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.

Mechanical Stress Decreases the Amplitude of Twisting and Bending Fluctuations of Actin Filaments.

A variety of biological roles of mechanical forces have been proposed in cell biology, such as cell signaling pathways for survival, development, growth, and differentiation. Mechanical forces alter the mechanical conditions within cells and their environment, which strongly influences the reorganization of the actin cytoskeleton. Single-molecule imaging studies of actin filaments have led to the hypothesis that the actin filament acts as a mechanosensor; e.g., increases in actin filament tension alter their conformation and affinity for regulatory proteins. However, our understanding of the molecular mechanisms underlying how tension modulates the mechanical behavior of a single actin filament is still incomplete. In this study, a direct measurement of the twisting and bending of a fluorescently labeled single actin filament under different tension levels by force application (0.8-3.4 pN) was performed using single-molecule fluorescence polarization (SMFP) microscopy. The results showed that the amplitude of twisting and bending fluctuations of a single actin filament decreased with increasing tension. Electron micrograph analysis of tensed filaments also revealed that the fluctuations in the crossover length of actin filaments decreased with increasing filament tension. Possible molecular mechanisms underlying these results involving the binding of actin-binding proteins, such as cofilin, to the filament are discussed.

BlueShaper: un nuevo sistema multialeación para la instrumentación mecanizada en endodoncia: comunicación breve / BlueShaper: a new multialloy system for mechanized instrumentation in endodontics: brief communication

El objetivo de esta comunicación es describir y analizar el sistema BlueShaper para la preparación quirúrgica mecaniza- da de los conductos radiculares. El sistema dispone de un set básico de 4 limas: Z1, Z2, Z3 y Z4, con un D0 de 0,14 mm, 0,17 mm, 0,19 mm y 0,25 mm respectivamente y conicidad variable que oscila entre el 2 y 10 %. La lima Z1 posee una aleación Pink, que le confiere mayor resistencia a la torsión y una gran capacidad de corte. Las limas Z2, Z3 y Z4 presentan una aleación Blue que aumenta la resistencia a la fatiga cíclica e incrementa su flexibilidad. Para conductos radiculares más amplios se incluyen, además, las limas Z5, Z6 y Z7. La empresa comer- cializa conos de gutapercha BlueShaper que se corresponden con las limas Z3, Z4, Z5, Z6 y Z7. El sistema de limas mul- tialeación Blue Shaper podría considerarse como un nuevo aporte clínico para la preparación mecánica de los conductos radiculares (AU)

The aim of this communication was to describe and analyze the BlueShaper system for the mechanized surgical preparation of root canals. The system has a basic set of 4 files: Z1, Z2, Z3 and Z4, with 0.14 mm, 0.17 mm, 0.19 mm and 0.25 mm DO respective- ly, and variable conicity ranging between 2 and 10 %. Z1 file has a Pink alloy, which gives it greater resistance to torsion and great cutting capacity. The Z2, Z3 and Z4 files feature a Blue alloy that increases resistance to cyclic fatigue and increases their flexibility. For larger root canals, the Z5, Z6 and Z7 files are also included. The company supplies specific BlueShaper ́s gutta-percha cones for Z3, Z4, Z5, Z6 and Z7 files. The BlueShaper multialloy file system could be consid- ered as a new clinical contribution for the mechanical prepa- ration of root canals (AU)

Probing local lateral forces of focal adhesions and cell-cell junctions of living cells by torsional force spectroscopy.

The number and strength of mechanical connections of cells to their local environment can be indicative of their migration and invasion potential. Gaining direct access to the mechanical properties of individual connections and bringing them into a relationship with the state of disease, however, is a formidable task. Here, we present a method to directly sense focal adhesions and cell-cell contacts with a force sensor to quantify the lateral forces of their anchoring points. We found local lateral forces of 1.0-1.5 nN for focal adhesions and slightly higher values at the interfaces between cells where cell-cell contacts are located. Interestingly, a modified surface layer was observed exhibiting considerably reduced tip friction directly next to the area of a retracting cell edge on the substrate. We expect that this technique can improve the understanding of the relationship between mechanical properties of cell connections and the pathological state of cells in the future.

