Wear and metallographic analysis of WaveOne and reciproc NiTi instruments before and after three uses in root canals

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

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

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

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

In Vitro Evaluation of the Dynamic Cyclic Fatigue Resistance of a New TruNatomy Glider File after Different Cycles of Use

INTRODUCTION

Determination of the glide path is recommended before using rotary instruments. This study aimed to evaluate the dynamic cyclic fatigue resistance of new and used glider rotary instruments in up to 6 root canals.

METHODS

Seventy-two TruNatomy Glider files were used for the preparation of root canals of extracted lower molars, which were then submitted to the dynamic cyclic fatigue test carried out in a curved metallic artificial canal. The instruments were divided into 4 groups (n = 18): Control group, new instruments without any use in the root canal; Group 2U, instruments used in 2 mesial canals; Group 4U, instruments used in 4 mesial canals; Group 6U, instruments used in 6 mesial canals. The time to failure (TF) of the instrument was recorded, and the number of cycles to failure (NCF) was calculated. The data were submitted to 1-way analysis of variance and to the Games-Howell test for multiple comparisons, adopting a significance level of 5%.

RESULTS

TF and NCF were significantly affected by the number of file uses. The Games-Howell test revealed that TF and NCF were significantly greater in the control group than in Group 4U. In Group 2U, TF and NCF were intermediate and not significantly different from the control group. Group 6U had significantly lower TF and NCF than all other groups.

CONCLUSION

The TruNatomy Glider can be used as a glide path for up to 2 mesial canals of mandibular molars, whereas its use on 4 or 6 root canals is not suggested.

Assessing the cyclic fatigue resistance and sterilization effects on replica-like endodontic instruments compared to Reciproc Blue

This study aimed to evaluate the effect of the number of uses and autoclave sterilization on the cyclic fatigue resistance of four replica-like instruments RC Blue; Only One File Blue; Recip One Blue; and Micro Blue compared to the original system Reciproc Blue (VDW, Munich, Germany). The instruments were analyzed by scanning electron microscope (SEM) before being used in root canal instrumentation (baseline). Fifty molars were instrumented by ten instruments (n=10). After sterilization in an autoclave, the  instruments were analyzed by SEM. This procedure was repeated twice more using different molars, totaling 3 rounds of instrumentation, sterilization and SEM analysis. Then, ten different instruments from each brand were tested for cyclic fatigue resistance. Number of uses data were analyzed using Chi-squared analysis, and cyclic fatigue data were analyzed by one-way Anova followed by Tukey's test as the data had normal distribution. The fracture times for all systems had no significant difference, but Micro Blue had significantly lower values than the other systems (p < 0.05). The SEM analysis showed distortions in the instruments after the 3rd use. Therefore, all tested instruments except of Micro Blue have similar resistance to cyclic fatigue, and all are reliable for use in up to 2-cases.

Assessing the cyclic fatigue resistance and sterilization effects on replica-like endodontic instruments compared to Reciproc Blue

This study aimed to evaluate the effect of the number of uses and autoclave sterilization on the cyclic fatigue resistance of four replica-like instruments RC Blue; Only One File Blue; Recip One Blue; and Micro Blue compared to the original system Reciproc Blue (VDW, Munich, Germany). The instruments were analyzed by scanning electron microscope (SEM) before being used in root canal instrumentation (baseline). Fifty molars were instrumented by ten instruments (n=10). After sterilization in an autoclave, the  instruments were analyzed by SEM. This procedure was repeated twice more using different molars, totaling 3 rounds of instrumentation, sterilization and SEM analysis. Then, ten different instruments from each brand were tested for cyclic fatigue resistance. Number of uses data were analyzed using Chi-squared analysis, and cyclic fatigue data were analyzed by one-way Anova followed by Tukey’s test as the data had normal distribution. The fracture times for all systems had no significant difference, but Micro Blue had significantly lower values than the other systems (p < 0.05). The SEM analysis showed distortions in the instruments after the 3rd use. Therefore, all tested instruments except of Micro Blue have similar resistance to cyclic fatigue, and all are reliable for use in up to 2-cases.

The Use of Premixed Calcium Silicate Bioceramic Sealer with Warm Carrier-Based Technique: A 2-Year Study for Patients Treated in a Master Program

Background: Recently several calcium silicate flowable sealers have been introduced as endodontic materials for the root canal. This clinical study tested the use of a new premixed calcium silicate bioceramic sealer in association with the Thermafil warm carrier-based technique (TF). Epoxy-resin-based sealer with the warm carrier-based technique was the control group. Methodology: Healthy consecutive patients (n = 85) requiring 94 root canal treatments were enrolled in this study and assigned to one filling group (Ceraseal-TF n = 47, AH Plus-TF n = 47) in accordance with operator training and best clinical practice. Periapical X-rays were taken preoperatively, after root canal filling and after 6, 12 and 24 months. Two evaluators blindly assessed the periapical index (PAI) and sealer extrusion in the groups (k = 0.90). Healing rate and survival rate were also evaluated. Chi-square tests was used to analyze significant differences between the groups. Multilevel analysis was performed to evaluate the factors associated with healing status. Results: A total of 89 root canal treatments in 82 patients were analyzed at the end-line (24 months). The total drop-out was 3.6% (3 patients; 5 teeth). A total of 91.1% of healed teeth (PAI 1-2) was observed in Ceraseal-TF, with 88.6% in AH Plus-TF. No significant difference was observed on healing outcome and survival among the two filling groups (p > 0.05). Apical extrusion of the sealers occurred in 17 cases (19.0%). Of these, 6 occurred in Ceraseal-TF (13.3%) and 11 in AH Plus-TF (25.0%). Three Ceraseal extrusions were radiographically undetectable after 24 months. All the AH Plus extrusions did not change during the evaluation time. Conclusions: The combined use of the carrier-based technique and premixed CaSi-based bioceramic sealer showed clinical results comparable with carrier-based technique and epoxy-resin-based sealer. The radiographical disappearance of apically extruded Ceraseal is a possible event in the first 24 months.

