Quantitative and Qualitative Elemental Analysis of Different Nickel–Titanium Rotary Instruments by Using Scanning Electron Microscopy and Energy Dispersive Spectroscopy

Effects of Side Flattening on Torsional and Cyclic Fracture Resistance of Nickel-Titanium File

INTRODUCTION

The purpose of this study was to evaluate the effect of side flattening of cutting flutes on the cyclic resistance and torsional resistance of nickel-titanium files.

METHODS

Both novel flattened Platinum V.EU (PL) and standard nonflattened CC Premium V.EU (CC) rotaries were tested. For cyclic fatigue tests, all the files were rotated in an artificial root canal with a curvature of 45° and a radius of 6.06 mm at 300 rpm (n = 15 in each group). The number of cycles to failure (NCF) was calculated. For torsional tests, the files were rotated at 2 rpm clockwise until fracture occurred. The maximum torque value at fracture was measured and the toughness and distortion angle were computed. Subsequently, 5 fragments were randomly selected in each experiment, the cross-section and longitudinal direction of the fragments were photographed using a scanning electron microscope. An unpaired t-test was performed at a significance level of 95%.

RESULTS

There was a statistically significant difference in NCF between CC and PL (P < .05). CC showed higher NCF than PL. There was no statistically significant difference between CC and PL with regards to the parameters related to torsional resistance (distortion angle, ultimate strength, and toughness) (P > .05).

CONCLUSION

Within the limitations of this study, side flattening of the file did not improve cyclic resistance or torsional resistance of the files. As side flattening may reduce a file's cyclic resistance, such files should be used with caution in clinical practice.

Comparison of cyclic fatigue resistance of Rotate instrument with reciprocating and continuous rotary nickel-titanium instruments at body temperature in relation to their transformation temperatures

OBJECTIVE

The aim of this study was to compare the cyclic fatigue resistance at body temperature and phase transformation behaviors of novel Rotate instrument (25.06) with rotating Mtwo (25.06) and reciprocating Reciproc Blue (25.08) and Reciproc (25.08) instruments.

MATERIALS AND METHODS

The Rotate, Reciproc Blue, Reciproc, and Mtwo instruments free of visible deformations were collected and tested in a static cyclic fatigue test method, which has a ceramic block containing an artificial canal with 60° angle of curvature and a 5-mm radius of curvature at 37 °C (n = 16). All instruments were operated until fracture occurred, and both time to fracture (TF) and the lengths of the fractured fragments were recorded. TF data was analyzed with one-way ANOVA followed by post hoc Tukey tests and Weibull analysis, and fractured fragment length data were subjected to one-way ANOVA and post hoc Tukey tests (P < 0.05). Two unused instruments from each brand were also subjected to differential scanning calorimetry (DSC) analysis to determine their phase transformation temperatures.

RESULTS

The Reciproc Blue instruments showed significantly higher TF values and reliability than the other groups (P < 0.05). Rotate instruments exhibited greater cyclic fatigue resistance than the Reciproc and Mtwo instruments (P < 0.05). No significant difference was detected among the fractured fragment lengths (P > 0.05). The lowest austenite finish temperature was exhibited by the Mtwo, which presented a single transformation peak, followed by the Rotate, Reciproc Blue, and Reciproc instruments which all presented two peaks during transformation.

CONCLUSIONS

Cyclic fatigue resistance of instruments manufactured from thermally treated Blue wire instruments was superior to those of the Mtwo and Reciproc, whereas reciprocating the Blue wire showed the highest resistance.

CLINICAL RELEVANCE

The present study compared the cyclic fatigue resistance of the novel Rotate instrument with similar instruments manufactured from conventional nickel-titanium, m-wire, and Blue wire at body temperature and reported that Blue-treated instruments exhibited superior cyclic fatigue resistance.

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.

Torsional resistance of three ProTaper rotary systems

BACKGROUND

The aim of this study is to compare the torsional resistance of the available ProTaper rotary systems, namely, ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG).