Influence of temperature on the torsional properties of two thermally treated NiTi rotary instruments.

This study aimed to evaluate the influence of temperature on torsional strength and angular deflection of two experimental NiTi rotary instruments manufactured from Blue and Gold thermal treatments and with identical cross-sections. A total of 40 experimental NiTi instruments 25.06 and with a triangular cross-section and manufactured from Blue and Gold thermal treatments were used (n=20). The torsional test was performed in the 3 mm from the tip of the instrument according to ISO 3630-1. The torsional test evaluated the torsional strength and angular deflection to failure at room temperature (21°C ± 1° C) and body temperature (36°C ±1°C). The fractured surface of each fragment was observed by using scanning electron microscopy (SEM). Data were analyzed using an unpaired t test for inter and intra-group comparison and the level of significance was set at 5%. The results showed that the body temperature did not affect the torsional strength and angular deflection of the instruments when compared with room temperature (P>0.05). However, at body temperature, the Blue NiTi instruments presented significantly lower angular deflection in comparison with Gold NiTi instruments (P<0.05). There was no significant difference regarding the torsional strength of the instruments at body temperature (P>0.05). The temperature did not affect the torsional strength of the instruments manufactured from Blue and Gold technology. However, the Blue NiTi instruments presented significantly lower angular deflection than Gold instruments at 36°C temperature.

Comparison of mechanical resistance and standardisation between original brand and replica-like endodontic systems.

This study compared the original (ProTaper Next and Reciproc) endodontic systems with their replica-like brands (X File and Only One File) in terms of standardisation, design, phase-transformation behaviour, composition and mechanical behaviour. X File showed greater taper values than ProTaper Next, while Only One File had the greatest tip diameter. Both replica-like files had an active tip and greater dimensions than their reports. There were also significant differences between the original and replica-like systems in terms of their phase-transformation behaviour and the precision of the measurement lines. Only One File showed significantly lower cyclic fatigue and torsional resistance than Reciproc (p < 0.05). There were no significant differences in the cyclic fatigue, torsional resistance and composition of NiTi between X File and ProTaper Next (p > 0.05). Although replica systems show mechanical properties that can be acceptable, they are not consistent in terms of standardisation and design.

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.

Comparação entre Reciproc Blue e quatro instrumentos réplicas: aspectos metalúrgicos, geometria, comportamento em torção e flexão / Comparison between Reciproc Blue and four replicalike instruments: metallurgical aspects, geometry, and behavior in torsion and flexion