Impacts of NaOCl and Irritrol irrigation solutions with/without autoclave sterilisation on the cyclic fatigue resistance of different nickel-titanium files

This research aimed to examine the impact of NaOCl and Irritrol solutions with/without autoclave sterilisation on the cyclic fatigue resistance of ProTaper, WaveOne Gold and Reciproc NiTi files. Seventy files in every group were separated into seven subgroups (n = 10) according to irrigation solutions and sterilisation procedures. The mean and standard deviations of the time to fracture was calculated for each group, and the data statistical analysis was performed (P ≤ 0.05). Significantly higher cyclic fatigue resistance was found in Reciproc files than the other types of files. The differences between the control and other subgroups were found to be statistically insignificant (P > 0.05), except for subgroups 5 and 7 (P ≤ 0.05). Immersing NiTi files in NaOCl or Irritrol with sterilisation for three times considerably reduced the cyclic fatigue resistance of these files. Reciproc files exhibited the highest cyclic fatigue resistance in comparison with ProTaper and WaveOne Gold files.

Wear Analysis of Four Different Single-File Reciprocating Instruments before and after Four Uses in Simulated Root Canals

The aim of this study is to assess the surface alterations of four reciprocating instruments before and after the shaping of four resin-simulated root canals. The following four different reciprocating instruments are selected: 10 Reciproc Blue (RB25), 10 WaveOne Gold (WOG), 10 EdgeOne Fire (EOF) and 10 recently introduced instruments OneRECI (OR), for a total of 40 new instruments. Before root canal shaping, each instrument is mounted on a stub in a standardized position and observed using a scanning electron microscope (SEM) to detect any surface alteration, such as microfractures, metal defects, deformations, blunt and disruption of cutting edges, debris, pitting and tip flattening. Micrographs are acquired at the level of the tip, 4 mm, 8 mm and 12 mm from it. After that, each instrument is used in four simulated resin root canals. SEM observation was repeated after the simulated clinical use to assess the wear resistance of the instruments. Surface alterations are registered before and after instrumentation and statistical analysis is performed using a Chi-Square test to verify homogeneity of defects distribution and GLM to evaluate the differences of RMS at baseline and after use for both groups (α level 0.05). Before simulated clinical uses, no alterations are found except for three cases of EOF with metal strips in correspondence to the tip, disruption of the cutting edge of WOG and oily spotting on two different OR. After simulated clinical use, EOF shows a statistically significant difference in terms of spiral distortion and flattening of the cutting edges. The OR shows the highest presence of debris despite the ultrasonic cleaning procedures. No instrument fractures are observed. EOF should be discarded after four clinical uses and carefully inspected after each insertion into root canals. Moreover, tough attention should be paid during disinfection and cleaning procedures after instrumentation considering the copious debris detected in each instrument, particularly in OR.

Noncontact 3D evaluation of surface topography of reciprocating instruments after retreatment procedures

This study evaluated the Reciproc R25 and Pro-R 25 instruments in unused condition, after one and a second use in endodontic retreatment employing a noncontact 3D light interferometer profiler, scanning electron microscopy (SEM) and cyclic fatigue tests. Twenty single-root teeth were instrumented with Reciproc R25 and filled with gutta-percha and sealer. A 3D profiler with a 20x objective using the Mx™ software was used to evaluate the cutting blade surfaces of Reciproc R25 and Pro-R 25 (n=5 per group) in unused condition, after the first and second uses in retreatment procedures. After retreatment, SEM was used to evaluate the topographic features of the used instruments. Cyclic fatigue tests were performed to compare new to used instruments. One-way ANOVA followed by Tukey test was used to compare the tested instruments before and after the first and second uses. Student t-test was used to compare the different instruments and for cyclic fatigue evaluation. No significant differences were observed in the cutting blade surfaces of Reciproc and Pro-R before and after one and two uses (p>0.05). Reciproc without use showed higher Sa and Sq when compared to Pro-R without use (p<0.05). No differences were observed between Reciproc and Pro-R after one and two uses (p>0.05). New and unused Reciproc showed longer time to fracture than Pro-R instruments (p<0.05), and only Pro-R showed differences between new and used instruments (p<0.05). Retreatment procedures with Reciproc and Pro-R did not change the surface topography of instruments. Reciproc had greater resistance to cyclic fatigue compared with Pro-R.

Present status and future directions - Removal of fractured instruments

Success rate of fractured instrument retrieval varies because it is dependent mainly on several factors including the visibility of the fractured instrument, the length of the fractured instrument in relation to the curvature of the canal, and the techniques applied to each case. This review aims to update the present status on removal of fractured instruments to identify factors and variables that could affect the success of fractured instrument retrieval based on both the preparation techniques and the instrument retrieval techniques. On the other hand, future directions of fractured instrument retrieval should focus on management of non-visible fractured instruments since the removal of those instruments are deemed unpredictable with the current techniques, whereas the removal of visible fractured instruments are considered predictable now. Another possible direction of it is there might be no more instrument fracture due to possible significant changes in the root canal preparation technique which may dispense with the use of rotary instruments.