METHODS

A total of 195 files from the three systems distributed into 13 groups (PTU-S1, PTU-S2, PTU-F1, PTU-F2, PTU-F3, PTG-S1, PTG-S2, PTG-F1, PTG-F2, PTG-F3, PTN-X1, PTN-X2 and PTN-X3) were subjected to torsional fatigue until failure. The torsional test was performed according to ISO 3630-1, where each file was placed in a straight position to eliminate the influence of cyclic fatigue. The Kruskal-Wallis test was conducted to compare the mean maximum torques and angular deflections at fracture for the groups, and the Mann-Whitney test was performed for pairwise comparisons. The significance level was set at 0.05 and the fractured surfaces were examined under a scanning electron microscope.

RESULT

Among the tested files, PTG-S1 had the lowest torsional fatigue resistance, whereas PTU-F2 and PTU-F3 had the highest torsional resistance. The scanning electron microscope showed typical features of torsional failure.

CONCLUSION

The new ProTaper systems (PTG and PTN) did not show improved torsional resistance in comparison with PTU.

Mechanism of fracture of NiTi superelastic endodontic rotary instruments

The aim is to investigate the premature catastrophic fracture produced for different periods during clinical endodontic treatment of two brands of NiTi endodontic rotary instruments. 3 samples as-received, 6 samples used with patients for 2 and 7 h and 5 samples fractured were studied for each brand of endodontic NiTi rotary instruments. Transformation temperatures (M_s, M_f, A_s and A_f) and enthalpies of transformation were determined by calorimetry. Critical stresses until fracture (σ^β→SIM, σ^SIM→β) were obtained using an electromechanical testing machine. The samples were also visualized by Scanning Electron Microscopy. Calorimetric studies have shown an increase of the M_s and A_s transformation temperatures with time of use as well as a decrease of their stress transformations. Moreover, reverse transformation enthalpies decreased along the time. The enthalpies of transformation decreased because martensitic plates were anchored, which prevented their transformation to austenite; thus losing its superelastic effect. The stabilisation of the martensitic plates induced the collapse of the structure and so the main cause for the fracture. The heat treatment proposed has been increased the life in service of NiTi superelastic endodontic instruments recovering theirs superelastic effect.

Sulfate-Reducing Bacteria: Biofilm Formation and Corrosive Activity in Endodontic Files

AIM

This study describes the biofilm formation and the corrosive capacity of sulfate-reducing bacteria (SRB) on the metallic structure of used endodontic files.

METHODS

Sulfate-reducing bacteria (SRB) (Desulfovibrio desulfuricans oral and Desulfovibrio fairfieldensis or D. desulfuricans environmental) were inoculated into the culture media (Postgate C culture medium or modified Postgate E culture medium). The biocorrosive potential of these bacteria will be an important component of a biopharmaceutical under development called BACCOR. Afterwards, four used endodontic files (UEFs) were separately inoculated into a specific culture media for 445 days at 30°C in an incubator. The four UEFs were placed in a scanning electron microscope (SEM) and analyzed by the energy-dispersive X-ray spectrometry (EDS).

RESULTS

The confocal laser scanning microscopic images indicate the presence of biofilm in the four samples. The SEM and SEM-EDS revealed the presence of rough, irregular structures adhering along the metallic surface of the used endodontic files, suggesting a mature calcified biofilm with a high concentration of Ca, P, C, and S.

CONCLUSION

The formation of SRB biofilms on used endodontic files shows characteristics that may contribute to the biocorrosion of these files, and the results may also provide complementary data for a biopharmaceutical, which is still under development to assist in the removal of fractured endodontic files inside root channels.

Cyclic fatigue resistance, torsional resistance, and metallurgical characteristics of M3 Rotary and M3 Pro Gold NiTi files

Objectives

To evaluate the mechanical properties and metallurgical characteristics of the M3 Rotary and M3 Pro Gold files (United Dental).

