Comparison of nickel-titanium file distortion using electric and air-driven handpieces

The use of rotary instrumentation has increased dramatically in endodontics. Air-driven and electric handpieces are both currently available for use with the nickel-titanium files. To date no studies have compared the frequency of instrument separation and/or distortion while using the two types of handpieces with rotary files. The purpose of this study was to determine whether there is a difference in the frequency of file separation/distortion when an electric handpiece is compared with an air-driven handpiece. Extracted human molar teeth were instrumented with nickel-titanium Profile ISO .04 taper rotary files (Dentsply Tulsa Dental Products, Tulsa, OK) under controlled conditions and the results examined for statistical significance. The teeth chosen for the study fit the following criteria: minimal caries, curvature of any root no greater than 60 degrees and at least one root with a minimum of 30-degree curvature. The air-driven handpiece was used at 167.67 rpm and the electric handpiece at 150 rpm per manufacturer's recommendations. Files were examined both before and after use to evaluate whether breakage or deformation had occurred. There was no significant difference in file breakage or distortion when the handpieces were compared. There were, however, a significantly greater number of file separations/ distortions noted in the #8 Profiles (ISO size 20) than with the other files. It may be prudent to view this file as a disposable instrument.     

Cyclic fatigue testing of ProTaper NiTi rotary instruments after clinical use

PURPOSE: The purpose of this study was to evaluate the cyclic fatigue of ProTaper nickel-titanium (NiTi) rotary instruments (Tulsa Dental, Tulsa, Okla) after multiple clinical uses. STUDY DESIGN: Two hundred twenty-five ProTaper instruments were divided into 3 groups: A = 75 used as controls, B = 75 used in 2 molars (6-8 canals), and C = 75 used in 4 molars (12-16 canals). The number of rotations to breakage and the fractured tip length were recorded for each file and the mean was calculated by ANOVA. RESULTS: No S1-2 or F1-2-3 instrument separated during intracanal use, even if they were reused for a number of cases (x 4 molar cases). CONCLUSION: It is clear that prolonged reuse of NiTi rotary instruments strongly affects instruments' fatigue, but our data suggest the hypothesis that other factors (primarily errors and misuse) may be more accountable for intracanal instrument separation. Further studies could assess the cyclic fatigue of each instrument at different levels of the shaft by altering the radius of curvature.     

Assessment of the Separation Incidence of Reciprocating WaveOne Files: A Prospective Clinical Study

Introduction

Despite metallurgical advancements in the nickel-titanium file manufacturing process, file separation remains a concern. The purpose of this prospective clinical study was to assess the separation incidence of the reciprocating WaveOne file (Dentsply Tulsa Dental Specialties, Tulsa, OK) when used to prepare root canals of posterior teeth.

Methods

File separation incidence was assessed over an 18-month period in which 4 experienced and calibrated endodontists performed conventional endodontic treatment on posterior teeth using the WaveOne file system. The separation incidence was determined based on both the number of teeth and the number of canals instrumented during this time period.

Results

A total of 2,215 canals (711 teeth) were treated. Three instruments (two 21.06 and one 25.08) separated during use and were deemed to be irretrievable. The overall instrument separation incidence in relation to the number of canals shaped was found to be 0.13% (0.42% teeth).

Conclusions

Based on the results of this study, the incidence of endodontic instrument separation when using the WaveOne reciprocating file was considerably low.     

A scanning electron microscopy evaluation of microfractures, deformation and separation in EndoSequence and Profile nickel-titanium rotary files using an extracted molar tooth model

The development of microfractures in the EndoSequence nickel-titanium rotary (NTR) file (Brassler USA, Savannah, GA) and Profile NTR file was evaluated by using scanning electron microscopy (SEM). Seventy-three maxillary buccal roots and 53 mandibular mesial roots with an average canal curvature of 37 degrees were randomly assigned to one of three groups and prepared with 21-mm .06 taper NTR files as follows: (1) EndoSequence at 300 rpm, (2) EndoSequence at 600 rpm, and (3) ProFile at 300 rpm. File sizes .45 to .20 were used in a crown-down technique to a master apical file (MAF) size of .35/.06. The MAF instruments were evaluated by SEM before use, after completion of 7 canals, and after completion of 14 canals. All EndoSequence instruments developed microfractures by the seven-canal evaluation. The ProFile instruments showed no microfractures at the 7- or 14-canal evaluations. EndoSequence files separated at a higher rate than ProFile instruments. Under the conditions of this study, unique file design and electropolishing did not inhibit the development of microfractures in EndoSequence NTR.     