Surface profile of different heat-treated nickel-titanium files before and after root canal preparation

The aim of this study was to evaluate surface wear, presence of microcracks and surface irregularities of WaveOne (WO) and WaveOne Gold (WOG) instruments before and after multiple uses. Eight Primary instruments of the WO and WOG systems were evaluated, each one was used to prepare six mesial canals of extracted human mandibular molars. The surface of the instruments was evaluated before use (T0), after instrumentation of three (T1) and six (T2) root canals. Surface wear was analyzed using a three-dimensional optical profiler and the presence of microcracks and surface irregularities were evaluated using a tabletop scanning electron microscopy. The Friedman test was used to assess surface wear and Kruskal-Wallis test to evaluate the presence of microcracks and surface irregularities, with a 5% significance level. There was a significant increase in wear in both groups at T2, compared to T0 (p=0.0003). The surface wear after instrumentation of six canals (T2-T0) was statistically greater in the WOG group, than in the WO group (p=0.02), where the presence of microcracks was significantly greater and increased after multiple uses (p<0.05). The presence of surface irregularities in the cutting blade before and after use was statistically greater in the WOG group than WO group (p<0.05). Wear of the cutting blade, microcracks and surface irregularities were observed on the surface topography of all the instruments after multiple uses. These surface changes may affect the cutting efficiency of WOG files and increase the risk of fracture of WO files.

Metallurgical Tests in Endodontics: A Narrative Review

Since there are no reviews of the literature on this theme, the aim of this narrative review is to summarize the metallurgical tests used in endodontics, pointing out their functional use and their pros and cons and giving readers a user-friendly guide to serve as an orientation aid in the plethora of metallurgical tests. With this purpose, a literature search for articles published between January 2001 and December 2021 was conducted, using the electronic database PubMed to collect all published articles regarding the metallurgical tests used in endodontics for the evaluation of NiTi rotary instruments. The search was conducted using the following keywords: “metallurgy”, “differential scanning calorimetry” (DSC), “X-ray diffraction” (XRD), “atomic force microscopy” (AFM), “energy-dispersive X-ray spectroscopy” (EDS), “focused ion beam analysis” (FIB) and “Auger electron spectroscopy” (AES) combined with the term “endodontics” or “NiTi rotary instruments”. Considering the inclusion and exclusion criteria, of the 248 articles found, only 81 were included in the narrative review. According to the results, more than 50% of the selected articles were published in one of the two most relevant journals in endodontics: International Endodontic Journal (22.2%) and Journal of Endodontics (29.6%). The most popular metallurgical test was DSC, with 43 related articles, followed by EDS (33 articles), AFM (22 articles) and XRD (21 articles). Few studies were conducted using other tests such as FIB (2 articles), micro-Raman spectroscopy (4 articles), metallographic analysis (7 articles) and Auger electron spectroscopy (2 articles).

Metallurgical characterisation and torsional resistance of blue thermomechanically treated nickel titanium instruments after simulated ex vivo retreatment procedure

To compare used and unused Reciproc Blue and Reciproc after retreatment, the instruments were used in the mesiobuccal canals of maxillary molars with curvature. The torsional resistances were tested and then unused instruments were subjected to XRD, DSC and microhardness tests. Student's t, ANOVA and Tukey's tests were performed (α-level 0.05). The torsional strength of used Reciproc Blue was not significantly different than unused ones (P > .05), while torsional strength of Reciproc decreased significantly (P < .05). DSC and XRD indicated that Reciproc Blue exhibited prominent transformation peaks corresponding austenite to R-phase. Microhardness of Reciproc was significantly higher (P < .05). A second reuse of Reciproc Blue for retreatment could be considered safe in terms of torsional strength. Blue treatment also decreased surface microhardness of the instrument and changed phase composition by increasing the R-phase.

Cyclic fatigue and torsional resistance evaluation of Reciproc R25 instruments after simulated clinical use

BACKGROUND

To assess the influence of multiple uses on the cyclic flexural fatigue and torsional resistance of Reciproc R25 (REC) instruments.

METHODS

256 canals (2 for each mandibular molar) were prepared using Reciproc R25 instruments. A total of 96 25-mm-long Reciproc R25 instruments were divided in six groups (n=8) on the basis of different number of canal shaped: new instruments (control group), 1, 2, 3, 4 or 6 canals shaped during simulated clinical use for other groups respectively. Sixteen files were used for each of the six groups (8 instruments for cyclic fatigue test and 8 ones for torsional test). Times to fracture (TtF) for cyclic fatigue and ultimate torsional strength and angle of rotation to fracture for torsional resistance were recorded. Data were statistically evaluated by the analysis of variance (ANOVA) with P<.05.

RESULTS

As for cyclic fatigue resistance, there was no significant difference between new REC and REC used in one, two and three canals respectively (P>.05). REC used in four and six canals showed significant lower times to fracture when compared with other groups (P<.05) with REC used in six canals showing the significant lowest times to fracture (P<.05). Considering torsional resistance parameters, no significant difference was observed between the new and used instruments (P>.05).

CONCLUSIONS

REC25 files showed a significant decrease in cyclic fatigue resistance only when used in four or more molar canals while their torsional behavior was not affected by multiple uses.

