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.

Opto-magnetic imaging spectroscopy in analyzing rotary NiTi endodontic instruments.

Intra-canal fracture of rotary NiTi instruments occurs due to torsional stress, cyclic fatigue, or a combination of these two factors. Broken instruments are a serious obstacle to shaping, cleaning, and filling of the root canal and can adversely affect the outcome of endodontic therapy. The aim of this study was to examine the magnetic properties and ultrastructural changes of new, used, and fractured NiTi instruments using opto-magnetic imaging spectroscopy (OMIS). The study included three sets of different types of rotary instruments: MTwo (VDW, Munich, Germany), Pro Taper Universal (Dentsply Maillefer, Ballaigues, Switzerland), and BioRace (FKG DENTAIRE Swiss Dental Products, Le Crêt-du-Locle Switzerland). Root canal shaping was performed on root canals with different curvatures, and after intra-canal fracture, instruments of the same type (new, used, and fractured) were analyzed using OMIS at the Faculty of Mechanical Engineering, University of Belgrade. The obtained results showed a coincidence of peak localization for the used instruments that did not suffer a fracture, as well as for new, unused instruments of all examined groups. Additionally, there was a coincidence of peak intensities for new and fractured instruments in all groups. The specific treatment of electropolishing of the active surface of BioRace instruments caused a completely different electromagnetic response compared to conventional NiTi sets of tested instruments. New, unused BioRace instruments had the most pronounced positive (5.6078 n.a.u. x1000) and negative (-8.5218 n.a.u. x1000) intensity values. The analysis of NiTi instruments using opto-magnetic imaging spectroscopy indicated changes in the magnetic properties after their instrumentation.

Combining apical torsional load and cyclic fatigue resistance of NiTi instruments: New approach to determine the effective lifespan of rotary instruments.

In the described proof-of-principle experiments, we introduced a novel testing device to investigate how different concurrent torsional loads influence the cyclic fatigue (CF) resistance of a nickel-titanium (NiTi) instrument. The device was designed to test CF resistance of NiTi files with a standardized load on the apical 5 mm; a movable cylinder controlled by a lever provided a uniform real-time load. Thirty-three NiTi instruments 25.04 (F360, Komet, Lemgo, Germany) were rotated until fracture at 30° curvature under three different torsional loads (n = 11 each); Group A: 2.5 Ncm; Group B: 5 Ncm; Group C: 10 Ncm. anova, multiple comparisons Tamhane tests, regression and Kaplan-Meyer analysis were performed to contrast means. Resistance to cyclic fatigue differed significantly among groups (P = 0.0001). Increased torsional loads led to a decrease in time to failure. An inverse correlation (r = -0.721, P = 0.001) was observed between time and torsional load, with higher torsional loads correlated to shorter times to fracture.

Stereomicroscopic Evaluation of Microcrack Formation in Dentin by ProTaper Next, Revo S, and WaveOne Gold File System.

BACKGROUND: During the biomechanical preparation of the root canal by rotary file systems, stress is generated within the canal, which leads to dentinal microcrack formation. Such defects are evaluated only under the microscope. AIM: The present study aimed to evaluate dentinal microcrack formation after instrumentation with ProTaper Next (M-wire), Revo S (conventional NiTi), and WaveOne Gold (Gold-wire) file systems under the stereomicroscope. MATERIALS AND METHODS: Forty single-rooted teeth free from any defect were selected and divided into four groups (Control, PTN, RS, and WOG). Experimental groups were instrumented with file system used in the study, and the control group were left unprepared. Samples were further decoronated and sectioned at 3 mm, 6 mm, and 9 mm from the apex perpendicular to the long axis and examined under a stereomicroscope at ×25 for different types of microcracks (no fracture, complete fracture, partial fracture, and other fracture). STATISTICAL ANALYSIS USED: Data analysis was done by the Chi-square test using the SPSS version 17.0 software. A two-sided (α = 2) P < 0.05 (P < 0.05) was considered statistically significant. RESULTS: The null hypothesis was rejected. There was a statistically significant difference between the groups. All file systems created microcracks in the root dentin. WOG group showed an incidence of 66.7% for no fracture, PTN group had 40% for other fracture, and RS group had 60% for complete fracture. CONCLUSION: Single file system WOG with gold wire technology proves to be the best choice for canal preparation among the tested groups in terms of least dentinal crack formation.