Materials and Methods

One hundred and sixty new M3 Rotary and M3 Pro Gold files (sizes 20/0.04 and 25/0.04) were used. Torque and angle of rotation at failure (n = 20) were measured according to ISO 3630-1. Cyclic fatigue resistance was tested by measuring the number of cycles to failure in an artificial stainless steel canal (60° angle of curvature and a 5-mm radius). The metallurgical characteristics were investigated by differential scanning calorimetry. Data were analyzed using analysis of variance and the Student-Newman-Keuls test.

Results

Comparing the same size of the 2 different instruments, cyclic fatigue resistance was significantly higher in the M3 Pro Gold files than in the M3 Rotary files (p < 0.001). No significant difference was observed between the files in the maximum torque load, while a significantly higher angular rotation to fracture was observed for M3 Pro Gold (p < 0.05). In the DSC analysis, the M3 Pro Gold files showed one prominent peak on the heating curve and 2 prominent peaks on the cooling curve. In contrast, the M3 Rotary files showed 1 small peak on the heating curve and 1 small peak on the cooling curve.

Conclusions

The M3 Pro Gold files showed greater flexibility and angular rotation than the M3 Rotary files, without decrement of their torque resistance. The superior flexibility of M3 Pro Gold files can be attributed to their martensite phase.

Evolution of Nickel-titanium Alloys in Endodontics

To improve clinical use of nickel-titanium (NiTi) endodontic rotary instruments by better understanding the alloys that compose them. A large number of engine-driven NiTi shaping instruments already exists on the market and newer generations are being introduced regularly. While emphasis is being put on design and technique, manufacturers are more discreet about alloy characteristics that dictate instrument behavior. Along with design and technique, alloy characteristics of endodontic instruments is one of the main variables affecting clinical performance. Modification in NiTi alloys is numerous and may yield improvements, but also drawbacks. Martensitic instruments seem to display better cyclic fatigue properties at the expense of surface hardness, prompting the need for surface treatments. On the contrary, such surface treatments may improve cutting efficiency but are detrimental to the gain in cyclic fatigue resistance. Although the design of the instrument is vital, it should in no way cloud the importance of the properties of the alloy and how they influence the clinical behavior of NiTi instruments.

CLINICAL SIGNIFICANCE

Dentists are mostly clinicians rather than engineers. With the advances in instrumentation design and alloys, they have an obligation to deal more intimately with engineering consideration to not only take advantage of their possibilities but also acknowledge their limitations.

Fracture of nickel titanium rotary instrument during root canal treatment and re-treatment: a 5-year retrospective study

AIM

To evaluate retrospectively the incidence of K3 nickel titanium rotary instrument fracture in referred cases during root canal treatment and re-treatment.

METHODOLOGY

Clinical and radiographic reports of 12 867 endodontic cases treated at the King Abdulaziz medical city between January 2010 and November 2015 were reviewed to obtain information on intracanal fractured instruments with respect to the treatment performed, tooth type and the size and at what level the instrument fractured (coronal, middle or apical). The degree of canal curvature was classified into mild (<10^° ), moderate (10-25^° ) or severe (>25^° ). Logistic regression was used to test the incidence of instrument fracture in relation to the root canal treatment performed and tooth type. Chi-square tests were used to analyse the fracture incidence in the treated teeth in respect to fracture level and fractured file diameter. The level of significance was set at 0.05.

RESULTS

Root canal treatment was performed on 8946 cases, whilst re-treatment was performed on 3921 cases. The fracture incidence was higher during re-treatment cases (2.96%) than in primary root canal treatment (0.74%) (P < 0.001) with a 1.41% incidence overall. There was a trend for more fractures in maxillary (1.68%) and mandibular (1.35%) molar teeth. Moreover, 56.6% of the fractured instruments occurred in severely curved canals, and the apical third of the root canal was the most common site for instrument fracture (85.7%), followed by middle (13.2%), and coronal (1.1%) thirds, mostly with file sizes 20 and 25 (59.9% and 25.27%, respectively).

