material testing machine to study its mechanical properties.

RESULTS

Axial compression stiffness in the prosthesis group was greater than that in the control group in terms of 30 ° and 60 ° flexion positions (P < 0.05). There was no statistically significant difference between two groups with regards to axial compression stiffness and stress change test (P > 0.05). In the fatigue wear test, the mean mass loss in the prosthesis group's prosthesis was 17.2 mg and 17.619 mm3, respectively. The mean volume wear rate was 0.12%. There was no statistically significant difference in the maximum pull-out force of the metacarpal, phalangeal, and polymer polyethylene pads between the prosthesis group and the control group specimens.

CONCLUSIONS

Ni-Ti memory alloy metacarpophalangeal joint prosthesis conforms to the biomechanical characteristics of metacarpophalangeal joints without implants, and the fatigue strength can fully meet the needs of metacarpophalangeal joint activities after joint replacement.

Centric versus eccentric engine-driven endodontic instrument design for microbial load reduction-A systematic review and meta-analysis of randomised clinical trials

This systematic review assessed the clinical influence of centric and eccentric engine-driven instrument design for reduction in microbial load in infected root canal system. The literature search was conducted in electronic databases (PubMed, Cochrane Library, Scopus, Lilacs and Google Scholar) and grey literature till June 2022. The search strategy followed the PRISMA 2020 guidelines. Qualitative and quantitative synthesis was conducted based on the guidelines of the Cochrane Handbook. The risk of bias was assessed using the revised Cochrane criteria and quality of evidence was conducted using the Grading of Recommendation Assessment, Development and Evaluation tool. Out of 28 papers, only five papers met the inclusion criteria of this review. Studies showed reduction in microbial load after instrumentation using centric or eccentric instruments with no statistically significant difference in the meta-analysis. In conclusion, there is low-grade evidence suggesting that microbial reduction is similar using centric and eccentric instruments.

The efficacy of three passive ultrasonic irrigation systems on intracanal medicament removal in a novel standardised three-dimensionally printed model

This study compared the efficacy of several passive ultrasonic irrigation (PUI) systems in removing intracanal medicament using 3-dimensionally printed root canal model assembled with dentin specimen. After the placement of the model in the agar container (37°C), the intracanal medicament was removed using three different PUI instruments including CK file, Irrisafe and Endosonic Blue. Then, the area coated by the medicament and the volumetric percentage of the remaining medicament was measured. Irrisafe and Endosonic Blue showed higher removal efficacy than CK and the control regarding both the coated area and remaining volume (p < 0.05). CK showed the lowest efficacy among the tested PUI systems (p > 0.05). Notably, Endosonic Blue group showed the smallest coated area among the tested groups (p < 0.05). Conclusively, PUI systems made of nickel-titanium alloy with small dimensions, such as Endosonic Blue, have advantages for the removal of intracanal medicaments from curved root canals.

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.

A review of the latest developments in rotary NiTi technology and root canal preparation

The introduction of nickel-titanium (NiTi) mechanical instruments dramatically changed clinical endodontics over the last few decades. Before NiTi, it was necessary to use more instruments to create an ideal root canal shape, and many approaches, sequences and techniques were developed over the years. Recently, NiTi endodontic instruments have undergone a series of changes brought about by modifications in design, surface treatments, and thermal treatments to improve their root canal preparation outcomes and reduce associated canal preparation risks during root canal treatment. Heat treatment is one of the most fundamental approaches to improving the fatigue resistance and flexibility of NiTi endodontic instruments. In addition, new kinematics have been developed to offer greater safety and efficiency. This narrative review describes the general properties and manufacturing of NiTi instruments, and the mechanical system evolution of NiTi instruments.

