Defects in ProTaper S1 instruments after clinical use: longitudinal examination

A New Methodology to Determine the Orifice for Root Canal Configurations in First Permanent Molar Root and Canal Morphologies Using Micro-Computed Tomography

BACKGROUND

The distinction between where the pulp chamber ends and the root canal system begins is poorly defined within the existing literature.

METHODS

This paper aimed to describe a range of accurate methods to define the transition from pulp chamber to root canal in different first molar root morphologies using micro-focus computed tomography (micro-CT).

METHODS

The sample consisted of 86 mandibular and 101 maxillary first molars from the skeletal collections housed in the Department of Anatomy and Histology of the Sefako Makgatho Health Sciences University and the Pretoria Bone Collection. A stepwise approach using the cemento-enamel junction (CEJ) and dedicated landmarks was followed to create an automated cross-sectional slice.

RESULTS

Transition from pulp chamber to root canal could be accurately determined on maxillary and mandibular teeth. The occurrence of two separate roots in mandibular molars was 97.7%, with the remaining 2.3% having an additional disto-lingual root, with no mandibular molars displaying fused roots. In the maxillary molars, 92.1% had three separate roots and 7.9% displayed root fusion. Within this group, one tooth displayed a C-shaped root canal configuration and one a mesotaurodont-type morphology.

CONCLUSION

The suggested methodology to determine orifice location was found to be appropriate in all morphological types.

Effect of different axial speed patterns on cyclic fatigue resistance of rotary nickel-titanium instruments

BACKGROUND

To evaluate the effect of pecking motions with faster upward speed on the dynamic cyclic fatigue resistance of nickel-titanium rotary instruments with different metallurgy.

METHODS

Forty each of ProTaper Universal F3 (PTU) and ProTaper Gold F3 (PTG) instruments (size #30/.09) were equally divided into four groups. The test was performed using an 18-mm-long stainless steel artificial canal with a 5-mm radius of curvature, a 45° canal curvature and a 2-mm canal diameter. A downward speed of 100 mm/min was employed, while the upward speed was set at 100, 150, 200 or 300 mm/min. Time to failure (Tf), number of cycles to failure (Nf) and number of pecking motions to failure (Np) were recorded. Statistical analysis was performed using Kruskal Wallis and Mann-Whitney U tests for Tf, Nf, and Np (α = 0.05).

RESULTS

The 100/300 mm/min group showed significantly higher Np values than the 100/100 mm/min group (p < 0.05), whereas there were no significant differences in Tf and Nf among the tested speed groups (p < 0.05) in either PTU or PTG. PTG exhibited significantly higher Tf, Nf, and Np than PTU (p < 0.05).

CONCLUSIONS

Under the tested conditions, the fastest upward speed group showed significantly higher cyclic fatigue resistance, as demonstrated by larger Np, than the same speed group. PTG had significantly higher cyclic fatigue resistance than PTU in all groups.

Fatigue Analysis of NiTi Rotary Endodontic Files through Finite Element Simulation: Effect of Root Canal Geometry on Fatigue Life

This article describes a numerical procedure for estimating the fatigue life of NiTi endodontic rotary files. An enhanced finite element model reproducing the interaction of the endodontic file rotating inside the root canal was developed, which includes important phenomena that allowed increasing the degree of realism of the simulation. A method based on the critical plane approach was proposed for extracting significant strain results from finite element analysis, which were used in combination with the Coffin-Manson relation to predict the fatigue life of the NiTi rotary files. The proposed procedure is illustrated with several numerical examples in which different combinations of endodontic rotary files and root canal geometries were investigated. By using these analyses, the effect of the radius of curvature and the angle of curvature of the root canal on the fatigue life of the rotary files was analysed. The results confirm the significant influence of the root canal geometry on the fatigue life of the NiTi rotary files and reveal the higher importance of the radius of curvature with respect to the angle of curvature of the root canal.

Defects and Safety of NiTi Root Canal Instruments: A Systematic Review and Meta-Analysis

Aim: To review the reported defect and fracture rates of various NiTi instrumentation systems and identify factors that may influence the chance of NiTi file separation clinically.