A introdução da liga NiTi na endodontia proporcionou a fabricação de instrumentos com excelentes propriedades mecânicas, e uma das principais características é a possibilidade de alteração das temperaturas de transformação da liga, o qual pode possibilitar a presença de martensita em temperatura ambiente e consequentemente um efeito memória de forma. Entretanto, alguns dos sistemas comercializados atualmente possuem pouca ou nenhuma informação científica relatando suas propriedades mecânicas, características de design e métodos de fabricação. O objetivo deste trabalho foi comparar características geométricas, metalúrgicas e propriedades mecânicas (resistência à torção e flexão) de instrumentos Reciproc Blue (VDW, Munique, Alemanha), e quatro sistemas reciprocantes réplicas. Um total de 39 instrumentos de cada um dos sistemas reciprocantes, Reciproc Blue (RB), Prodesign R (PDR), V File (VF), V+ File (V+) e Univy One (UO) foram utilizados na pesquisa. O programa de Image J foi utilizado para mensuração dos diâmetros a cada milímetro da parte ativa e da área da seção transversal a 3 mm da ponta dos instrumentos. Imagens de MEV da parte ativa foram realizados para avaliar o acabamento superficial dos instrumentos. A composição atômica, fases presentes e temperaturas de transformação foram verificadas através de EDS, DRX e DSC, respectivamente. A flexibilidade foi aferida através de ensaios de dobramento até 45º conforme a especificação ISO 3630-1, e os ensaios de resistência à torção foram realizados de acordo com a especificação Nº28 ANSI/ADA. Todos os instrumentos apresentaram uma quantidade aproximadamente equiatômica de níquel e titânio. A análise qualitativa das fases cristalinas realizada através de ensaios de DRX, demonstrou a predominância de Fase R em todos os grupos, com exceção do grupo UO que apresenta uma mistura de fase R e martensita B19'. Na avaliação da área da seção, o instrumento RB obteve valores intermediários, os instrumentos PDR e V+ possuem menores valores e os instrumentos VF e UO possuem maiores valores. Observou-se grande impacto da geometria sobre as propriedades mecânicas, sendo que aqueles sistemas que apresentavam menor área que RB (PDR, V+) mostraram-se mais flexíveis e menos resistentes à torção (p<0.05), e o instrumento VF que teve maior área apresentou, como esperado, menos flexibilidade (p<0.05) e resistência torcional semelhante (p>0.05). A única exceção se deu com o sistema UO, que embora apresentasse uma maior área de seção, mostrou-se mais flexível e menos resistente à torção, provavelmente por influência da maior quantidade de martensita presente à temperatura ambiente. Nenhum dos instrumentos réplicas avaliados apresentaram características e comportamento mecânico iguais ao sistema padrão RB. Sugere-se que mais estudos devem ser realizados para a comparação do comportamento clínico destes instrumentos.

The introduction of NiTi alloy in endodontics has allowed the manufacturing of instruments with excellent mechanical properties, and one of the main characteristics is the ability to change alloy's transformation temperature, which can enable the presence of martensite at room temperature and consequently favor a shape memory effect. However, some of the currently marketed systems have limited or no scientific information regarding their mechanical properties, design characteristics, and manufacturing methods. The aim of this study was to compare the geometric characteristics, metallurgical aspects, and mechanical properties (torsional and flexural strength) of Reciproc Blue instruments (VDW, Munich, Germany) with four replica-like reciprocating systems. A total amount of 39 instruments from each reciprocating system, namely Reciproc Blue (RB), Prodesign R (PDR), V File (VF), V+ File (V+), and Univy One (UO), were used in the study. The Image J program was used to measure the diameters at every millimeter along the instruments active portion and the cross-sectional area at 3 mm from the instrument tip. SEM images of the active portion were obtained to evaluate the surface finishing of the instruments. Atomic composition, phases present, and transformation temperatures were determined through EDS, XRD, and DSC analyses, respectively. Flexibility was assessed by bending tests up to 45° according to ISO 3630-1 specifications, and torsional strength tests were performed according with ANSI/ADA Specification No. 28. All instruments exhibited an approximately equiatomic composition of nickel and titanium. Qualitative analysis of the crystalline phases using XRD tests demonstrated the predominance of the R-phase in all groups, except for the UO group, which exhibited a mixture of Rphase and B19' martensite. In terms of diameter and cross-sectional area evaluation, the RB instrument obtained intermediate values, while the PDR and V+ instruments had smaller values, and the VF and UO instruments had larger values. A significant impact of geometry on mechanical properties was observed, with systems exhibiting a smaller area than RB (PDR, V+) being more flexible and less torsion-resistant (p<0.05), and the VF instrument with a larger area showed, as expected, less flexibility (p<0.05) and similar torsional resistance (p>0.05). The only exception was the UO system, which, despite having a larger geometric configuration, exhibited greater flexibility and less torsional resistance, likely due to the higher amount of martensite present at room temperature. None of the replica-like instruments evaluated showed identical characteristics and mechanical behavior to the standard RB system. Further studies are suggested to compare the clinical performance of these instruments.