Comparison of distortion and separation utilizing profile and Pow-R nickel-titanium rotary files.

The purpose of this study was to determine whether there was a difference in the frequency of file distortion and separation between nickel-titanium (Ni-Ti) ProFile 0.04 ISO taper rotary files and Ni-Ti Pow-R 0.04 ISO taper rotary files. For this study, 60 mesial root canals in 30 human mandibular first molars were chosen with the curvature angle of the mesiobuccal and mesiolingual canals of the same tooth within five degrees. ProFile and Pow-R files were randomly assigned to either the mesiobuccal or mesiolingual canal of the same tooth. Instrumentation proceeded per the manufacturer's recommendations, in a crown-down technique, using Gates Glidden burs and rotary files in sizes #50 to #20. Positive and negative controls were used. The instruments were evaluated for signs of distortion or separation by three independent evaluators using magnification under microscope. A total of 420 files were evaluated, 210 files for Pow-R and 210 files for ProFile. There was no statistically significant difference in the incidence of instrument distortion or separation between the two file systems that were studied.     

Apical displacement produced by rotary nickel-titanium instruments and stainless steel files

The aim of this study was to evaluate the apical displacement produced by different rotary nickel-titanium instruments, testing the hypothesis that rotary systems with nickel-titanium instruments produce lower mean values of apical displacement than stainless steel hand instruments. A total of 100 maxillary permanent first molars were selected for the study. The mesiobuccal roots were sectioned at the top cervical third and embedded in blocks of self-curing resin. The specimens were randomly divided into 5 groups and the root canals were prepared using the following nickel-titanium instruments: Group 1 - Quantec system 2000 (Analytic Endodontics, Mexico); Group 2 - Pro-File T.0.04 (Dentsply/Maillefer, Switzerland); Group 3 - Pro-File Series 29 T.0.04 (Dentsply Tulsa, Switzerland); Group 4 - Pow-R T.0.02 (Moyco-Union Broach, USA). Specimens in Group 5 were prepared using stainless steel hand instruments Flexofile (Dentsply/Maillefer, Switzerland). All root canals were previously submitted to cervical preparation using Orifice Shaper instruments #1, 2, 3 and 4 (Dentsply/Maillefer, Switzerland). After odontometry, the remaining root canal was shaped employing increasingly larger instruments, so that the final instrument corresponded to Quantec #9, Pro-File Series 29 #6, and #35 for the other groups. Specimens in Groups 1 to 4 were prepared using an electric handpiece with 16:1 reduction at 350 rpm. The specimens in Group 5 were manually prepared. Apical displacement was measured and recorded by means of radiographic superimposition on a specific desk. Statistical analysis (ANOVA) of the results revealed that all groups presented apical displacements. Considering only the nickel-titanium instruments, Group 4 showed the lowest mean value while Groups 2 and 3 produced the highest mean apical displacement values (p<0.001).     

Defects in Nickel-Titanium Instruments after Clinical Use. Part 5: Single Use From Endodontic Specialty Practices