Análise da resistência à fadiga e resistência à corrosão em instrumentos, HyFlex EDM, HyFlex CM e RaCe / Analysis of fatigue resistance and corrosion resistance in instruments, HyFlex EDM, HyFlex CM and RaCe

O objetivo deste trabalho foi avaliar a resistência à fadiga e a resistência à corrosão em instrumentos endodônticos de NiTi dos sistemas HyFlex EDM, Hyflex CM, e RaCe, além de relacionar estes resultados às características físicas, químicas e estruturais destes instrumentos. Para tal, instrumentos 25/.~ do sistema HyFlex EDM (EDM), instrumentos 30/.06 do sistema HyFlex CM (CM) e RaCe (RC) foram utilizados. A composição química foi determinada por espectroscopia dispersiva de raios-X, as fases presentes nos materiais foram determinadas por difratometria de raios-X (DRX) e as temperaturas de transformação de fases por calorimetria exploratória diferencial (DSC). A análise da rugosidade superficial dos instrumentos foi realizada por microscopia de força atômica (AFM) e a caracterização dimensional dos instrumentos foi realizada através da mensuração do diâmetro a 3mm da ponta. Ensaios de fadiga até a ruptura foram realizados nos três grupos (n=10) e o tempo médio até a fratura determinado. Instrumentos novos foram subdivididos em grupos controle e experimental para cada sistema. Os grupos experimentais foram submetidos à ensaios de fadiga, até 3/4 do tempo médio para a ruptura e posteriormente a testes de corrosão (potencial de circuito aberto e polarização). Os grupos controle foram diretamente submetidos aos mesmos testes de corrosão. A análise de Weibull foi aplicada para avaliação da probabilidade de falha em relação ao tempo nos instrumentos testados em fadiga até a ruptura. Análise de variância com índice de significância de 0,05% foi adotada para os resultados de composição química, temperatura de transformação de fases, diâmetro, rugosidade e testes de corrosão. A composição química foi praticamente equiatomica em instrumentos RaCe, com presença de Níquel e Titânio. Já instrumentos EDM e CM apresentaram, além destes elementos, Oxigênio na composição. A caracterização estrutural evidenciou maiores temperaturas de transformação de fase Af (austenite finish) para os grupos tratados termicamente (CM e EDM), este dado foi comprovado pelos resultados da difratometria de raios-X com a presença de fase-R e austenita (fase ß) à temperatura ambiente para ambos. O grupo RC, apresentou menores temperaturas Af (p<.05), além de apenas austenita na análise por DRX. As medidas de diâmetro apresentaram-se sem diferenças estatisticamente significativas entre os grupos CM e RC, ambos significativamente maiores que EDM. Os testes de fadiga flexural apresentaram tempo até a fratura sem diferença entre EDM e CM (p>0,05) e ambos foram superiores em relação à RC (p<0.05). Por outro lado, a análise de Weibull apresentou melhores parâmetros de confiabilidade para RC e CM. Os ensaios de corrosão apresentaram diferenças significativas entre os sistemas analisados, mas não entre instrumentos novos e ciclados. Os grupos CM apresentaram maior resistência à corrosão, seguido de EDM e RC. A rugosidade superficial foi maior em instrumentos CM, seguidos de EDM e RC. De acordo com os resultados a microestrutura dos instrumentos tratados termicamente melhora a resistência à fadiga e resistência à corrosão, independentemente do tipo de usinagem.