Effect of number of uses and sterilization on the instrumented area and resistance of reciprocating instruments

Objectives

This study evaluated the effect of repeated uses and autoclaving in the instrumented area, fracture resistance, and time of instrumentation of thermally treated nickel-titanium reciprocating systems.

Materials and Methods

Two hundred simulated canals were instrumented using Reciproc Blue and WaveOne Gold. Each file was used up to 10 times or until fracture. The instrumented area was measured in pre- and post-operative images, using ImageJ software. Kaplan-Meier survival analysis evaluated the number of uses of instruments before fracture. Instrumented area and time of instrumentation were analyzed by Mann-Whitney U test and Kruskal-Wallis. Correlations among the number of uses and instrumented area were measured. The level of statistical significance was set at p < 0.05.

Results

Reciproc Blue presented a higher estimated number of uses in comparison with WaveOne Gold (p = 0.026), but autoclaving did not affect the resistance to fracture of instruments (p > 0.05). The instrumented area was different among the evaluated groups (p = 0.039), and the instrumented area along the uses of both tested instruments was reduced. With the time of instrumentation, there was also a significant difference among the evaluated groups; the groups without sterilization cycles were faster, in comparison to those submitted to autoclaving (p = 0.010).

Conclusions

Reciproc Blue was more resistant than WaveOne Gold, suffering later fracture. Additionally, the sterilization cycles did not influence the estimated number of uses of thermally treated reciprocating instruments, but the instrumented area of root canals was reduced along with the repeated uses of both instruments.

Impact of Endodontic Instrumentation on Surface Roughness of Various Nickel-Titanium Rotary Files

OBJECTIVES

 The aim of the present study was to evaluate the surface roughness (SR) of various nickel-titanium (NiTi) rotary endodontic instruments (ProTaper Next [PTN], WaveOne Gold [WOG], and ProTaper Gold [PTG]) before and after root canal instrumentation.

MATERIALS AND METHODS

 For each type (PTN, WOG, and PTG), the endodontic instrumentation was performed using extracted mandibular molar teeth's curved mesial root canals (curvature: 20-40 degrees) after determining the working length. Each NiTi file was cleaned, and sterilized following preparation of four root canals and characterized for surface properties before and after endodontic instrumentation using a contact-mode three-dimensional surface profiler. The data were analyzed statistically using Statistical Package for the Social Sciences for SR parameters including average surface roughness value (Sa), root mean square roughness (Sq), and peak to valley height (Sz).

RESULTS

 Preinstrumentation assessment revealed a significant difference for all the three SR variables (p < 0.05) for the cutting blade and the flute area. WOG instruments showed the highest SR values (p = 0.000). The postinstrumentation assessment revealed significant differences in SR values in the blade and the flute between the three groups (p < 0.05), with WOG and PTG exhibiting the highest values in the blade and flute sections, respectively.

CONCLUSIONS

 The SR parameters of intact PTN, WOG, and PTG NiTi files vary and that was increased following the endodontic instrumentation.

In-Depth Metallurgical and Microstructural Analysis of Oneshape and Heat Treated Onecurve Instruments

OBJECTIVE

To define surface, mechanical, microstructural and metallurgical features of conventional One-Shape (OShape) and heat-treated OneCurve (OCurve) nickel-titanium instruments.

METHODS

Instruments were analysed by scanning electron microscopy (SEM) on new instruments and after simulated clinical use (SCU). Cyclic fatigue testing was performed and the number of cycles to fracture (NCF) and the length of the fractured instruments were measured (Mann-Whitney test). Fractured instruments during cyclic fatigue testing were then inspected by SEM fractographic analysis. Field emission gun scanning scanning electron microscopy (FEG-SEM), energy-dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy were used to assess alloy surface chemistry. Focused ion beam (FIB) was performed to analyse the oxide layer on the surface of OCurve before and after SCU. X-Ray diffraction (XRD), metallographic evaluation and differential scanning calorimetry (DSC) were used to determine martensitic/austenitic phase transformation temperatures.

RESULTS

SEM observations on new instruments revealed a smooth regular surface with flattened milling grooves. No wear features were detected after SCU. OCurve exhibited a higher cyclic fatigue resistance (P<0.05), slower crack propagation and a surface layer of TiO2. Metallographic analysis and XRD showed the prevalence of martensitic grains on OCurve instruments that were stable at body temperature as confirmed by DSC analysis. Furthermore, DSC demonstrated a shift in the temperature transformation ranges suggesting an increase of martensite phase in autoclaved OCurve instruments.

CONCLUSION

Heat treatment processes were confirmed as a valid enhancement of the properties of the new generation NiTi instruments. OCurve presented a significant improvement over OShape regarding both mechanical and metallurgical characteristics.