Effect of nickel-titanium alloys on root canal preparation and on mechanical properties of rotary instruments.

The aim of this study was to evaluate the quality of curved root canal preparation, torsional fatigue, and cyclic fatigue of rotary systems manufactured with different NiTi alloys. Ninety single-rooted canals with curvatures of 15° to 30o were scanned and divided into three groups according to the rotary system used: BT-Race (BTR) - 10.06, 35.00, 35.04; SequenceRotaryFile (SRF) - 15.04, 25.06, 35.04; and ProDesignLogic (PDL) - 25.01, 25.06, 35.05. Each system was used on three specimens. The teeth were prepared, scanned, and analyzed to assess increase in volume, transportation, and centering ability of the root canal. Torsional fatigue of glide path instruments (BTR 10.06, SRF 15.04 and PDL 25.01) and cyclic fatigue of the finishing instrument (BTR 35.04, SRF 35.04 and PDL 35.05) were obtained by analyzing completely new instruments (n = 10) and instruments after they had been used three times (n = 10). After the torsional and cyclic fatigue tests, the fractured surface of the new and used instruments were examined by scanning electron microscopy. Increase in volume, canal transportation, and centering ability showed no significant differences among the groups (p > 0.05). The torsional test showed that SRF 15.04 produced the highest torque values for both new and used instruments, followed by PDL 25.01 and BTR 10.06 (p < 0.05). PDL 25.01, both new and used, exhibited higher values of angular deflection followed by SRF 15.04 and BTR 10.06 (p < 0.05). As regards cyclic fatigue, use of PDL 35.05, both new and used, required a longer time and larger number of cycles than did SRF 35.04 and BTR 35.04 (p < 0.05). Clinical use affected the torsional fatigue of BTR; however, cyclic fatigue was not significantly affected (p < 0.05). All rotary systems were able to prepare the curved canals satisfactorily and were used safely on the three specimens. Relative to torsional fatigue, SRF 15.04 exhibited a higher torque, and PDL 25.01, higher angular deflection. BTR 10.06 was the most affected by clinical use. PDL 35.05 showed greater resistance to cyclic fatigue.

What Meaningful Information Are the Instruments Mechanical Testing Giving Us? A Comprehensive Review.

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

Device for Torsional Fatigue Strength Assessment Adapted for Pulsating Testing Machines.

The torsional fatigue test determines the fatigue limit for a certain asymmetry coefficient of the cycle. The assessment of fatigue tests is performed on specialized machines. There are two types of torsion testing machines: universal machines that have the torsion component and specialized machines only for torsion testing. Nevertheless, no matter which proposed option we choose, the purchase prices for these testing machines or the values spent for self-management are quite high. This paper presented a device used for torsion fatigue testing, adaptable to a universal pulsating testing machine, designed to determine the torsion fatigue limit for different materials. The built device is simple and reliable, and therefore inexpensive. By using this device, we can determine the limit of the torsional fatigue after any stress cycle and we can use the parameters obtained from the universal machine to which it was attached. The torque and twisting angle of the test specimen during the test can be determined by calculation. The paper also presented an experimental method for determining shear strains based on calibration experiment, using a specimen on which strain gauges were mounted. The values taken from this calibration experiment were compared with those obtained from the theoretical calculation.

Evaluation of Torsional Resistance and Bending Stiffness of Coronal Flaring Nickel-Titanium Instruments.