IntroductionSingle use of endodontic nickel-titanium (NiTi) instruments has been recommended to reduce instrument fatigue and the possibility of cross-contamination. The purpose of this study was to evaluate the defects of three NiTi rotary systems (ProFile series 29 [Dentsply Tulsa Dental Products, Tulsa, OK], ProFile [Dentsply Tulsa Dental Products], and ProTaper [Dentsply Maillefer, Ballaigues, Switzerland]) that were discarded after single use by two endodontic clinics.MethodsA total of 1,071 ProFile .04, 432 ProFile series 29 .04, and 1,895 ProTaper rotary instruments were collected over 12 months and analyzed. These discarded files were ultrasonically cleaned and autoclaved. The lateral view of the deformed instruments and fracture surface of the separated instruments were examined by scanning electron microscopy. Qualitative X-ray energy-dispersive spectrophotometric (EDS) spot analyses were performed on particles adherent to the surface and those apparently wedged in surface microcracks.ResultsThere were no fractures or deformations in the ProFile Series 29. The overall prevalence of deformation was 2.9% in ProTaper and 0.75% in ProFile. The incidence of instrument separation was 0.26% in ProTaper, whereas no fractures occurred in ProFile instruments. The majority of instrument defects occurred in size 25 (6/8) for ProFile and in Sx for ProTaper (22/60). The separated ProTaper instruments failed mostly because of shear stress. Some surface deposits and microcracks were found in single-use NiTi instruments. EDS indicated that surface deposits may be dentin.ConclusionThe risk of NiTi rotary instrument fracture in the canal is low when a new instrument is used by experienced endodontists. The most common cause of failure, albeit rare, was shear failure.     

Influence of torque control motors and the operator's proficiency on ProTaper failures

OBJECTIVE: The purpose of this study was to evaluate the influence of 2 electric torque control motors and operator experience with a specific nickel-titanium rotary instrumentation technique on the incidence of deformation and separation of instruments. STUDY DESIGN: ProTaper (PT) nickel-titanium rotary instruments were used at 300 rpm. In the first part of the study, electric high torque control (group 1) and low torque control (group 2) motors were compared. In the second part of the study, 3 operators with varying experience (groups 3, 4, and 5) were also compared. Twenty sets of PT instruments and 100 canals of extracted human molars were used in each group. Each set of PT instruments was used in up to 5 canals and sterilized before each case. For irrigation, 2.5% NaOCl was used. The number of deformed and separated instruments among the groups (within each part of the study) was statistically analyzed for significance with pair-wise comparisons by using the Fisher exact test (alpha =.05). RESULTS: In part 1, instrument deformation and separation did not occur in groups 1 and 2. In part 2, 25 and 12 instruments were deformed and separated, respectively, with the least experienced operator. Instrument deformation and separation did not occur with the most experienced operator. The Fisher exact test revealed a significant difference between groups 3 and 4 with respect to instrument deformation (P =.0296). In addition, the Fisher exact test revealed that the incidence of instrument deformation was statistically different between groups 3 and 5 (P <.0001) and groups 4 and 5 (P =.0018). The incidence of instrument separation was significantly higher in group 5 than in groups 3 and 4 (P =.001). CONCLUSIONS: Preclinical training in the use of the PT technique at 300 rpm is crucial to prevent instrument separation and reduce the incidence of instrument deformation. The use of an electric high torque control motor is safe with the experienced operator.     

Evaluation of single-use rotary nickel-titanium instruments

The purpose of this study was to analyze the number and types of defects observed in single-use, rotary nickel-titanium instruments. Every ProFile Series 29.04 taper nickel-titanium instrument used during a 4-week period in an endodontic specialty practice was collected. All instruments were new and were used by experienced clinicians during a single patient visit. The instruments were routinely used in a crown-down manner with RC Prep lubrication and copious irrigation. The instruments were used in a MicroMega 324 air motor in a 6:1 gear reduction contra-angle at 333 rpm. The instruments were collected, ultrasonically cleaned, sterilized, and inspected at x16 magnification. Torsional, flexural, and fracture defects were recorded and statistical analysis was performed using the Kruskal-Wallis one-way analysis of variance. A total of 786 ProFile Series 29 nickel-titanium rotary instruments were evaluated; 115 (14.63%) showed some type of defect after one clinical use. Size 3 instruments had the highest defect rate (22.66%) followed by size 5 (17.30%), size 2 (17.24%), and size 4 instruments (16.10%). However, there was no statistically significant difference. The size 6 and size 7 instruments showed minimal defects (2.38% and 4.76%, respectfully). Seven of 786 files had fractured (0.891%). There was no statistically significant difference in the type of failure seen within each file size. This study does show that defects can occur even with new files in the hands of experienced endodontists, and for absolute safety a single-use approach should be followed.     