CONCLUSION

The fracture incidence of K3 instruments was significantly greater during root canal re-treatment than root canal treatment, mainly with small instruments and in the apical third of the canals.

Analysis of Surface Characteristics of ProTaper Universal and ProTaper Next Instruments by Scanning Electron Microscopy

Background

Many new rotary files systems have been introduced, however, limited research has been conducted related to the surface irregularities of these files and if these have any effects on the files themselves. Hence, the aim of the present study was to analyze surface irregularities of the ProTaper® Universal rotary files (PTU) and the ProTaper Next™ rotary files (PTN) before and after instrumentation in curved canals. The main objective was to investigate the nature of these irregularities and how they might influence the use and fracture of rotary files during root-canal treatments.

Material and Methods

The files were examined pre-operatively using a stereomicroscope and scanning electron microscopy(SEM) to analyze surface imperfections and the presence of particles. Mesial roots of forty extracted mandibular molars were selected. Each instrument was used to prepare one of the mesial canals. The files were then rinsed with alcohol, and autoclaved and analyzed again.

Results

Of the 80 files used in this study, five files fractured, five files unwound and seven files were curved or bent and they all belonged to the PTU group. Irregularities and debris could be visualized with the SEM on both unused PTU and PTN files. Most of the debris was found associated with deeper milling grooves and defects on the surface of the metal. Surface analysis of the files that were used and sterilized were performed and the SEM images demonstrated organic debris, metal flash, and crack formation and initiation of fractures for both file types. All files showed machining grooves, metal flash, debris, and defects on cutting edges.

Conclusions

These irregularities appear to be critical in the accumulation of debris and initiation of fatigue and crack propagation within the NiTi alloy. The accumulation of debris could be a concern due to the potential exchange of organic debris between patients.

Key words:ProTaper® Universal, ProTaper Next™, surface characteristics, SEM.

Assessment of root canal enlargement using Mtwo and BioRace rotary files

Objective. To evaluate root canal enlargement following mechanical shaping using 2 nickel titanium rotary systems. Material and Methods. Forty single-rooted teeth were immersed in resin and sectioned perpendicular to the long axis at 4, 8, and 12 mm from the apex. Digital capture of sections was performed before and after canal instrumentation using Mtwo and BioRace instruments. The area increase of endodontic space was calculated by subtraction. Results. The use of both instruments has allowed the removal of great amounts of dentin from the canal walls, even when the endodontic morphology is characterized by awkwardness to reach recesses. Conclusions. Both procedures seem to be valid and no differences were found between Mtwo and BioRaCe considering the amount of dentin removed at different distances from the apex.

Qualitative analysis of files of four different rotary systems, before and after being used for the twelfth time

The aim of this study was to make a comparative evaluation of the surface topography of the cervical third and tip of four different rotary systems, before and after being used 12 times, in resin blocks with simulated root canals with standardized 45° curvatures, and analyzed by scanning electronic microscopy (SEM). A total of 1,440 resin blocks with simulated root canals and standardized curvatures were used. The blocks were divided into four groups and prepared by the crown down technique according to the manufacturers' recommendations: Group 1 (G1)--K3®, Group 2 (G2)--Protaper Universal®, Group 3 (G3)--Twisted Files®, and Group 4 (G4)--Biorace®. After each preparation, the instruments were washed and autoclaved. A total of 24 instruments were selected, being three new instruments and three after having been used for the 12th time, from each group. These instruments were analyzed by SEM. To perform the evaluation, 24 micrographs were observed by 12 evaluators who attributed a score to the images according to a template. In the qualitative analysis of the cervical region and tip of new instruments, it was observe that the files of Groups G4 and G2 were the least rough and those of G1, the roughest. In the same manner, the cervical region of the instruments was qualitatively analyzed after the 12th time of using them, and there was no statistically significant difference at a level of 1% (ANOVA P < 0.01) between G2 and G4 as well as between G1 and G3. As regards the tip, it was observed that there was no statistically significant difference, at a level of 1%, between the groups: G1 and G3, G1 and G4, and between G3 and G4, and there was statistically significant difference at a level of 1%, between group G2 and the other groups, with G3 having the greatest roughness (ANOVA P < 0.01).