Effects of clinical use of NiTi reciprocating instruments on cyclic and torsional resistance, and on roughness

The aim of the present study was to evaluate the cyclic fatigue, torsional resistance and surface roughness of Reciproc R25 instruments in four different situations, namely as new instruments and as instruments tested after clinical preparation of one, two or three maxillary molars with four root canals. The total time required to perform each root canal preparation was recorded. Cyclic fatigue resistance was determined by the time to fracture using a customized testing device (n = 10 per group). The torsional test evaluated the torque and angle of rotation to failure according to ISO 3630-1 (n = 10 per group). The roughness of the working parts of new and used instruments was evaluated with a profilometer (n = 5 per group). Statistical analysis was performed using one-way ANOVA and Tukey's test. The level of significance was set at 5%. No fractures or deformations were observed after clinical use. Higher preparation time was needed during the third use of the instruments for all root canals (p < 0.05). There were no significant differences among the groups in regard to either cyclic fatigue or torsional resistance (p > 0.05). Regarding the roughness measurements, groove depth was higher on new and one- versus two- or three-maxillary-molar-prepared instruments (p < 0.05). It can be concluded that the clinical use of Reciproc instruments increased preparation time and decreased surface roughness. However, clinical use did not affect the cyclic fatigue or torsional resistance of the Reciproc instruments.

Scanning electron microscopy analysis of conventional and controlled-memory nickel titanium files before and after multi-uses in root canals

The current study aimed to examine changes in the physical properties of conventional and CM nickel-titanium instruments after repeated clinical use, disinfection-sterilization processes, using scanning electron microscopy (SEM). Sixty extracted mandibular molar mesial roots were used in this ex vivo study. The 60 teeth underwent final apical shaping (#25/.06) by the Revo-S SU (Revo-S Group: #25/.06; Micromega; n = 10) and Hyflex CM (Hyflex CM group: #25/.06; Coltene-Whaledent; n = 10) groups. One instrument of each group was used to shape six different teeth (Revo-S SU in 3 MB and 3 ML canals, and Hyflex CM in 3 MB and 3 ML canals), sequentially. The physical changes evident on the surfaces of the files after sequential use and sterilization processes were analyzed by SEM after the first, third, and sixth use. The first SEM examination was performed immediately after removal from the packages. Following first SEM examination, the files were sterilized before the first use as would be customary in practice. Qualitative evaluations were made by two evaluators, according to the following criteria: tip deformation, cutting edge deformation, debris, and microfracture. Revo-S showed a significant difference in cutting edge deformation, tip deformation, and microcrack formation, as compared to Hyflex CM. There was no significant difference between the groups in debris with the increasing number of uses. In this study, Hyflex CM (CM nickel-titanium) files showed better performance in terms of deformation and microcrack formation as the number of uses increased than did Revo-S (conventional nickel-titanium) files.

Does the type of endodontic access influence in the cyclic fatigue resistance of reciprocating instruments?

INTRODUCTION

The aim of the present study was to compare the cyclic fatigue resistance of Reciproc R25 (R25) and Reciproc Blue R25 (R25B) instruments, after simulated clinical use in traditional (TradAC) and ultraconservative (UltraAC) endodontic access cavities.

METHODS

Forty mandibular molars were randomly assigned into the following groups, according to the type of access and instrument to be used: TradAC and R25, TradAC and R25B, UltraAC and R25, and UltraAC and R25B. Teeth were accessed accordingly, and the root canals were prepared using "RECIPROC ALL" kinematics. The cyclic fatigue resistance of the forty used instruments was obtained measuring the time to fracture in an artificial stainless-steel canal. Ten brand new R25 and R25B were used as control groups. The fracture surfaces and the side cutting edges of the instruments were examined with a scanning electron microscope. Data were statistically analyzed using one-way ANOVA and post hoc Tukey tests with a significance level of P < 0.05.

RESULTS

R25B instruments showed significantly higher cyclic fatigue resistance than R25, regardless of the access cavity type (P < 0.05). No differences were observed in the cyclic fatigue resistance between instruments without simulated clinical use and used in TradAC (P > 0.05). R25 and R25B used in UltraAC showed significantly lower cyclic fatigue resistance compared with the instruments used in TradAC and without simulated clinical use (P < 0.05).

CONCLUSIONS

R25B files showed improved cyclic fatigue resistance than R25. The use of R25B and R25 files in mandibular molars with UltraACs decreased their cyclic fatigue resistance, compared with TradAC.

CLINICAL RELEVANCE

The use of Reciproc and Reciproc Blue files in mandibular molars with ultra-conservative endodontic access cavities reduced their cyclic fatigue resistance. Clinicians should be aware about the reduced cyclic fatigue resistance of these files when used in mandibular molars with UltraAC, due to the synergistic effect of access angulation and severe curvature induced in the endodontic files.

Influence of different motions on the cyclic fatigue resistance of Reciproc and Reciproc Blue endodontic instruments

Aim

The aim of this study was to evaluate the cyclic fatigue resistance of Reciproc (RCP) and RPC Blue (RCPB) instruments used in continuous rotation, "RECIPROC" mode, and "WAVEONE" mode.

Materials and Methods

Sixty RCP and 60 RCPB R25 files were used. For each file type, three groups (n = 20) were defined depending on the used kinematics: continuous rotation, "RECIPROC" mode, and "WAVEONE" mode. A stainless-steel artificial canal with 60° angle and 5-mm radius of curvature was milled reproducing the size and taper of the used files. The test device was electrically heated to 35°C to simulate the clinical environment. All files were reciprocated or rotated until fracture. The time to failure and the length of the fractured fragments were measured. A fractographic examination was performed by scanning the electron microscopy to confirm the cause of fracture. Collected data underwent a two-way analysis of variance (α = 0.05).

Results

RCPB files exhibited better cyclic fatigue resistance than RCP. The "RECIPROC" motion yielded greater cyclic fatigue resistance than the "WAVEONE" movement; the least resistance was observed in the continuous rotation groups. No significant differences were found among groups in terms of length of the fractured fragment. The fractographic analysis confirmed that all scanned samples separated due to cyclic fatigue.