Impact of Heat Treatments on the Fatigue Resistance of Different Rotary Nickel-titanium Instruments

Introduction

The aim of this study was to assess the influence of M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK) and controlled memory technologies on the fatigue resistance of rotary nickel-titanium (NiTi) files by comparing files made using these 2 technologies with conventional NiTi files.

Methods

Files with a similar cross-sectional design and diameter were chosen for the study: new 30/.06 files of the EndoWave (EW; J. Morita Corp, Osaka, Japan), HyFlex (HF; Coltene/Whaledent, Inc, Cuyahoga Falls, OH), ProFile Vortex (PV; Dentsply Tulsa Dental Specialties, Tulsa, OK), and Typhoon (TYP; Clinician's Choice Dental Products, New Milford, CT) systems together with ProTaper Universal F2 instruments (PTU F2; Dentsply Maillefer, Ballaigues, Switzerland). The compositions and transformation temperatures of the instruments were analyzed using x-ray energy-dispersive spectroscopy and differential scanning calorimetry, whereas the mean file diameter values at 3 mm from the tip (D3) were measured using image analysis software. The average number of cycles to failure was determined using a fatigue test device.

Results

X-ray energy-dispersive spectroscopy analysis showed that, on average, all the instruments exhibited the same chemical composition, namely, 51% Ni–49% Ti. The PV, TYP, and HF files exhibited increased transformation temperatures. The PTU F2, PV, and TYP files had similar D3 values, which were less than those of the EW and HF files. The average number of cycles to failure values were 150% higher for the TYP files compared with the PV files and 390% higher for the HF files compared with the EW files.

Conclusions

M-Wire and controlled memory technologies increase the fatigue resistance of rotary NiTi files.     

The deterioration of rotary nickel-titanium files under controlled conditions

It has been shown that rotary nickel-titanium files cannot be used indefinitely. Researchers and clinicians have not been able to agree on how many times a file can be used before being discarded, except if a file has fractured or become visibly distorted. This study used ISO size 20 files of 0.04 taper in the curved canals of extracted mandibular molars. The canals had been previously instrumented to an ISO size 15 with stainless steel hand files. The irrigant used during rotary and hand instrumentation was Glyde. The rotary files were closely examined with scanning electron microscopy before use to detect any defects. They were then reexamined after each of five uses to document deterioration. An electric handpiece was configured to rotate at 150 rpm and secured to the testing device, which also held the extracted tooth. The testing device controlled the load at 8 N, the depth of penetration for each canal and the rate of penetration (12 mm/min). Used instruments demonstrated surface fatigue wear and cracking. Torsional moment at failure was determined on a torsiometer for used and new instruments. Data (n = 10) were analyzed by analysis of variance. The torsional moment for used and new instruments was not affected by use (p = 0.25).     

Effectiveness of nickel-titanium files for preparing curved root canals

Abstract In this study, the effect of 2 different endodontic files on the final shape of curved root canals of extracted single rooted teeth were examined in the scanning electron microscope. The instruments tested were a newly designed nickel-titanium endodontic file and a conventional K-type file. The files were used with in and out linear movements with a circumferential motion starting with a size 15 file. Final preparation of the apical thirds of the canals was performed with a size 35 file. Shaping effectiveness of the tested instruments was evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging. Our observations revealed that more centered and tapered preparations were obtained with the use of the nickel-titanium files than with the conventional K-type files.     