OBJECTIVE: The aim of this study was to evaluate the bending and torsional resistance of the following instruments: Mtwo 25/.07 (MT - VDW, Munich, Germany), Navigator W-XN 25.07 (WXN - Wizard Navigator, Medin, Nové Mesto na Morave, Czech Republic), ProTaper Universal SX 19/.04 (PSX - Dentsply Tulsa Dental Specialties, Tulsa, USA), MK Orifice Shapper 17/.08 (OS - MK Life Medical and Dental Products, Porto Alegre, Brazil) and MK Sequence 17.12 (MKS - MK Life Medical and Dental Products, Porto Alegre, Brazil). METHODS: One hundred instruments were used (n=20). Resistance to bending (n=10), torque and angular deflection (n=10) at the failure of new instruments were measured according to ISO 3630-1. Metal mass volume at 3 mm from the tip was evaluated using micro-computed tomography (micro-CT). The fractured surface of each fragment was examined by scanning electron microscopy (SEM). Data were analysed using 1-way analysis of variance and Tukey tests. RESULTS: Torsional resistance values of MK Sequence were higher than the other groups (P<0.05). No differences were observed among MT, WXN and OS (P>0.05) and PTS, which presented the lowest values (P<0.05). MT showed the highest angular deflection (P<0.05). WXN and PSX presented no significant difference (P>0.05). PSX and OS also showed no significant differences (P>0.05). MKS instruments had the lowest angular deflection values (P<0.05). There were significant differences among all the groups in bending stiffness test (P<0.05), but PSX had the lowest torque to bend (P<0.05). MKS had the larger metal mass volume at 3 mm from the tip (P<0.05). SEM analysis showed similar and typical features of torsional failure for all instruments tested. CONCLUSION: In conclusion, MK Sequence 17/.12 had the highest torsional fracture resistance. Mtwo 25/.07 showed higher angular deflection capacity, and ProTaper Universal SX the 19/.04 lower bending stiffness.

Resistencia de diferentes implantes y componentes sometidos a sobre torque. Estudio in-vitro / Resistance of different implants and components subjected to high torque. An in vitro study

Objetivo: Describir las fallas en diferentes sistemas de implantes al ser sometidos a fuerzas de torsión creciente, de- terminar el torque en el cual aparece un daño medible en el implante o alguno de sus componentes y especificar la falla más frecuente. Materiales y métodos: Se realizó un estudio experi- mental in vitro. Se utilizaron 88 implantes agrupados según diseño y marca comercial (Federa, Rosterdent, Biomet 3i, Tree-Oss, B&W, ML) en 11 grupos de 8 implantes cada uno. Éstos fueron inmovilizados en acrílico y fijados en una pren- sa. Se aplicó una fuerza de torsión creciente con torquímetro de precisión digital hasta la aparición de alguna falla en el implante o sus componentes. Se registró el torque en el que se produjo la falla. Se realizó estadística descriptiva para el análisis de datos. Resultados: El 100% de los implantes o alguno de sus componentes mostraron una falla detectable al ser sometidos a fuerzas de torsión creciente (rango de torque: 83,5 Ncm ­im- plante con conexión cono morse 8 grados­ a 384 Ncm ­implan- te de conexión interna sin montar­). El torque promedio más bajo en el que aparecieron los daños fue 103,75 (±8,08) Ncm para implantes de conexión interna tipo cono morse, mientras que el más alto fue 279,87 (±89,73) Ncm para implantes de conexión interna sin montar. La falla más frecuente (28,4%) fue la fractura del tornillo del portaimplante y falseo del hexá- gono externo simultáneamente. Conclusión: Las fallas detectables a fuerzas de torsión creciente ocurrieron entre 83,5 Ncm y 384 Ncm. La falla rei-terada fue la fractura del tornillo del portaimplante y falseo del hexágono simultáneamente (AU)