Conclusions

Within the limitation of the present study, the "RECIPROC" mode increased the cyclic fatigue resistance of the tested instruments compared to "WAVEONE" mode and continuous rotation. To prevent RCP and RCPB file separation, motion kinematics other than the native "RECIPROC" movement should be discouraged in the clinical setting.

The potential effect of instrumentation with different nickel titanium rotary systems on dentinal crack formation-An in vitro study

The potential mechanical impact of different rotary systems used for root canal preparation has been a matter of debate for long. The aim of this study was to explore the incidence of dentinal cracks after root canal instrumentation with various rotary systems, in vitro. One hundred and eighty intact lower central incisors were selected and randomly divided into fourteen treatment groups (n = 12/group) and a control group (n = 12). After decoronation, the root canals were instrumented with fourteen different rotary systems (E3, E3 azure, NT2, Hyflex CM, Hyflex EDM, 2Shape, OneCurve, ProTaper Next, ProTaper Gold, WaveOne Gold, Mtwo, Reciproc Blue, TF adaptive, K3XF). All roots were horizontally sectioned at 3, 6, and 9 mm from the apex with a low-speed saw under water-cooling. The slices were then examined under stereomicroscope for dentinal cracks. No cracks were found in the control group. Cracks were found in all treatment groups, predominantly in the 3 mm slices. There was no statistically significant difference in the number of cracks when comparing the different systems to each other at any section level. At 3 mm, however, five of the studied systems, namely K3XF (p = 0.004), Protaper Next (p = 0.001), Reciproc Blue (p<0.001), TF adaptive (p = 0.050), and 2Shape (p = 0.009) presented a significantly higher number of cracks than the control group. Within the limitations of this study, instrumented canals presented dentinal cracks, while uninstrumented ones presented no cracks after sectioning. There seems to be no significant difference among the tested systems regarding crack formation in the instrumented root canal wall. Crack formation occurred irrespective of the motion of the rotary system (rotational or reciprocation). Further studies are needed to clarify the factors that contribute to crack formation in the case of each individual rotary system.

Topographic changes in NiTi rotary instruments after the clinical use

Surface alterations of instruments were investigated after single and multiple uses in the root canals. XP-endo Shaper (n = 5) and WaveOne GOLD (n = 5) files were used until the separation of the instruments occurred. The apical 3-mm and separated fragments were analysed by SEM to determine the changes in the instruments and the cross-sections of the separated fragments. Each group was divided into five subgroups: control, first, second, third and fourth molar. The results were reported descriptively for each group. In the XP-endo Shaper group, microcracks started to appear after the second use, and pitting and galvanic corrosion occurred after the third use. During the fourth use, microcracks propagated, resulting in ductile fracture while it happened after the third use in the second group. The single use of XP-endo Shaper and WaveOne GOLD was safe without any major changes on their surfaces. Reciprocating motion was not necessarily superior to full rotation motion.

Fracture incidence of WaveOne Gold files: a prospective clinical study

AIM

This prospective clinical study evaluated the incidence of instrument fracture observed after single-file root canal treatment of molars using WaveOne Gold instruments.

METHODOLOGY

Three standardized, experienced and calibrated specialists treated 750 maxillary and mandibular molars with curvatures less than 45° (2691 root canals) over a 12-month period. All the treatments were performed in a single session. A total of 1104 WaveOne Gold instruments were used, including 38 small, 750 primary, 228 medium and 88 large instruments. Intracanal procedures were performed according to the manufacturer's recommendations, and each instrument was used in a single clinical case. The instruments were examined after their removal from the canal, under an operating microscope at 8× magnification.

RESULTS

No fractures were observed in any of the 1104 instruments used.

CONCLUSIONS

No fractures of WaveOne Gold reciprocating instruments occurred during root canal preparations performed in maxillary and mandibular molars with curvatures less than 45° when used strictly according to the manufacturer's recommendations and applied in a single clinical case.

Cyclic Fatigue Resistance of Multiused Reciproc Blue Instruments during Retreatment Procedure

INTRODUCTION

Root canal retreatment procedure may reduce the mechanical resistance of nickel-titanium instruments and increase the frequency of instrument fracture. The aim of the present study was to evaluate the effect of multiuse of Reciproc Blue R25 instruments on cyclic fatigue resistance during retreatment procedure in mandibular molar teeth.

METHODS

Forty-eight Reciproc Blue R25 files were included in the study. In control group, 12 new Reciproc Blue R25 instruments were subjected to cyclic fatigue test by using a stainless steel artificial canal with a 90° angle and 3-mm radius of curvatures. In experimental groups, Reciproc Blue R25 files (n = 12) were used to remove the root canal filling (RCF) material of 1, 2, and 3 molar teeth, respectively. Then cyclic fatigue tests of these 36 instruments were performed. The number of cycles to fracture (NCF) and the length of the fractured fragment were calculated for each instrument. Working time for retreatment procedures was determined in seconds with a digital chronometer. The data were analyzed by using one-way analysis of variance followed by post hoc Tukey test and mixed-effect analysis (P = .05).

RESULTS

No significant difference was found between NCF values of new and first time used files (P > .05), but NCF values of new and first time used files were significantly higher than those of second and third time used files (P < .05). The second and third time used files revealed no difference (P > .05). As the number of uses increased, the average time for retreatment procedure statistically extended (P < .05).