The aim of this study was to assess the fatigue and corrosion resistance of NiTi endodontic instruments. HyFlex EDM 25 /. ~, HyFlex CM 30/.06 and RaCe 30/.06 were used. Chemical composition was determined by energy-dispersive X-ray spectroscopy, phase constitution by X-ray diffraction and transformation temperatures by differential scanning calorimetry. Surface roughness was analyzed by atomic microscopic force (AFM) and the geometric characterization of the instruments was performed by measuring the diameter at 3mm from the tip. Initially, 10 instruments from each group were tested until rupture in the flexural fatigue bench to obtain the mean time until fracture. Then, new instruments were subdivided into control and experimental groups for each system. Experimental groups were subjected to fatigue tests, up to 3/4 of the mean time to rupture and subsequently to corrosion tests. Control groups were directly subjected to the same corrosion tests. Weibull analysis was applied to assess the reliability in the tested instruments to failure. Analysis of variance with a significance of 0.05% was adopted for the results of chemical composition, phase transformation temperature, diameter, roughness, and corrosion tests. The chemical composition was near equiatomic in RaCe instruments, with the presence of Nickel and Titanium. On the other hand, EDM and CM instruments presented, in addition to these elements, Oxygen in the composition. The structural characterization showed higher Af phase transformation temperatures (austenite finish) for the heat-treated groups (CM and EDM), this data was confirmed by the results of X-ray diffractometry with the presence of R-phase and austenite (phase ß) at room temperature for both. The RC group had lower temperatures Af (p<.05), in addition to only austenite in the XRD analysis. Diameter measurements showed no statistically significant differences between the CM and RC groups, both significantly larger than EDM. Flexural fatigue tests showed time to fracture with no difference between EDM and CM (p>0.05) and both were superior to RC (p<0.05). However, the Weibull analysis showed better reliability parameters for RC and CM. The corrosion tests showed significant differences between the analyzed systems, but not between new and cycled instruments. The CM groups showed greater resistance to corrosion, followed by EDM and RC. Surface roughness was higher in CM instruments, followed by EDM and RC. According to the results, the microstructure of the thermally treated instruments improves fatigue resistance and corrosion resistance, regardless of the type of machining.

Comparison of the cyclic fatigue resistance of VDW.ROTATE, TruNatomy, 2Shape, and HyFlex CM nickel-titanium rotary files at body temperature.

OBJECTIVES: This study aims to compare the cyclic fatigue resistance of VDW.ROTATE, TruNatomy, 2Shape, and HyFlex CM nickel-titanium (NiTi) rotary files at body temperature. MATERIALS AND METHODS: In total, 80 VDW.ROTATE (25/0.04), TruNatomy (26/0.04), 2Shape (25/0.04), and HyFlex CM (25/0.04) NiTi rotary files (n = 20 in each group) were subjected to static cyclic fatigue testing at body temperature (37°C) in stainless-steel artificial canals prepared according to the size and taper of the instruments until fracture occurred. The number of cycles to fracture (NCF) was calculated, and the lengths of the fractured fragments were measured. The data were statistically analyzed using a 1-way analysis of variance and post hoc Tamhane tests at the 5% significance level (p < 0.05). RESULTS: There were significant differences in the cyclic fatigue resistance among the groups (p < 0.05), with the highest to lowest NCF values of the files as follows: VDW.ROTATE, HyFlex CM, 2Shape, and TruNatomy. There was no significant difference in the lengths of the fractured fragments among the groups. The scanning electron microscope images of the files revealed typical characteristics of fracture due to cyclic fatigue. CONCLUSIONS: The VDW.ROTATE files had the highest cyclic fatigue resistance, and the TruNatomy and 2Shape files had the lowest cyclic fatigue resistance in artificial canals at body temperature.

Secondary Root Canal Treatment with Reciproc Blue and K-File: Radiographic and ESEM-EDX Analysis of Dentin and Root Canal Filling Remnants.

Secondary root canal treatment requires the complete removal of filling materials with different chemical-physical properties. A newly developed single-use NiTi instrument (Reciproc Blue, RB) may be more effective in root canal retreatment. The aim of the present study was to evaluate morphology and composition of remnants after retreatment with RB compared to traditional K-File technique, in canals obturated with Thermafil/AH Plus. Twenty-four single-rooted human teeth were shaped with NiTi obturated with AH-Plus/Thermafil and retreated using RB NiTi instruments or manual K-Files. Radiographs were taken to evaluate endodontic space and radiopacity of residual filling-material before/after procedures. After retreatment, samples were longitudinally split and observed by environmental scanning electron microscopy connected to energy dispersive X-Ray spectroscopy (ESEM-EDX) to analyze the debris/remnant position, microchemistry, and dentinal surface morphology. Time for retreatments was recorded and compared using one-way ANOVA (p-value = 0.05). Radiopaque filling residuals were found in both groups. RB system resulted statistically faster than manual K-File in retreatment procedure (p < 0.001). Root canal space radiographic appearance obtained after retreatment with RB was wider than K-File (p < 0.05). ESEM-EDX revealed 4 different morphological dentin area. Area-1: debris-free with typical Ca, P, and N composition of dentin and detected in 70% of the surface. Area-2: presence of deproteinized smear layer free from N and debris in 15% of the surface. Area-3: a thick packed smear layer N-free and with fine debris consisting of trace elements from sealer in 10% of the surface. Area-4: packed with debris and trace elements. No difference was observed between both instruments regarding root canal space appearance and ESEM-EDX analysis. Both systems were able to remove filling material but created a dentine morphology composed of packed debris and filling materials embedded into the smear layer. Dentin surface composition resulted in collagen depleted by irrigation procedures. The reciprocating system required less time to complete retreatment.