Aim: To describe the failures in different implant sys- tems when subjected to increasing torsional forces, deter- mine the torque at which measurable damage occurs to the implant or one of its components, and determine the most frequent failure. Materials and methods: This was an experimental in vitro study. A total 88 implants were used, grouped accord- ing to design and trademark (Federa, Rosterdent, Biomet 3i, Tree-Oss, B&W, ML) into 11 groups of 8 implants each. The implants were immobilized in Duralay acrylic and fixed in a vice. Increasing torsional force was applied with a digital pre- cision torque wrench until the occurrence of any failure in the implants or their components. The torque at which the failure occurred was recorded. Descriptive statistics were performed for data analysis. Results: 100% of the implants or any of their compo- nents showed a detectable failure when subjected to increas- ing torsional forces (force range: 83.5 Ncm in an implant with 8-degree Morse taper connection to 384 Ncm in an implant with unmounted internal connection). The lowest average torque at which damage occurred was 103.75 (±8.08) Ncm for conical implants with Morse internal connection, while the highest was 279.87 (±89.73) Ncm for implant with unmounted internal connection. The most frequent failure (28.4%) was fracture of the implant retaining screw and distortion of the external hexagon simultaneously (AU)

A comparative biomechanical study of the Distal Tibia Nail against compression plating for the osteosynthesis of supramalleolar corrective osteotomies.

The Distal Tibia Nail (DTN; Mizuho, Japan) has demonstrated higher biomechanical stiffness to locking plates in previous research for A3 distal tibia fractures. It is here investigated as a fixation option for supramalleolar corrective osteotomies (SMOT). Sixteen Sawbones tibiae were implanted with either a DTN (n = 8) or Medial Distal Tibia Plate (MDTP; n = 8) and a SMOT simulated. Two surgical outcome scenarios were envisaged: "best-case" representing an intact lateral cortex, and "worst-case" representing a fractured lateral cortex. All samples were subjected to compressive (350 N, 700 N) and torsional (± 4 Nm, ± 8 Nm) testing. Samples were evaluated using calculated construct stiffness from force-displacement data, interfragmentary movement and Von Mises' strain distribution. The DTN demonstrated a greater compressive stiffness for the best-case surgical scenario, whereas the MDTP showed higher stiffness (p < 0.05) for the worst-case surgical scenario. In torsional testing, the DTN proved more resistant to torsion in the worst-case surgical setup (p < 0.05) for both ± 4 Nm and ± 8 Nm. The equivalent stiffness of the DTN against the MDTP supports the use of this implant for SMOT fixation and should be considered as a treatment option particularly in patients presenting vascularisation problems where the MDTP is an inappropriate choice.

Evaluation of Design, Metallurgy, Microhardness, and Mechanical Properties of Glide Path Instruments: A Multimethod Approach.

INTRODUCTION: This study aims to compare the design, metallurgy, microhardness, and mechanical properties of 3 glide path nickel-titanium (NiTi) instruments. METHODS: A total of 132 ProGlider (Dentsply Sirona, Ballaigues, Switzerland), Edge Glide Path (EdgeEndo, Johnson City, TN), and R-Pilot instruments (VDW, Munich, Germany) (44 per group) were selected. Design was assessed through stereomicroscopy (blades, helical angle, measuring lines, and deformation) and scanning electron microscopy (symmetry, cross section, tip, and surface finishing). NiTi ratios were measured by energy-dispersive X-ray spectroscopy and phase transformation temperatures by differential scanning calorimetry. Microhardness and mechanical performance (torsion, bending, and buckling resistance tests) were also evaluated. Statistical analyses were performed with the Mood median test with a significance set at 5%. RESULTS: The Edge Glide Path had the lowest number of blades and the R-Pilot the greatest helical angle. All instruments had an almost equiatomic NiTi ratio, while showing different cross sections and tip geometries. The Edge Glide Path had a smoother surface finishing. The R-Pilot showed martensitic characteristics at room temperature, whereas mixed austenite plus R-phase was observed in the other instruments. The R-Pilot had higher results on the microhardness (436.8 hardness Vickers number), maximum torsion (0.9 Ncm), and buckling load (0.7 N) tests (P < .05), whereas the Edge Glide Path had a superior angle of rotation (683.5°) and the ProGlider was more flexible (144.1 gf) (P < .05). CONCLUSIONS: Differences in the design of the instruments and the phase transformation temperatures accounted for their mechanical behavior. The R-Pilot showed the highest torque, buckling, and microhardness, whereas the ProGlider instrument was the most flexible.