Comparative Evaluation of Extrusion of Apical Debris in Primary Maxillary Anterior Teeth Using Two Different Rotary Systems and Hand Files: An In Vitro Study

Successful outcome of pulp therapy depends on good chemomechanical preparation of the canals. This is completed with the help of various upcoming rotary and hand files. However, during this preparation, there might be an apical extrusion of the debris which may result in postoperative complications. The aim of this study was to evaluate and compare the number of debris apically extruded during canal preparation using two different pediatric rotary file systems and conventional hand file systems in primary teeth. 60 primary maxillary central incisors that were extracted due to trauma or untreated dental caries with no signs of resorption were taken. Canal preparation was executed using three different file systems: Group A: Group A hand K file system, Group B Kedo S Plus, Group C Kedo SG Blue. For each of these files using the Myers and Montgomery model, the pre- and post-weight of the eppendorf tube was assessed to quantify the number of apical debris. The maximum extrusion of apical debris was noticed with the Hand K-file system. The least debris was noticed in the Kedo S Plus file system. Statistical analysis revealed that there were highly significant differences in apical extrusion and debris when comparing hand files and rotary files and also between the two rotary files used. Apical debris collection is an unavoidable outcome of canal instrumentation. Among the file systems compared, rotary files had lesser extrusion when compared to hand files. Among the rotary files, Kedo S plus showed normal extrusion compared to SG Blue.

Thermal Behavior Changes of As-Received and Retrieved Bio-Active® (BA) and TriTanium® (TR) Multiforce Nickel-Titanium Orthodontic Archwires

Multiforce nickel-titanium (NiTi) orthodontic archwires release progressively increasing forces in a front-to-back direction along their length. The properties of NiTi orthodontic archwires depend on the correlation and characteristics of their microstructural phases (austenite, martensite and the intermediate R-phase). From a clinical and manufacturing point of view, the determination of the austenite finish (Af) temperature is of the greatest importance, as in the austenitic phase, the alloy is most stable and exhibits the final workable form. The main purpose of using multiforce orthodontic archwires is to decrease the intensity of the applied forces to the teeth with a small root surface area, such as the lower central incisors, and also provide forces high enough to move the molars. With the optimally dosed forces of multiforce orthodontic archwires in the frontal, premolar and molar segments, the feeling of pain can be reduced. This will contribute to the greater cooperation of the patient, which is of utmost importance to achieve optimal results. The aim of this research was to determine the Af temperature at each segment of as-received and retrieved Bio-Active^® and TriTanium^® archwires with dimensions of 0.016 × 0.022 inches, investigated by the differential scanning calorimetry (DSC) method. A classical Kruskal-Wallis one-way ANOVA test and multi-variance comparison based on the ANOVA test statistic using the Bonferroni corrected Mann-Whitney test for multiple comparisons were used. The incisor, premolar and molar segments have different Af temperatures, and they decrease from the anterior to posterior so that the posterior segment has the lowest Af. Bio-Active^® and TriTanium^® with dimensions of 0.016 × 0.022 inches can be used as first leveling archwires by additional cooling and are not recommended for use on patients with mouth breathing.

An in vitro comparison of alterations in surface topographies of three different rotary files after root canal preparation with different irrigating solutions: Atomic force microscopic study

Objectives

The objective of the study was to evaluate and compare the surface topographies of WaveOne Gold (WOG), FlexiCON X1, and EdgeOne Fire (EOF) reciprocating files before and after root canal instrumentation using different irrigating solutions.

Materials and Methods

Forty-eight extracted mandibular molars were selected and randomly assigned into three groups (n = 16) based on the file system used and each group was divided into two subgroups based on the irrigants used during root canal treatment. (Group-1: WOG; Group-2: FlexiCON X1; Group-3: EOF; Subgroup-A: 3% sodium hypochlorite [NaOCl] +17% ethylenediaminetetraacetic acid [EDTA]; Subgroup-B: Citra wash as irrigating solutions). The surface topography of the files was analyzed using atomic force microscope before and after instrumentation. Average roughness and root mean square roughness were calculated. Independent and paired t-tests and one-way analysis of variance with Tukey's post hoc were used for statistical analysis.

Results

Atomic force microscopy results showed an increase in surface roughness after instrumentation, EOF showing the highest roughness. Citra wash showed more roughness compared to NaOCl and EDTA together. However, the surface roughness between the experimental groups WOG and EOF are statistically insignificant and this insignificance was also seen among subgroups (P>0.05).

Conclusion

Instrumentation with various irrigating solutions affected the surface topography of EOF, WOG, and FlexiCON X1 reciprocating files.

Characterization of the file-specific heat-treated ProTaper Ultimate rotary system

AIM

To compare design, metallurgy and mechanical performance of the ProTaper (PT) Ultimate system with instruments of similar dimensions from the ProGlider, PT Gold and PT Universal systems.