Cyclic fatigue testing and metallographic analysis of nickel-titanium rotary instruments

INTRODUCTION

The aim of this study was to compare cyclic fatigue resistance of four nickel-titanium rotary systems and to evaluate their surface, fractographic, and matrix morphology.

METHODS

Four models of endodontic rotary files (EasyShape [Komet/Gebr. Brasseler, Lemgo, Germany], ProTaper [Dentsply Maillefer, Ballaigues, Switzerland], NRT [MANI Inc, Toshigi-Ken, Japan], and AlphaKite [Komet/Gebr. Brasseler]) were subjected to fatigue testing in artificial canals with angle of curvature of 45° and 60° and a radius of curvature of 5 mm until fracture occurred. Nickel-titanium (NiTi) alloy properties were investigated by light microscopy, environmental scanning electron microscopy (ESEM), and energy dispersive x-ray spectrophotometry (EDS). ESEM analysis was conducted on new files to examine surface characteristics and on fractured samples to identify the crack origin and the fractographic features.

RESULTS

Analysis of variance testing revealed significant differences (P < .001) among the groups. NRT files had the highest fatigue resistance followed by AlphaKite, EasyShape, and ProTaper. All the new files presented surface imperfections. Fractographic analysis found the crack initiation to originate at the level of surface irregularities. Optical microscope inspection of the NiTi alloy matrix disclosed different-sized nonmetallic inclusions among models. EDS analysis of these inclusions showed that they were composed of carbon and oxygen in addition to nickel and titanium. Under light microscopy, austenitic grains appeared larger near the handle and smaller near the tip in all instruments.

CONCLUSIONS

NRT files presented the longest fatigue life. All samples showed surface irregularities and nonmetallic inclusions. Austenitic grains were smaller near the tip than near the handle. The angle of curvature was confirmed to influence the fatigue life of NiTi instruments.

A systematic method for predetermined scanning electron microscope analysis in dental science

Scanning electron microscope evaluation could be criticized if the method adopted to correct for bias is not specified in the study design. Observers can draw conclusions from images unconsciously chosen to best support their research hypotheses, impairing the basic research principle of operator's impartiality. In this study, a systematic observation method has been described and verified for repeatability. The number and the observation points on a certain specimen have been predetermined using a scheme along with observation rules previously established in the research protocol. When our instrument is used at an operating magnification between 500x and 1,000x (corresponding to a frame of 250x190 micro and 120x90 micro, respectively), the method allowed 100% repeatable observation frames, with linear frame errors in finding an observation point of 12.5% in length and 16.8% in height. With modifications to accommodate research objective and statistical requirements, the method could be applied to many SEM observation study.

Defects in nickel-titanium instruments after clinical use. Part 3: a 4-year retrospective study from an undergraduate clinic

The purpose of this study was to analyze the incidence and mode of ProFile (Dentsply Tulsa Dental, Johnson City, TN) instrument separation during a predefined schedule of clinical use by the undergraduate students in a dental school over 4 years. A total of 3,706 ProFile instruments discarded from the same undergraduate students program between 2003 and 2007 were analyzed. The lateral and fracture surfaces of 12 separated instruments were examined by scanning electron microscopy, and the location of the fractures was recorded. The overall proportion of instrument defects was 1.3%; deformation without fracture occurred in 1% and separation in 0.3%. The majority of instrument defects occurred in size 20 (34/48). The ProFile instruments (10/12) failed mostly because of shear stress, whereas only two failed because of fatigue fracture. The results of this study indicated that NiTi rotary instrument system was successfully introduced into an undergraduate endodontic program. Small size files should be considered as single-use, disposable instruments because of the higher possibility of torsional deformation.