Current Challenges and Concepts of the Thermomechanical Treatment of Nickel-Titanium Instruments

IntroductionThe performance and mechanical properties of nickel-titanium (NiTi) instruments are influenced by factors such as cross-section, flute design, raw material, and manufacturing processes. Many improvements have been proposed by manufacturers during the past decade to provide clinicians with safer and more efficient instruments.MethodsThe mechanical performance of NiTi alloys is sensitive to their microstructure and associated thermomechanical treatment history. Heat treatment or thermal processing is one of the most fundamental approaches toward adjusting the transition temperature in NiTi alloy, which affects the fatigue resistance of NiTi endodontic files. The newly developed NiTi instruments made from controlled memory wire, M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK), or R-phase wire represent the next generation of NiTi alloys with improved flexibility and fatigue resistance. The advantages of NiTi files for canal cleaning and shaping are decreased canal transportation and ledging, a reduced risk of file fracture, and faster and more efficient instrumentation. The clinician must understand the nature of different NiTi raw materials and their impact on instrument performance because many new instruments are introduced on a regular basis.ResultsThis review summarizes the metallurgical properties of next-generation NiTi instruments, the impact of thermomechanical treatment on instrument flexibility, and the resistance to cyclic fatigue and torsion.ConclusionsThe aim of this review was to provide clinicians with the knowledge necessary for evidence-based practices, maximizing the benefits from the selection and application of NiTi rotary instruments for root canal treatment.     

Effect of rotational speed on the breakage of nickel-titanium rotary files

Nickel-titanium 0.04-tapered rotary files were evaluated for breakage at different rotational speeds in semicircular bovine bone simulated root canals of identical size and radius for each file size group tested. The bovine bone canals had a radius of curvature of 5 mm and a canal width equivalent to the D1 diameter of the file plus 0.04 mm. Profile instrument #3, #4, and #5 were tested at 150, 250, and 350 rpm. A contra-angle electric handpiece was mounted on an Instron machine that was set to deliver a constant downward speed of 5 mm/min. The electric handpiece and Instron machine were activated until the files broke. The amount of file tip penetration into the semicircular bovine bone canal was measured in degrees with a protractor from a radiographic image taken of the file inside the bone model. Greater degrees of tip penetration indicated greater resistance to breakage. Statistical analysis was done and the results indicated that there was a significant difference for all file sizes in the extent of file tip penetration before breakage. In the rotation range between 150 and 350 rpm the greatest extent of penetration occurred at 150 rpm. This study concluded that 0.04 taper nickel-titanium rotary file breakage is less likely to occur if the files are rotated at lower speeds.     

Fatigue resistance of engine-driven rotary nickel-titanium instruments produced by new manufacturing methods

The aim of the present study was to investigate whether cyclic fatigue resistance is increased for nickel-titanium instruments manufactured by using new processes. This was evaluated by comparing instruments produced by using the twisted method (TF; SybronEndo, Orange, CA) and those using the M-wire alloy (GTX; Dentsply Tulsa-Dental Specialties, Tulsa, OK) with instruments produced by a traditional NiTi grinding process (K3, SybronEndo). Tests were performed with a specific cyclic fatigue device that evaluated cycles to failure of rotary instruments inside curved artificial canals. Results indicated that size 06-25 TF instruments showed a significant increase (p < 0.05) in the mean number of cycles to failure when compared with size 06-25 K3 files. Size 06-20 K3 instruments showed no significant increase (p > 0.05) in the mean number of cycles to failure when compared with size 06-20 GT series X instruments. The new manufacturing process produced nickel-titanium rotary files (TF) significantly more resistant to fatigue than instruments produced with the traditional NiTi grinding process. Instruments produced with M-wire (GTX) were not found to be more resistant to fatigue than instruments produced with the traditional NiTi grinding process.     

Machining efficiency of nickel-titanium K-type files in a linear motion

The purpose of this study was to compare, in vitro, the machining efficiency of four brands of nickel-titanium files and two brands of stainless steel K-type files. Instruments sizes 15 to 40 were tested in a linear motion simulating the clinical motion used to remove a file from the canal. The tips of the loaded files were in contact with a resin block. The load applied increased with file size. An indentation varnish caliper was used to measure the depth of the groove after 100 back-and-forward motions. The stainless steel instruments with a triangular cross-section were more efficient than the stainless steel instruments with a square cross-section. There was a significant discrepancy between the machining ability of the nickel-titanium K files. The Maillefer instruments were the most efficient.     