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

OBJECTIVES: This systematic review evaluated the influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) instruments. MATERIALS AND METHODS: A systematic search without restrictions was conducted in the following electronic databases: PubMed, Scopus, Web of Science, ScienceDirect, Cochrane, and Open Grey. The hand search was also performed in the main endodontic journals. The eligible studies were submitted to the methodological assessment and data extraction. RESULTS: From 203 abstracts, a total of 10 articles matched the eligible criteria. After reading the full articles, 2 were excluded because of the absence of the heat-treated instruments in the experimental design and 3 due to the lack of a control group using heat-treated instruments without autoclave sterilization. From the 5 included studies, 1 presented a low risk of bias, 3 presented moderate and 1 high risk. It was observed heterogeneous findings in the included studies, with autoclave sterilization cycles increasing, decreasing or not affecting the cyclic fatigue life of heat-treated NiTi instruments. However, the retrieved studies evaluating the cyclic fatigue resistance of endodontic instruments presented different protocols and assessing outcomes, this variability makes the findings less comparable within and also between groups and preclude the establishment of an unbiased scientific evidence base. CONCLUSIONS: Considering the little scientific evidence and considerable risk of bias, it is still possible to conclude that autoclave sterilization procedures appear to influence the cyclic fatigue resistance of heat-treated NiTi instruments.

Comparison of the cyclic fatigue resistance of hyflex EDM, vortex blue, protaper gold, and onecurve nickel-Titanium instruments.

OBJECTIVE: This in vitro study aimed to compare the cyclic fatigue resistance of HyFlex EDM (HEDM), Vortex Blue (VB), ProTaper Gold (PG), and OneCurve (OC) nickel-titanium (NiTi) instruments. MATERIALS AND METHODS: About 12 HEDM (25/.~), 12 VB (25/.06), 12 PG (25/.08), and 12°C (25/.06) instruments were included in this study. All the instruments were tested with a 60° angle of curvature and a 3-mm radius of curvature. All the instruments were utilized until fracture occurred, and then the number of cycles to failure (NCF) was calculated. The data were analyzed statistically using Kruskal-Wallis H and Mann-Whitney U-tests. The statistical significance level was set at P < 0.05. RESULTS: HEDM instruments had the highest cyclic fatigue resistance among all the other instruments (P < 0.05). The OC instruments had a significantly higher fatigue resistance than the PG and VB instruments (P < 0.05); however, there was no significant difference between PG and VB instruments in the NCF (P > 0.05). CONCLUSION: Within the limitations of this in vitro study, it was found that the cyclic fatigue resistance was higher for the HEDM instruments than for the VB, PG, and OC instruments.

Comparative Analysis of Dentinal Crack Formation Following Root Canal Instrumentation with Hand K-Flex Files, ProTaper Next, and Self-adjusting Files.

AIM: To evaluate and compare in vitro the dentinal crack formation in root canal dentin after root canal instrumentation with hand K-Flex files, ProTaper Next, and self-adjusting engine-driven files. MATERIALS AND METHODS: Ninety-two human mandibular first molar teeth were randomly divided into four groups (n = 23) as per the instrumentation protocol: group I-unprepared teeth (control); group II-hand K-Flex files (Sybron Endo); group III-ProTaper Next X1 and X2 (Dentsply Maillefer); group IV-self-adjusting file (ReDent Nova, Israel). All the roots were sectioned perpendicular to the long axis of the tooth at 9 mm, 6 mm, and 3 mm from the apex and thereby obtaining sixty-nine samples, which were then subjected to a stereomicroscopic examination for detection of dentinal cracks. Statistical analyses were done using the Chi-square test with SPSS (version 19), and p value was set at p < 0.05. RESULTS: Statistically significant differences were seen between the instrumented groups. No dentinal cracks were found in the unprepared roots and those prepared with hand K-Flex files (0/23). Self-adjusting-file-instrumented group showed significantly less incidence of crack formation when compared to the ProTaper Next group with p = 0.001. CONCLUSION: Self-adjusting file is an efficient engine-driven NiTi instrument for root canal instrumentation with the least occurrence of crack formation in the root canal dentin compared to the ProTaper Next system. CLINICAL SIGNIFICANCE: The introduction of NiTi rotary file systems has metamorphosed the endodontic treatment by their better cutting efficiency and cleaning potentiality. Yet, evidenced-based clinical studies are to be conducted on the incidence of microfractures that can lead to vertical root fractures, which will be produced irrespective of the motion kinematics and design feature and thereby compromising the clinical maintenance of the endodontically treated teeth.