Nickel-Titanium Rotary Instruments: An In Vitro Comparison (Torsional Resistance of Two Heat-treated Reciprocating Files).

AIM AND OBJECTIVE: The present study aims to evaluate the difference in torsional resistance of two reciprocating nickel-titanium (Ni-Ti) rotary files: WaveOne Gold and EdgeOne Fire. MATERIALS AND METHODS: A total of 40 nickel-titanium rotary instruments (n = 40): 20 WaveOne Gold Small (WOGS) and 20 EdgeOne Fire Small (EOFS) were divided into two groups. Each instrument was tested using a torsional resistance device already validated in previous studies to evaluate and compare torsional resistance. The static torsional test was implemented by blocking each instrument at 3 mm from the tip and rotating it until fracture with a reciprocating motion. Torque to fracture (TtF) and fragment length (FL) were measured and statistically analyzed. RESULTS: Statistical analysis of TtF found significant differences between the two groups (p<0.05). The EOFS showed higher TtF if compared to WOGS, with a mean value and a standard deviation of 3.05 ± 0.07 (N cm) against 2.97 ± 0.08 (N cm). Data for FL showed no significant differences (p>0.05) between the two groups. CONCLUSION: According to the results of this study, it is reasonable to assert that EOFS instruments showed a higher torsional resistance if compared to the WOGS. CLINICAL SIGNIFICANCE: As evidenced by this study, EOFS should be considered as a safer solution, in terms of torsional resistance, if compared to WOGS, reducing the risk of intracanal separation due to excessive torsional load.

Incidence of Different Types of Intracanal Fracture of Nickel-Titanium Rotary Instruments: A Systematic Review.

AIM: The aim of this systemic review is to investigate these parameters by analyzing the characteristics of fractured instruments to determine which is the most relevant mechanical stress that induces intracanal separation in vivo. BACKGROUND: The fracture of nickel-titanium (Ni-Ti) instruments is a result of flexural fatigue and torsional fatigue. An electronic search was conducted in MEDLINE database, Web of Science, and Cochrane following preferred reporting items for systematic reviews and meta-analyses guidelines. Data were collected and the key features from the included studies were extracted. Overview quality assessment questionnaire scoring assessed the quality of the articles. A total of 12 articles were selected, where the lowest score was 13. REVIEW RESULTS: Considering Ni-Ti rotary instruments, this overall evaluation comprehends 939 broken instruments with an incidence of fracture of 5%. Out of the 12 selected articles, 10 studies revealed that flexural failure was the predominant mode (range of 62-92%). It appears that motion plays an important role when it comes to mechanisms of fracture. The majority of defects found in hand-operated instruments were in the form of torsional failure. Although the major cause of separation of rotary instruments is flexural fatigue, smaller instruments show more torsional fracture than the larger instruments. The average fragment length was found to be 2.5 mm and 3.35 mm, respectively, for torsional failure and flexural failure. The risk of bias depends on fractographic analysis. CONCLUSION: Flexural fatigue is the predominant mode of fracture in rotary Ni-Ti instruments. The type of motion and size of the instrument seem to affect the mechanism of fracture. Fragment length may show a strong association with the type of fracture mechanism. CLINICAL SIGNIFICANCE: This systemic review found that flexural fatigue is the most relevant mechanical stress that induces intracanal separation in vivo. Moreover, in clinical practice, the fragment length might be an excellent indicator of the type of fracture.

FtsZ induces membrane deformations via torsional stress upon GTP hydrolysis.