CONCLUSIONS

Reciproc Blue R25 instrument can be used to remove RCF material of 2 molar teeth. However, because of its decreased NCF values, multiple use over 2 molars may not be suggested.

Evaluation of the usage-induced degradation of Genius and Reciproc nickel-titanium reciprocating instruments

The aim of this study was to characterize the main features and the usage-induced degradation of the Genius file after four severely curved root canal instrumentations and to compare their properties to the Reciproc files. Brand new and ex vivo used files were analysed by scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), differential scanning calorimetry (DSC), X-ray diffraction (XRD), optical metallography, and nano-indentation to disclose their morphological, chemical, mechanical, thermal, and phase composition features. Nano-indentation data were statistically analysed using the Student's t test for normal distribution or the Kolmogorov-Smirnov test for not-normal distributions. SEM analysis showed the presence of micro-cracks near the tip on both files after ex vivo usage test. EDS analysis confirmed that both files are manufactured from an almost equiatomic NiTi alloy. DSC analysis revealed that the transition temperature of the Genius is below 20 °C, while that of the Reciproc is above 20 °C. XRD analysis of Genius files identified cubic B2 austenite with minor peaks of residual monoclinic B19 martensite, while the contemporaneous presence of martensite, austenite and hexagonal R-phase was observed in the Reciproc files. Significant differences in nanohardness and modulus of elasticity (P < .05) were observed in both Genius and Reciproc files before and after use. The collected results showed that both instruments can be safely used as single-use files.

Shaping effectiveness and surface topography of reciprocating files after multiple simulated uses

This in vitro study assessed morphological changes and efficiency of reciprocating files after multiple uses. Sixty standardized Endo Training Blocks and 10 ReciprocR25 files were selected (six blocks for each file). Each file was its own control (before use vs. after each instrumentation). The instruments were used according to the manufacturer's instructions, and scanning electron microscopy was used to observe fatigue cracks, metal strips/metal flash, pitting, fretting, debris, disruption of the cutting edge, and plastic deformations after each instrumentation. The presence of seven wear variables was scored semiquantitatively by viewing micrographs collected before and after use. The prepared areas in resin blocks were calculated and compared by using AutoCAD software. The control group had significantly lower values for all wear variables except fretting and plastic deformation. The presence of fatigue cracks and metal strips/metal flash significantly differed between unused instruments and instruments used four or five times, in all observed sections. The area of instrumented Endo Training Blocks significantly differed in relation to the number of instrument uses. The Reciproc files wore progressively, and repeated use affected their shaping efficiency in simulated canals.

Topographic and Chemical Analysis of Reciprocating and Rotary Instruments Surface after Continuous Use

This study aimed at evaluating the changes in surface characteristics and NiTi content of reciprocating and rotary instruments after continuous use. Thirty brand-new instruments were assigned to 3 groups (n=10): PNX1 Group - ProTaper Next system - instrument X1; PNX2 Group - ProTaper Next system - instrument X2 and WO Group - WaveOne system - Primary instrument 25.08. The instruments were used to prepare 60 simulated root canals. Analysis of surface characteristics by scanning electron microscopy (SEM) and chemical analysis of Ni and Ti content by energy-dispersive spectroscopy (EDS) were performed before and after the first and third use of the instruments. Only WO Group had significant increase in the quantity of defects and deformations after the third use (p<0.05). PNX1 Group had significant decrease in Ni content after the third use, in comparison with the unused instruments (p<0.05). PNX1 Group had no decrease in Ti content throughout the time of use (p>0.05), however, in PNX2 Group, there was significant decrease in the different time interval of analysis (p<0.05). Continuous use promoted increase in defects and deformations only for WaveOne instruments. Chemical composition presented significant changes according to the time of instruments use.

The effect of root canal preparation on the surface roughness of WaveOne and WaveOne Gold files: atomic force microscopy study

Objectives

To examine the surface topography of intact WaveOne (WO; Dentsply Sirona Endodontics) and WaveOne Gold (WOG; Dentsply Sirona Endodontics) nickel-titanium rotary files and to evaluate the presence of alterations to the surface topography after root canal preparations of severely curved root canals in molar teeth.

Materials and Methods

Forty-eight severely curved canals of extracted molar teeth were divided into 2 groups (n = 24/each group). In group 1, the canals were prepared using WO and in group 2, the canals were prepared using WOG files. After the preparation of 3 root canals, instruments were subjected to atomic force microscopy analysis. Average roughness and root mean square values were chosen to investigate the surface features of endodontic files. The data was analyzed using one-way analysis of variance and post hoc Tamhane's tests at 5% significant level.

Results

The surface roughness values of WO and WOG files significantly changed after use in root canals (p < 0.05). The used WOG files exhibited higher surface roughness change when compared with the used WO files (p < 0.05).

Conclusions

Using WO and WOG Primary files in 3 root canals affected the surface topography of the files. After being used in root canals, the WOG files showed a higher level of surface porosity value than the WO files.