Evaluation of Flexibility, Microstructure and Elemental Analysis of Some Contemporary Nickel-Titanium Rotary Instruments.

BACKGROUND: Contemporary nickel-titanium (NiTi) rotary endodontic instruments had a revolutionary impact on the success of root canal treatment. AIM: To evaluate the flexibility, microstructure and elemental analysis of four different recent NiTi rotary instruments, namely; Wave One Gold, TF adaptive, HyFlex EDM and Gr_Reciproc Blue compared to conventional Protaper Universal (F2). MATERIAL AND METHODS: The NiTi rotary files were subjected to cantilever bending test to evaluate their flexibility. The microstructural characteristics and elemental analysis were examined via scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX). RESULTS: The TF adaptive, HyFlex EDM and Wave One Gold endodontic files showed significantly lower cantilever bending values (i.e., higher flexibility) than Protaper F2 and Gr_Reciproc Blue (p < 0.05). The SEM micrographs showed that the bulk of all examined files showed multiple striations due to the cutting process, on the other hand, their external surfaces were different: The Protaper Universal F2 showed multiple voids, while the TF Adaptive surface exhibited more uniform structure. The Hyflex EDM had a crater-like surface, whereas Wave one Gold showed machining grooves with minimum defects, while Reciproc Blue displayed machining grooves with random scratch lines. There was a significant difference in bulk and surface elemental analysis of the various examined files, yet composed mainly of the same elements. CONCLUSION: Chemical composition, heat treatment, manufacturing process and geometrical design of the NiTi rotary instrument have a great influence on their flexibility and microstructure.

Diameter and Taper Variability of Single-file Instrumentation Systems and Their Corresponding Gutta-percha Cones.

INTRODUCTION: Manufacturers offer single-file instrumentation systems with matching gutta-percha (GP) cones to simplify root canal preparation and obturation. The purpose of this study was to determine whether file diameters and tapers match with corresponding cone diameters and tapers (precision) as well as industry standards (accuracy). METHODS: Twenty files and corresponding GP cones from each size of F360 (#25, #35, #45, #55 with .04 taper) and Reciproc (#25, #40, #50 with variable tapers) instruments were examined by using optical microscopy (×32) to determine their diameter and taper. Precision was evaluated by using one-way analysis of variance (α = 0.05) with Scheffé post hoc tests and t tests with Bonferroni correction. Accuracy was calculated by subtracting the nominal values from the measured values of all files and GP cones, and mean diameter and taper differences were compared by using one-way analysis of variance (α = 0.05) and Scheffé post hoc test for pairwise comparison. RESULTS: For F360, the majority of file and cone diameters were within the tolerance levels, but most of the file diameters were significantly larger than GP cone diameters (P < .05), but the majority of all measured values were within the tolerance levels. For Reciproc, file and cone diameters at D1 and D3 mostly approached the nominal values. At the coronal end, file diameters #25 and #50 were significantly smaller than cone diameters (P < .05). For both instrumentation systems, almost all file and cone tapers matched with the preset tolerance ranges. For Reciproc, significant differences between file and GP cone demonstrated either smaller cone or smaller file diameters and tapers, depending on the size. Most of the measured values were within the acceptable range, but diameters at the coronal end exhibited the highest percent difference from the nominal values. CONCLUSIONS: Despite the call for standardization, variability in diameter and taper dimensions between single-file instrumentation systems and their corresponding GP cones can be expected.

Defect propagation in NiTi rotary instruments: a noncontact optical profilometry analysis.