METHODOLOGY

New PT Ultimate instruments (n = 248) were compared with instruments of similar dimensions from ProGlider (n = 31), PT Gold (n = 155) and PT Universal (n = 155) systems regarding their number of spirals, helical angle, blade symmetry, tip geometry, surface finishing, nickel/titanium ratio, phase transformation temperatures and mechanical performance. One-way anova and nonparametric Mood's median tests were used for statistical comparison (α = 5%).

RESULTS

All instruments had symmetrical blades without radial lands or flat sides, similar surface finishing and an almost equiatomic nickel/titanium ratio, whilst the number of spirals, helical angles and the tip geometry were different. PT Ultimate instruments showed 3 distinct heat treatments that matched with the colour of their metal wire. Slider and ProGlider instruments had similar R-phase start (Rs) and R-phase finish (Rf) temperatures. SX, F1, F2, F3 and Shaper instruments showed equivalent heat treatments (Rs ~45.6°C and Rf ~28.3°C) that were similar to their PT Gold counterparts (Rs ~47.9°C and Rf ~28.2°C), but completely distinct to the PT Universal ones (Rs ~16.2°C and Rf ~-18.2°C). Amongst the PT Ultimate instruments, the lowest maximum torques were observed in the SX (0.44 N cm), Slider (0.45 N cm) and Shaper (0.60 N cm) instruments, whilst the highest was noted in the FXL (4.90 N cm). PT Ultimate Slider and ProGlider had similar torsional (~0.40 N cm) and bending loads (~145.0 gf) (p = 1.000), whilst the other PT Ultimate instruments showed statistically significantly lower maximum torque, higher angle of rotation and lower bending load (higher flexibility) than their counterparts of the PT Universal and PT Gold systems.

CONCLUSIONS

The PT Ultimate system comprises instruments with 3 distinct heat treatments that showed similar phase transformation temperatures to their heat-treated analogues. PT Ultimate instruments presented lower torsional strength and superior flexibility than their counterparts, whilst maximum torque, angle of rotation and bending loads progressively increased with their sizes.

Advancing Nitinol: From heat treatment to surface functionalization for nickel–titanium (NiTi) instruments in endodontics

Nickel-titanium (NiTi) alloy has been extensively researched in endodontics, particularly in cleaning and shaping the root canal system. Research advances have primarily focused on the design, shape, and geometry of the NiTi files as well as metallurgy and mechanical properties. So far, extensive investigations have been made surrounding surface and thermomechanical treatments, however, limited work has been done in the realm of surface functionalization to augment its performance in endodontics. This review summarizes the unique characteristics, current use, and latest developments in thermomechanically treated NiTi endodontic files. It discusses recent improvements in nano-engineering and the possibility of customizing the NiTi file surface for added functionalization. Whilst clinical translation of this technology has yet to be fully realized, future research direction will lie in the use of nanotechnology.

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Nitinol (Nickel Titanium alloy) is widely used to clean/shape root canal system in endodontics.

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To enhance its performance, various thermo-mechanical and nano-engineering modifications have been performed.

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This comprehensive review summarizes the latest advances and future trends relating to functionalized NiTi endodontic files.

Optimum shaping parameters of the middle mesial canal in mandibular first molars: A finite element analysis study

INTRODUCTION

This study investigated the effect of shaping parameters of two different configurations of middle mesial canals (MMC) on the biomechanical behavior and life span of a mandibular first molar using finite element analysis (FEA).

METHODS

A mandibular molar with an independent MMC and another with a confluent MMC were scanned via micro-CT, and FEA models were produced. For each tooth, an intact model and 5 experimental models were produced differed by parameters of how MMC was shaped: unshaped MMC, 25/.04, 25/.06, 30/.04, and 30/.06. Cyclic loading of 50 N was applied on the occlusal surface in vertical and oblique scenarios, and the number of cycles until failure (NCF) was compared to the intact models. In addition, mathematical analyses evaluated the stress distribution patterns and calculated maximum von Mises and maximum principal stresses.