Data Sources: PubMed, EMBASE, and SCOPUS with controlled vocabulary and keywords in various combinations to identify articles that reported on the defects and/or fracture of NiTi instrument used clinically (Jan 1980 till Aug 2021), with additional search manually by going through the list of references of the initially screened articles. Those satisfying the inclusion and exclusion criteria were entered into the analysis.

Study Eligibility Criteria, Participants, and Interventions: All studies from the said databases reporting on NiTi root canal instruments that were deformed or separated during normal clinical use.

Study Appraisal and Synthesis Methods: Studies with data available and suitable for meta-analysis were grouped according to the general design of the NiTi instruments for comparison. Safety quotient value was calculated based on the rate of instrument distortion and fracture.

Results: Various instrument designs exhibited different incidences of distortion and fracture, hence a different “safety quotient” (ratio of the amount of deformed instruments to that of fractures in use). Heat-treated files showed the highest safety quotient value. All brands of NiTi file demonstrated a statistically significantly lower incidence of fracture, if treated as disposable instruments after clinical use in a patient.

Limitations: Inclusion of articles written in English only, and grouping of file systems into general design types in the analysis.

Conclusions and Implications of Key Findings: NiTi endodontic files should be scrutinized for defects before being used in the root canal. Disposing the NiTi instruments after clinical use in a patient (so-called “single use”) is recommended for minimizing fracture clinically. Certain instrument designs tend to show discernible deformation before they should fracture in the next use.

Cyclic Fatigue Resistance of Blue Heat-Treated Instruments at Different Temperatures

The main aim is to evaluate the cyclic fatigue resistance of blue heat-treated instruments with different kinematics. Twenty-four endodontic instruments of the same brand were used for each of three experimental groups: VB (Vortex Blue 40/0.04), RB (RECIPROC Blue 40/0.06), and XB (X1 Blue 40/0.06). The instruments were randomly distributed and subjected to temperatures of 20°C and 37°C. The fatigue test was performed using a stainless steel device. Data were analysed using the Shapiro-Wilk test, Student's t-test, the F test, and Tukey's and Tamhane tests at significance level P=0.05. The instruments' cyclic fatigue resistance at both temperatures differed significantly for each instrument type (P < 0.001). The RB instruments displayed greater cyclic fatigue resistance at the tested temperatures compared with the VB and XB instruments (P < 0.001). Reciprocating kinematics positively influenced cyclic fatigue resistance. Blue heat-treated instruments showed decreased cyclic fatigue resistance as the temperature increased (P < 0.001).

Impact of Peracetic Acid on the Dynamic Cyclic Fatigue of Heat-Treated Nickel-Titanium Rotary Endodontic Instrument

Peracetic acid (PAA) is widely used as a sterilizing/disinfecting agent, and, in endodontics, it has been introduced as a promising irrigant in root canal treatment. It has been used at different concentrations to achieve various functions. However, endodontic instruments in contact with PAA of a certain concentration may affect their fatigue resistance. Therefore, the aim of this study was to investigate the impact of PAA on the cyclic fatigue resistance of three commercial heat-treated nickel-titanium (NiTi) rotary files. Three types of heat-treated NiTi rotary files were selected: One Curve (OC), ProTaper Gold (PTG), and Wave One Gold (WOG). Each type was divided into three subgroups (n = 6 for each file type): (1) untreated instruments; (2) files immersed in 0.002% PAA; and (3) files immersed in 0.35% PAA. The performance of each file type was tested in a simulated canal. The number of cycles to fracture (NCF) was determined to assess cyclic fatigue resistance of the files. Independent sample t-test was applied to compare each treated file within a subgroup with its respective control group, and one-way ANOVA was used for comparison among the main groups. All types of tested files revealed a significant decline in the cyclic fatigue resistance after exposure to 0.002% PAA except the PTG (P=0.209). After exposure of the files to a higher concentration (0.35% PAA), a dramatic reduction was demonstrated by all the groups. Before and after exposure of the files to PAA, PTG displayed the highest cyclic fatigue resistance, followed by the WOG, while the OC showed the lowest resistance. Exposure of heated-treated NiTi files to PAA in a relatively high or low concentration adversely affects the cyclic fatigue resistance. The PTG files demonstrated the best performance among the tested types and can be disinfected with 0.002% PAA for clinical purpose.