AIM: To evaluate the presence and propagation of defects and their effects on surfaces of nickel-titanium (NiTi) instruments using noncontact, three-dimensional optical profilometry, and to assess the accuracy of this method of investigation. METHODOLOGY: The flute surface areas of instruments from two commercial instrumentation systems, namely Reciproc R25 (n = 5) and WaveOne Primary (n = 5), were assessed and compared before and after performing two instrumentation cycles in simulated root canals in clear resin blocks. All the analyses were conducted on areas measuring 211 × 211 µm, located 3 mm from the tips of the instruments. A quantitative analysis was conducted before and after the first and second instrumentation cycles, using the Sa (average roughness over the measurement field), Sq (root mean square roughness) and Sz (average height over the measurement field) amplitude parameters. All the data were submitted to statistical analysis at a 5% level of significance. RESULTS: There was a significant increase (P = 0.007) in wear in both groups, especially between baseline and the second instrumentation cycle, with significantly higher wear values being observed on WaveOne instruments (Sz median values = 33.68 and 2.89 µm, respectively, for WO and RP groups). A significant increase in surface roughness (P = 0.016 and P = 0.008, respectively, for Sa and Sq) was observed in both groups from the first to the second instrumentation cycle, mostly in WaveOne specimens. Qualitative analysis revealed a greater number of defects on the flute topography of all the instruments after use. CONCLUSIONS: More defects were identified in WaveOne Primary instruments compared to Reciproc R25, irrespective of the evaluation stage. The investigation method provided an accurate, repeatable and reproducible assessment of NiTi instruments at different time-points.

The incidence of dentinal cracks during root canal preparations with reciprocating single-file and rotary-file systems: A meta-analysis.

As a dangerous factor in vertical root fracture, dentinal crack formation is often associated with root canal instruments. We conducted this meta-analysis to compare the influence of two types of nickel titanium (NiTi) instruments that have different movements (reciprocating single-file versus full-sequence rotary file systems) on dentinal cracks formation during root canal preparation. Searches were conducted in PubMed, ISI Web of Knowledge, Embase and Cochrane Library using a combination of keywords. Titles and abstracts of all articles were independently assessed by two reviewers in accordance with the predefined inclusion criteria. Relevant studies were acquired in full-text form. Data in these articles were independently extracted. A meta-analysis was conducted using Review Manager 5.3. The results showed that the WaveOne and Reciproc files with a reciprocating motion produced significantly fewer dentinal cracks than the conventional rotational ProTaper technique.

Correlação do diâmetro do preparo de uma nova geração de instrumentos de NiTi com as dimensões de cones de guta-percha de sua antiga geração através de uma análise morfométrica / Correlation of the diameter preparation of a new generation of NiTi instrument with the dimensions of gutta-percha points of its old generation through a morphometric analysis

Objetivo: O presente trabalho teve o objetivo de determinar as dimensões e verificar se os instrumentos X1, X2 e X3 atendem as recomendações da norma ANSI/ ADA nº 101 e se os cones de guta-percha F1, F2 e F3 atendem a norma ANSI/ADA nº 78. Material e Métodos: Os resultados dos instrumentos foram comparados com as dimensões dos cones de guta-percha. Foram utilizados 10 instrumentos e 10 cones de cada tipo. As imagens para análise micromorfométrica foram obtidas com uma lupa Opticam e as medidas determinadas com o software TSView versão 7.2.1.7. Os diâmetros em D3, D6 e D9 reais foram comparados com os nominais pelo teste t-student. Os diâmetros dos instrumentos em D3, D6 e D9 foram comparados com os dos cones pelo teste Anova e complementados com teste de comparações múltiplas SNK. Todos os testes adotaram nível de significância α=5%. Resultados: Os resultados obtidos mostraram que há diferença estatisticamente significante entre as dimensões reais e nominais dos instrumentos (p < 0,05). O instrumento X3 apresentou diferença estatisticamente significante em relação ao cone F1 (p < 0,05), onde os valores do cone são menores do que os dos instrumentos. Conclusão: Dentro das limitações deste estudo pôde-se concluir que: os instrumentos X1 e os cones de guta-percha não atenderam as recomendações de suas normas. O cone F1 pode ser uma opção para obturação dos canais modelados com o instrumento X3, porém a termoplastificação se faz necessária.