RESULTS

For both the independent and confluent MMC models, shaping the MMC reduced the NCF. The lifelog percentage of models was inversely proportional with radicular shaping parameters during the vertical and oblique loading scenarios. The shaping size of 30/.06 resulted in lower lifelog percentage than the cases with shaping size of 25/.04 in both of the independent and confluent MMC models. For all models, oblique loading reduced NCF more than vertical loading.

CONCLUSION

Shaping the MMC should be kept as conservative as 25/.04. Also, whether the MMC is independent or confluent is a deciding factor in whether to increase the apical diameter or the root canal taper when larger shaping parameters are needed.

Effect from Autoclave Sterilization and Usage on the Fracture Resistance of Heat-Treated Nickel-Titanium Rotary Files

This study aimed to assess the effect of mechanical loading and heating on the cyclic fatigue and torsional fracture resistances of heat-treated nickel-titanium files after usage and autoclaving. Sixty files (One Curve) were tested for cyclic fatigue and torsional fracture resistances using customized devices. The files were divided into three groups according to the test conditions (n = 10); new (group-N), used for simulated canal shaping (group-U), and sterilized after use (group-S). For cyclic fatigue resistances, the files were freely rotated in a curved metal canal under body temperature; the time elapsed to fracture was recorded and the numbers of cycles to fracture (NCF) were calculated. For the torsional resistances, the file tip was fixed and rotated until the file fractured. The maximum torsional load and distortion angle were recorded. The toughness was calculated. Fracture fragments were examined with a scanning electron microscope. Data were analyzed using a one-way analysis of variance and Tukey's post hoc test at the significance level of 95%. Group-U showed significantly higher NCF than group-S (p < 0.05). However, there was no significant differences between groups-N and -S in the NCF (p > 0.05). Group-N showed a significantly bigger distortional angle and higher torsional toughness than groups-U and -S, but the ultimate torsional strength did not have significant difference between the groups. Under the limitation of this study, autoclave sterilization after single-usage did not improve the fracture resistance of heat-treated One Curve nickel-titanium files.

Incidence of Post-Operative Pain following a Single-Visit Pulpectomy in Primary Molars Employing Adaptive, Rotary, and Manual Instrumentation: A Randomized Clinical Trial

Background and Objectives. To differentiate the intensity of postoperative pain after primary molar pulpectomy employing manual instrumentation versus two single-file systems with different kinetics (the XP-Endo shaper file with adaptive instrumentation vs. the Kedo-SG blue file with continuous rotation instrumentation). Materials and Methods. This three-arm, single-blind, randomized clinical trial included assessing 75 healthy children between 4 to 9 years who required pulpectomy for primary molars (mandibular first and second). The three groups each had an equal number of children. Children in Group 1 had their teeth instrumented with the XP-endo Shaper, children in Group 2 had their teeth instrumented with the Kedo-SG Blue file, and children in Group 3 had their teeth instrumented manually using K-files. The degree of postoperative pain was measured using a four-point pain scale at 6-, 12-, 24-, 48-, and 72-h following therapy. Each participant's parent received five flashcards with four faces and a word characterizing each face. The data were analyzed using Kruskal-Wallis and chi-square tests. The level of significance was set to 5%. Results. During the follow-up period, there was a significant difference in postoperative pain intensity between the three groups. The XP-endo shaper was associated with considerably decreased post operative at the 6- and 12-h interval followed by Kedo-SG. The highest post-operative discomfort across the groups was related to the patients who underwent manual instrumentation. Conclusion. In comparison to rotary and manual instrumentation, postoperative pain severity was reduced with adaptive instrumentation.

Design, metallurgy, mechanical properties, and shaping ability of 3 heat-treated reciprocating systems: a multimethod investigation

OBJECTIVE

This study aimed to compare 3 reciprocating systems regarding design, metallurgy, mechanical properties, and shaping ability.

MATERIALS AND METHODS

New Reciproc Blue R25, WaveOne Gold Primary, and REX 25 instruments (n=41 per group) were analyzed regarding design, metallurgy, and mechanical performance, while shaping ability (untouched canal walls, volume of removed dentin, and hard tissue debris) was tested in 36 anatomically matched root canals of mandibular molars. Results were compared using one-way ANOVA post hoc Tukey and Kruskal-Wallis tests with a significant level set at 5%.