Failure of ProFile instruments used with air, high torque control, and low torque control motors.

OBJECTIVE: The purpose of this study was to evaluate the influence of 350-rpm rotational speed on the failure incidence of ProFile nickel-titanium rotary instruments (PRI) when used by an experienced operator in conjunction with different motors. STUDY DESIGN: Extracted human mandibular and maxillary first and second molars demonstrating curvatures greater than 25 degrees were used. PRI sizes 40 to 15 and with 0.06 taper were used in crown-down fashion at 350 rpm. In groups 1 through 4, air, high torque control, low torque control, and very low torque control motors were used, respectively. Each group included 30 canals. One set of PRI was used for each canal. Before each use the PRI set was sterilized by steam autoclave. The canals were enlarged until a size 25 PRI reached the working length. A 2.5 x magnification was used to check for instrument deformation after each passage. The number of deformed and separated instruments was recorded for the various experimental groups. RESULTS: Instrument deformation and separation did not occur in any of the 4 groups. CONCLUSIONS: The results suggested that the use of PRI in conjunction with the different motors by an experienced operator in a crown-down manner at 350 rpm is safe.     

Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments.

The absence of adequate testing standards for engine-driven nickel-titanium (NiTi) instruments necessitates further study of these instruments in all areas. This study examined three groups of engine-driven rotary NiTi endodontic instruments (Profile, Hero, and Quantec) and assessed the times for dynamic fracture in relation to the radius of curvature to which the instruments were subjected during preparation, with the instrument diameter determined by size and taper and the mode by which the fracture occurred. Ten instruments were randomly selected representing each size and taper for each group and for each radius of curvature: 600 in total. The instruments were rotated at 350 rpm and introduced into a tempered steel curve that simulated a canal. Two radii of curvature of canals were used: 5 and 10 mm. Time at fracture was noted for all files, and the fracture faces of each file were analyzed with scanning electron microscopy. Radius of curvature was found to be the most significant factor in determining the fatigue resistance of the files. As radius of curvature decreased, fracture time decreased. Taper of files was found to be significant in determining fracture time. As diameter increased, fracture time decreased. In all cases, fracture was found to be of a ductile nature, thus implicating cyclic fatigue as a major cause of failure and necessitating further analyses and setting of standards in this area.     

Effect of clinical use on the cyclic fatigue resistance of ProTaper nickel-titanium rotary instruments

The resistance of ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) nickel-titanium rotary instruments to cyclic fatigue was examined after their initial use in straight or curved canals in vivo. These instruments were rotated freely inside a steel phantom until separation. The number of rotations before failure and the lengths of the separated fragments were compared with data derived from new instruments under the same experimental setup (n = 20). With the exception of F1 and F3, instruments previously used in curved canals were more susceptible to cyclic fatigue than those previously used in straight canals (p < 0.05). Separation occurred predominantly at the D10 to D12 level. For the F series, a negative correlation (p < 0.05) was observed between the number of rotations before failure and the file diameters at their separation levels. ProTaper F3 instruments are highly susceptible to cyclic fatigue failure and should be reused with caution irrespective of whether they are initially used for shaping straight or curved canals.     

The shaping effects of three nickel-titanium rotary instruments in simulated S-shaped canals

The purpose of this study was to compare the shaping effects of three nickel-titanium rotary instruments, ProTaper, K3, and RaCe, with emphasis on canal transportation. Simulated canals with an S-shaped curvature in clear resin blocks were prepared with a torque-control, low-speed engine. Canals were prepared using the crown-down technique to the size of #30. Canal aberrations were assessed by comparing the pre- and postinstrumentation images under a stereomicroscope. ProTaper instruments caused greater widening of canals compared to K3 or RaCe. Furthermore, ProTaper files showed a tendency to ledge or zip formation at the end-point of preparation. These canal aberrations may be caused by ProTaper finishing files, which appear to be less flexible than other files of the same tip-size, because of their greater taper-size. These results suggest that nickel-titanium file systems including less tapered, more flexible instruments, like K3 and RaCe should be used in the apical preparation of canals with a complicated curvature.