Objective: The aim of the present study was to verify if the Protaper Next instruments X1, X2, and X3 and the Protaper Universal gutta-percha cones F1, F2, and F3 meet the ANSI/ADA 101 and 78 recommendations. Material and Methods: The instruments' dimensions were compared with those obtained by the gutta-percha cones. For this, ten instruments and ten cones of each type were used. Micromorphometric images were obtained and analyzed through a stereomicroscope (OptiCam) and measurements were obtained with TSView software, version 7.2.1.7. The D3, D6, and D9 diameters were compared with the nominal diameters using the Student's t-test. After this, the real diameters of the instruments D3, D6, and D9 were compared with the gutta-percha cone diameters by Anova supplemented with SNK test for multiple comparisons. A p ≤0.05 was considered significant. Results: The results showed statistically significant differences between the real diameter and nominal diameter of the instruments (p <0.05). The X3 instrument showed a statistically significant difference when compared to the F1 cone (p <0.05), and the cone values were lower than the instrument values. Conclusion: Within the limitations of this study, it can be concluded that: 1) the X1 instrument and the gutta-percha points did not meet the recommendations, and 2) the F1 cone can be an option for filling the modeled channels with the X3 instrument, but termoplastification is required.

Cutting efficiency of nickel-titanium rotary and reciprocating instruments after prolonged use.

The aim of the present study was to compare the cutting efficiency of Twisted File instruments used in continuous rotation or TF Adaptive motion and evaluate if prolonged use significantly affected their cutting ability. 20 new NiTi instruments were used in the present study (TF tip size 35, 0.06 taper; Sybron-Endo, Orange, CA, USA), divided into 2 subgroups of 10 instruments each, depending on which movement was selected on the endodontic motor. Group 1: TF instruments were activated using the program TF continuous rotation at 500 rpm and torque set at 2 N; Group 2: TF instruments were activated using the reciprocating TF Adaptive motion. Cutting efficiency was tested in a device developed to test the cutting ability of endodontic instruments. Each instrument cut 10 plastic blocks (10 uses) and the length of the surface cut in a plastic block after 1 min was measured in a computerized program with a precision of 0.1 mm. Maximum penetration depth was calculated after 1 use and after 10 uses, and mean and standard deviation (SD) of each group was calculated. Data were statistically analyzed with a one-way ANOVA test (P < 0.05). TF instruments used in continuous rotation (Group 1) cut a mean depth of 10.4 mm (SD = 0.6 mm) after the first use and 10.1 mm (SD 1.1 mm) after 10 uses, while TF instruments used with the Adaptive motion cut a mean depth of 9.9 mm (SD = 0.7 mm) after the first use and 9.6 mm (SD = 0.9 mm) after 10 uses. There was no statistically significant difference between the two groups investigated (P > 0.05) nor between instruments after 1 or 10 uses. In conclusion, the TFA motion showed a lateral cutting ability similar to continuous rotation and all tested instruments exhibited the same cutting ability after prolonged use.

Constant Insertion Rate Methodology for Measuring Torque and Apical Force in 3 Nickel-Titanium Instruments with Different Cross-sectional Designs.

INTRODUCTION: The aim of this study was to evaluate the cutting characteristics of 3 nickel-titanium instruments with different cross-sectional designs using a recently developed methodology. METHODS: Insertion tests at a constant rate of 5.4 mm/min were performed on a bench test device by measuring the torque and apical force required for penetrating prefabricated acrylic blocks containing an artificial canal preflared with #10 and #15 K-files. Size 20/.06 Mtwo (VDW, Munich, Germany) and RaCe (FKG, La-Chaux De Fonds, Switzerland) instruments, together with ProTaper Universal (PTU) F1 instruments (Dentsply Maillefer, Ballaigues, Switzerland) (10 instruments of each type), were tested using an endodontic motor set at 300 rpm and 5 N·cm. The instruments were characterized with respect to the pitch length, rake angle, and cross-sectional area. Statistical analysis was performed with analysis of variance (α = 0.05). RESULTS: The torque was significantly lower for Mtwo compared with the other 2 groups (P < .05). It was also lower for RaCe in comparison with PTU F1 (P < .05). Regarding the apical force, the RaCe instruments had lower values when compared with the Mtwo and PTU F1 instruments (P < .05). There was no statistically significant difference between the PTU F1 and Mtwo instruments (P > .05). CONCLUSIONS: The methodology allowed the cutting properties of the instruments to be assessed in terms of their different geometric characteristics. The cross-sectional design, especially in Mtwo instruments with 2 sharp edges and great chip removal capability, was a differential factor for their higher cutting action.

Effect of Different Instrumentation Techniques on Vertical Root Fracture Resistance of Endodontically Treated Teeth.