FtsZ is a key component in bacterial cell division, being the primary protein of the presumably contractile Z ring. In vivo and in vitro, it shows two distinctive features that could so far, however, not be mechanistically linked: self-organization into directionally treadmilling vortices on solid supported membranes, and shape deformation of flexible liposomes. In cells, circumferential treadmilling of FtsZ was shown to recruit septum-building enzymes, but an active force production remains elusive. To gain mechanistic understanding of FtsZ dependent membrane deformations and constriction, we design an in vitro assay based on soft lipid tubes pulled from FtsZ decorated giant lipid vesicles (GUVs) by optical tweezers. FtsZ filaments actively transform these tubes into spring-like structures, where GTPase activity promotes spring compression. Operating the optical tweezers in lateral vibration mode and assigning spring constants to FtsZ coated tubes, the directional forces that FtsZ-YFP-mts rings exert upon GTP hydrolysis can be estimated to be in the pN range. They are sufficient to induce membrane budding with constricting necks on both, giant vesicles and E.coli cells devoid of their cell walls. We hypothesize that these forces result from torsional stress in a GTPase activity dependent manner.

A Paradigm Shift for Torsional Stiffness of Nickel-Titanium Rotary Instruments: A Finite Element Analysis.

INTRODUCTION: The aim of this study was to investigate the influence of mass and the polar moment of inertia on the torsional behavior of nickel-titanium rotary instruments to understand which parameter of cross-sectional design had a key role in terms of torsional resistance. METHODS: Four different instrument models were designed and meshed using computer-aided engineering software (SolidWorks; Dassault Systems, Waltham, MA). Instrument models shared the same characteristics, except for cross-sectional design; triangle, rectangle, square, and hollow square geometry was selected. Finite element analysis was performed simulating a static torsional test using the FEEPlus internal solver (Solid Works). Von Mises stress and torsional load at fracture were calculated by the software. Linear regression analysis was performed to investigate the relationship of the polar moment of inertia, cross-sectional area, inner core radius, and mass per volume on the torsional resistance of nickel-titanium rotary instruments. RESULTS: The polar moment of inertia positively affected the maximum torsional load with the highest level of correlation (R2 = 0.917). It could be stated that the higher the polar moment of inertia is, the more maximum torsional load at fracture is present. Mass and cross-sectional area had a lower level of correlation compared with the polar moment of inertia (R2 = 0.5533). According to this, 2 instruments with the same mass/mm and/or cross-sectional area could have different torsional resistance. CONCLUSIONS: The polar moment of inertia can be considered as the most important cross-sectional factor in determining the torsional resistance of rotary instruments over metal mass and cross-sectional area.

Comparison of the Torsional Resistance of 4 Different Glide Path Instruments.

INTRODUCTION: The present study aimed to compare the torsional strength of the initial files of the Mtwo (VDW, Munich, Germany) and novel Rotate systems (VDW, Munich, Germany) with the ProGlider (Dentsply Sirona, Ballaigues, Switzerland) and R-Pilot (VDW) glide path instruments. METHODS: The Mtwo (10/.04), ProGlider (16/.02), R-Pilot (12.5/.04), and Rotate (15/.04) glide path files were compared regarding their torsional strength, which was tested using a specially designed test device (N = 20). The data obtained were statistically analyzed at 5% significance level using 1-way analysis of variance and the post hoc Tukey test. The fragment surfaces and separated instruments were examined with ×50, ×100, and ×1000 magnification under a scanning electron microscope. RESULTS: The R-Pilot group showed the highest torsional strength value among all groups (P < .05), whereas there was no significant difference between the torsional strength values of the Mtwo and ProGlider groups (P > .05). The Rotate group had the lowest torsional strength among all groups (P < .05). The Mtwo group showed the lowest angle of rotation among all groups (P < .05). CONCLUSIONS: Although the R-Pilot glide path file exhibited the highest torsional strength in all groups, Rotate showed the highest angle of rotation. Differences in torsional resistance of the instruments may be associated with their manufacturing methods and design features.