Clinical fracture incidence of rotary and reciprocating NiTi files: A systematic review and meta-regression

This systematic review was registered in PROSPERO (CRD42017075917) and aimed to investigate whether the available clinical evidence supports the hypothesis that reciprocating motion results in a lower incidence of nickel-titanium files fracture compared to continuous rotation. Clinical studies that reported the incidence of fracture of engine-driven nickel-titanium files were included. The main exposure was the kinematics, and the primary outcome was the incidence of files fracture. The overall incidence of files fracture was 2.27%, with a trend for higher incidence with rotary motion (2.43%) than with reciprocating (1.0%), though without significant differences. Multiple meta-regression models revealed that the use of nickel-titanium files in more than four teeth and less proficient operators were associated with a higher incidence of file fracture. There was no difference in the clinical incidence of fracture of nickel-titanium instruments between reciprocating and rotary motions; however, other factors were identified.

Fractographic analysis of separated endodontic file designs

Endodontic rotary files are cutting instruments used to perform root canal procedures within a tooth interior. Focusing on quantitative fractographic analysis increases necessary, clinical performance understanding of file separation failure. This research employed controlled, dynamic testing to failure of commercial rotary files, analyzing the fractographic, forensic characteristics in relation to Weibull reliability determination, considering: (1) design analysis; (2) stress concentrations; (3) times to failure; (4) number of cycles to failure (NCF). Ex vivo testing included three file designs, each having constant tip size (0.035 mm), taper (0.06 mm/mm), and length (25 mm). Files were individually tested using an electric, torque-controlled handpiece, rotating within a standardized, simulated canal until fracture separation occurred. Fractographic analysis, including critical measurements, was conducted using the scanning electron microscope (SEM) (PhenomProX, PhenomWorld, NL). Weibull statistical analysis established reliability factors per design group. Fractographic analysis identified separation fractures, processing inclusions, flexural-fatigue striations, and stress concentrations at flute pitches. Calculated NCF median values (1277-EE; 899-VB; 713-PI) demonstrated significant statistical differences among groups (p < 0.001). Separated apical fragments yielded statistically significant differences (p ≤ 0.05) for varying file design groups. Weibull moduli among groups were statistically equivalent. Fractographic analysis exposed a presence of multiple failure factors in addition to defect distribution, governing cyclic fatigue failure originating at stress concentration points irrespective of file design. Fractographic analysis indicated that a change in file design, specifically at the working edges, in addition to improved surface finish, has the potential of reducing failures by lowering points of stress concentration and reducing fracture initiating surface cracks.

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

Objectives

This systematic review evaluated the influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) instruments.

Materials and Methods

A systematic search without restrictions was conducted in the following electronic databases: PubMed, Scopus, Web of Science, ScienceDirect, Cochrane, and Open Grey. The hand search was also performed in the main endodontic journals. The eligible studies were submitted to the methodological assessment and data extraction.

Results

From 203 abstracts, a total of 10 articles matched the eligible criteria. After reading the full articles, 2 were excluded because of the absence of the heat-treated instruments in the experimental design and 3 due to the lack of a control group using heat-treated instruments without autoclave sterilization. From the 5 included studies, 1 presented a low risk of bias, 3 presented moderate and 1 high risk. It was observed heterogeneous findings in the included studies, with autoclave sterilization cycles increasing, decreasing or not affecting the cyclic fatigue life of heat-treated NiTi instruments. However, the retrieved studies evaluating the cyclic fatigue resistance of endodontic instruments presented different protocols and assessing outcomes, this variability makes the findings less comparable within and also between groups and preclude the establishment of an unbiased scientific evidence base.

Conclusions

Considering the little scientific evidence and considerable risk of bias, it is still possible to conclude that autoclave sterilization procedures appear to influence the cyclic fatigue resistance of heat-treated NiTi instruments.