Noncontact three-dimensional evaluation of surface alterations and wear in NiTi endodontic instruments

The aim of this study was to undertake a qualitative and quantitative assessment of nanoscale alterations and wear on the surfaces of nickel-titanium (NiTi) endodontic instruments, before and after use, through a high-resolution, noncontact, three-dimensional optical profiler, and to verify the accuracy of the evaluation method. Cutting blade surfaces of two different brands of NiTi endodontic instruments, Reciproc R25 (n = 5) and WaveOne Primary (n = 5), were examined and compared before and after two uses in simulated root canals made in clear resin blocks. The analyses were performed on three-dimensional images which were obtained from surface areas measuring 211 × 211 µm, located 3 mm from their tips. The quantitative evaluation of the samples was conducted before and after the first and second usage, by the recordings of three amplitude parameters. The data were subjected to statistical analysis at a 5% level of significance. The results revealed statistically significant increases in the surface wear of both instruments groups after the second use. The presence of irregularities was found on the surface topography of all the instruments, before and after use. Regardless of the evaluation stage, most of the defects were observed in the WaveOne instruments. The three-dimensional technique was suitable and effective for the accurate investigation of the same surfaces of the instruments in different periods of time.

Presence of Metallic Microfragments on Dentinal Walls and Instrument Defects following Root Canal Preparation

AIM

To determine the presence of metallic microfragments and their elemental composition in the dentinal walls of root canals following preparation using different endodontic instruments and to assess the active cutting edges of instruments with regard to structural defects.

MATERIALS AND METHODS

A total of 108 molar teeth were selected and prepared using different endodontic instruments. Teeth were randomly divided into nine groups of 12 teeth each, according to the instruments employed: Manual systems -K-FlexoFile, K-File, and Hedstroem; rotary systems - ProTaper Next, Mtwo, BioRaCe; and reciprocating systems - Reciproc, Unicone, and WaveOne. Both root canals and instruments were assessed using scanning electron microscopy, and the elemental composition of metallic microfragments was determined using energy-dispersive X-ray spectroscopy.

RESULTS

Metallic microfragments were found in the groups prepared with both manual and reciprocating instruments, with no statistically significant differences between groups, thirds, or presence of metallic microfragments (p ≥ 0.05). Moreover, all groups presented structural defects in both new and used instruments; however, rotary instruments (ProTaper Next, Mtwo 702, BioRaCe) were the ones with the lowest number of defects, at statistically significant differences in comparison with other instruments (p < 0.05).

CONCLUSION

The presence of metallic microfragments on dentinal walls following root canal preparation was associated with manual and reciprocating instrumentation. Furthermore, rotary instruments were the ones with the lowest number of defects. Considering the outcomes measured in this study, rotary instruments performed better than the other two groups, as they were associated with the lowest number of metallic microfragments and structural defects.

CLINICAL SIGNIFICANCE

During root canal preparation, operative procedures may induce changes to the root canal shape, as well as the release of metallic fragments resulting from the action of instruments on dentinal walls. Therefore, it is important to determine, among the different techniques used for this purpose, which ones are least susceptible to this occurrence.

Fracture Incidence of WaveOne and Reciproc Files during Root Canal Preparation of up to 3 Posterior Teeth: A Prospective Clinical Study

INTRODUCTION

Reciprocating instruments were developed to improve and simplify the preparation of the root canal system by allowing greater centralization of the canal and requiring a shorter learning curve. Despite the risk of instrument separation, using a reciprocating instrument in more than 1 case is a relatively common clinical practice. The aim of this study was to evaluate the fracture resistance of Reciproc (R25; VDW, Munich, Germany) and WaveOne (Primary; Dentsply Maillefer, Ballaigues, Switzerland) instruments according to the number of uses during the preparation of root canals in up to 3 posterior teeth.

METHODS

A prospective clinical study was conducted by 3 experienced specialists who performed treatment of 358 posterior teeth (1130 canals) over a period of 12 months using 120 reciprocating instruments, 60 of which were Reciproc R25 and 60 were WaveOne Primary. The motion used during instrumentation followed the recommendations of the respective manufacturers. After each use, the instruments were observed under a dental operating microscope at 8× magnification. In the case of fracture or deformation, the instrument was discarded.

RESULTS

None of the instruments showed any signs of deformation, but 3 instruments fractured (0.26% of the number of canals and 0.84% of the number of teeth). All fractures occurred in mandibular molars (1 WaveOne Primary file during the third use and 2 Reciproc R25 files, 1 during the first use and the other during the third use).

CONCLUSIONS

There was a low incidence of fracture when reciprocating files were used in up to 3 cases of endodontic treatment in posterior teeth.

Single file reciprocating systems: A systematic review and meta-analysis of the literature: Comparison of reciproc and WaveOne

The introduction of single-file nickel-titanium (NiTi) reciprocating systems has been a major breakthrough in the field of endodontics. Thus, the aim of this study was to compare the available reciprocating systems, Reciproc and WaveOne, using a meta-analysis with different parameters. A comprehensive electronic literature search for Reciproc and WaveOne using PubMed and Google scholar was initially conducted in September 2014 and updated in September 2016. Inclusion and exclusion criteria were then established. Twenty-six studies were qualified for the systematic review, and only three studies were considered for the meta-analysis using cyclic fatigue resistance as the main parameter. The time to fracture for the Reciproc and WaveOne systems ranged from 119.7 sec to 156.4 sec and 74.8 sec to 99.6 sec, respectively. The pooled difference in mean time to fracture was longer for the Reciproc system by 45.6 sec. This difference was statistically significantly at P value < 0.001. In conclusion, our study supports the finding that Reciproc is more resistant to cyclic fatigue than WaveOne. However, with regard to other parameters, mixed results were obtained. Well-designed randomized clinical trials comparing both systems under the same experimental conditions should be done in future studies.