RESULTS

All instruments showed symmetrical cross sections with asymmetrical blades, no radial lands, no major defects, and an almost equiatomic nickel and titanium ratio. The highest R-phase start temperatures were observed with WaveOne Gold (46.1°C) and REX (44.8°C), while Reciproc Blue had the lowest R-phase start (34.5°C) and finish (20°C) temperatures. WaveOne Gold had the lowest time to fracture (169 s) and the highest maximum load (301.6 gf) (P <0.05). The maximum torque of Reciproc Blue (2.2 N.cm) and WaveOne Gold (2.1 N.cm) were similar (P >0.05), but lower than REX (2.6 N.cm) (P <0.05). No statistical differences were observed among instruments in the angle of rotation (P >0.05) and in the shaping ability in both mesial and distal canals (P >0.05).

CONCLUSION

Although the overall design, temperature transition phases and mechanical behavior parameters were different among tested instruments, they were similar in terms of shaping ability.

CLINICAL RELEVANCE

All tested heat-treated NiTi reciprocating systems showed similar shaping ability, without clinically significant errors.

Buckling resistance, torque, and force generation during retreatment with D-RaCe, HyFlex Remover, and Mtwo retreatment files

Objectives

This study compared the buckling resistance of 3 nickel-titanium (NiTi) retreatment file systems and the torque/force generated during retreatment.

Materials and Methods

The buckling resistance was compared among the D-RaCe (DR2), HyFlex Remover, and Mtwo R25/05 retreatment systems. J-shaped canals within resin blocks were prepared with ProTaper NEXT X3 and obturated by the single-cone technique with AH Plus. After 4 weeks, 4 mm of gutta-percha in the coronal aspect was removed with Gates-Glidden drills. Retreatment was then performed using DR1 (size 30, 10% taper) followed by DR2 (size 25, 4% taper), HyFlex Remover (size 30, 7% taper), or Mtrwo R25/05 (size 25, 5% taper) (15 specimens in each group). Further apical preparation was performed with WaveOne Gold Primary. The clockwise torque and upward force generated during retreatment were recorded. After retreatment, resin blocks were examined using stereomicroscopy, and the percentage of residual filling material in the canal area was calculated. Data were analyzed using 1-way analysis of variance with the Tukey test.

Results

The HyFlex Remover files exhibited the greatest buckling resistance (p < 0.05), followed by the Mtwo R25/05. The HyFlex Remover and Mtwo R25/05 files generated the highest maximum clockwise torque and upward force, respectively (p < 0.05). The DR1 and DR2 files generated the least upward force and torque (p < 0.05). The percentage of residual filling material after retreatment was not significantly different between file systems (p > 0.05).

Conclusions

NiTi retreatment instruments with higher buckling resistance generated greater clockwise torque and upward force.

Comparative analysis of torsional and cyclic fatigue resistance of ProGlider, WaveOne Gold Glider, and TruNatomy Glider in simulated curved canal

Objectives

This study aimed to compare the torsional and cyclic fatigue resistance of ProGlider (PG), WaveOne Gold Glider (WGG), and TruNatomy Glider (TNG).

Materials and Methods

A total of 15 instruments of each glide path system (n = 15) were used for each test. A custom-made device simulating an angle of 90° and a radius of 5 millimeters was used to assess cyclic fatigue resistance, with calculation of number of cycles to failure. Torsional fatigue resistance was assessed by maximum torque and angle of rotation. Fractured instruments were examined by scanning electron microscopy (SEM). Data were analyzed with Shapiro-Wilk and Kruskal-Wallis tests, and the significance level was set at 5%.

Results

The WGG group showed greater cyclic fatigue resistance than the PG and TNG groups (p < 0.05). In the torsional fatigue test, the TNG group showed a higher angle of rotation, followed by the PG and WGG groups (p < 0.05). The TNG group was superior to the PG group in torsional resistance (p < 0.05). SEM analysis revealed ductile morphology, typical of the 2 fracture modes: cyclic fatigue and torsional fatigue.

Conclusions

Reciprocating WGG instruments showed greater cyclic fatigue resistance, while TNG instruments were better in torsional fatigue resistance. The significance of these findings lies in the identification of the instruments' clinical applicability to guide the choice of the most appropriate instrument and enable the clinician to provide a more predictable glide path preparation.