STATEMENT OF THE PROBLEM: Vertical root fractures are catastrophic events that often result in tooth extraction. Many contributing factor are associated with increasing incidence of vertical root fracture. Root canal preparation is one of the predisposing factors which can increase the root susceptibility to vertical fracture. PURPOSE: The aim of this study was to compare the effects of three different instrumentation techniques on vertical root fracture resistance of endodontically treated teeth. MATERIALS AND METHODS: In this study, 120 freshly extracted mandibular premolar teeth of similar dimensions were decoronated and randomly divided into control (n=30), nickel-titanium hand K-file (HF, n=30), BioRaCe rotary file (BR, n=30), and WaveOne reciprocating single-file (WO, n=30) groups. After cleaning and shaping the root canals, AH26 was used as canal sealer, and obturation was completed using the continuous wave technique. The root canals were embedded vertically in standardised autopolymerising acrylic resin blocks, and subjected to a vertical load to cause vertical root fracture. The forces required to induce fractures were measured using a universal testing machine. ANOVA and Tukey's post-hoc test were used to analyse the data. RESULTS: All experimental groups showed statistically significant reductions in fracture resistance as compared with the control group. There was a statistically significant difference between the HF and BR groups. The WO group did not differ significantly from the HF group or the BR group. CONCLUSION: All three instrumentation techniques caused weakening of the structure of the roots, and rendered them susceptible to fracture under lesser load than unprepared roots. The fracture resistance of roots prepared with the single-file reciprocating technique was similar to that of those prepared with NiTi hand and rotary instrumentation techniques.

Stereomicroscopic evaluation of dentinal defects induced by new rotary system: "ProTaper NEXT".

INTRODUCTION: The objective of this study was to evaluate dentinal defects formed by new rotary system - Protaper next™ (PTN). MATERIALS AND METHODS: Sixty single-rooted premolars were selected. All specimens were decoronated and divided into four groups, each group having 15 specimens. Group I specimens were prepared by Hand K-files (Mani), Group II with ProTaper Universal (PT; Dentsply Maillefer), Group III with Hero Shaper (HS; Micro-Mega, Besancon, France), and Group IV with PTN (Dentsply Maillefer). Roots of each specimen were sectioned at 3, 6, and 9mm from the apex and were then viewed under a stereomicroscope to evaluate presence or absence of dentinal defects. RESULTS: In roots prepared with hand files (HFs) showed lowest percentage of dentinal defects (6.7%); whereas in roots prepared with PT, HS, and PTN it was 40, 66.7, and 26.7%, respectively. There was significant difference between the HS group and the PTN group (P < 0.05). CONCLUSION: All rotary files induced defects in root dentin, whereas the hand instruments induced minimal defects.

Cyclic fatigue resistance of 3 different nickel-titanium reciprocating instruments in artificial canals.

INTRODUCTION: The purpose of this study was to evaluate the cyclic fatigue resistance of 3 different nickel-titanium reciprocating instruments. METHODS: A total of 45 nickel-titanium instruments were tested and divided into 3 experimental groups (n = 15): group 1, WaveOne Primary instruments; group 2, Reciproc R25 instruments; and group 3, Twisted File (TF) Adaptive M-L1 instruments. The instruments were then subjected to cyclic fatigue test on a static model consisting of a metal block with a simulated canal with 60° angle of curvature and a 5-mm radius of curvature. WaveOne Primary, Reciproc R25, and TF Adaptive instruments were activated by using their proprietary movements, WaveOne ALL, Reciproc ALL, and TF Adaptive, respectively. All instruments were activated until fracture occurred, and the time to fracture was recorded visually for each file with a 1/100-second chronometer. Mean number of cycles to failure and standard deviations were calculated for each group, and data were statistically analyzed (P < .05). Instruments were also observed through scanning electron microscopy to evaluate type of fracture. RESULTS: Cyclic fatigue resistance of Reciproc R25 and TF Adaptive M-L1 was significantly higher than that of WaveOne Primary (P = .009 and P = .002, respectively). The results showed no statistically significant difference between TF Adaptive M-L1 and Reciproc R25 (P = .686). Analysis of the fractured portion under scanning electron microscopy indicated that all instruments showed morphologic characteristics of ductile fracture that were due to accumulation of metal fatigue. CONCLUSIONS: No statistically significant differences were found between the instruments tested except for WaveOne Primary, which showed the lowest resistance to cyclic fatigue.