Removal of a separated endodontic instrument by using the modified hollow tube-based extractor system: A case report

The frequency of separation of NiTi rotary instruments has increased with the increasing use of these instruments, and this error may result from inadequate experience of using these instruments. This iatrogenic error can complicate root canal treatment, and special experience is required to manage this problem. This case report describes the management of the separation of an F3 instrument from a ProTaper NiTi rotary system. A 30-year-old man was referred to the College of Dentistry, Taibah University (Saudi Arabia) with an intracanal separated NiTi rotary instrument (F3 of the ProTaper system; Dentsply Maillefer, Ballaigues, Switzerland) in the canal of the maxillary right canine. The separated instrument was removed by using the modified hollow tube–based extractor system. The present case revealed that sometimes a simple method can be an effective alternative of a professional method; using NiTi rotary instruments with strict adherence is important for the prevention of instrument separation.

Cyclic Fatigue Resistance of Nickel-titanium Rotary Instruments according to the Angle of File Access and Radius of Root Canal

INTRODUCTION

The aim of this study was to compare the influences from different access angles and curvature radii on cyclic fatigue resistance of nickel-titanium rotary files.

METHODS

Two file systems (2Shape [TS; MicroMega, Besançon, France] and HyFlex CM [HCM; Coltène/Whaledent, Allstätten, Switzerland]) were used. A total of 192 instruments of TS #25/.04 (TS1), TS #25/.06 (TS2), HCM #25/.04, and HCM #25/.06 were evaluated at 3 insertion angles (0°, 10°, and 20°) and 2 radii (5 mm and 3 mm) in 16-mm stainless steel artificial canals with a 60° curvature. Cyclic fatigue resistance was determined by the number of cycles to failure (NCF) using a customized testing device. Data were analyzed statistically with the significance level established at 95%.

RESULTS

In the 3-mm radius canal, the instruments showed lower cyclic fatigue resistance than in the 5-mm radius canal (P < .05). HCM #25/.06 and all .04 taper instruments had a significant NCF reduction at 20° and 10° in the 3-mm radius canal (P < .05), whereas TS2 showed no significant differences. In the 5-mm radius of curvature, although .06 taper instruments had no significant NCF reduction for each angle tested, .04 taper files exhibited significant NCF reduction when tested at 20° (P < .05). Comparing the same size instruments, HCM had higher NCF than TS (P < .05). Instruments with a .04 taper exhibited higher NCF than the .06 ones with the same heat treatment (P < .05).

CONCLUSIONS

An inclined insertion into the canals decreased cyclic fatigue resistance of thermal-treated instruments with a .04 taper at all radii of curvature tested. The synergistic effect of a small radius of curvature and access angulation of heat-treated instruments decreases their fatigue resistance.

Factors influencing incidents of complications while using nickel-titanium rotary instruments for root canal treatment

Background

To investigate the complications associated with the use of nickel titanium rotary instruments (NiTi-RIs) for root canal treatments (RCTs), in Saudi Arabia dental practice, and to explore the influencing factors.

Methods

After obtaining an ethical approval, two pilot studies were conducted to formulate the final questionnaire. The sample size was measured taking into consideration 60% expected response rates and confidence level of 99.9%. The questionnaire was emailed to 600 general dentists (GDs) randomly selected from the dental register and all of the endodontists (175). The email’s introduction clarified objectives of the study and guaranteed that all of the collected information would remain confidential. A reminder was sent after 10 weeks. The data were collected and analyzed using the chi-squared test at a 0.05 significance level.

Results

With a 51% overall response rate, 71.9% off the respondents used NiTi-RIs. The majority (83.1%) experienced complications while using NiTi-RIs; with the instruments’ fracture being significantly the most common complication (52.7%) (p < 0.001). The majority (87.7%) experienced NiTi-RIs’ fractureat least once; with more endodontists (94.3%) than GDs (83.3%) (p < 0.001). The greater the number of weekly performed RCTs and participants’ experiences, the more NiTi-RIs fractures and the greater the number of fracture incidents (p < 0.001). While 60% of those who performed 1–3 RCTs per week experienced NiTi-RIs fractures, 100% of those who performed more than 12 RCTs per week did so. The highest percentage of those who experienced more than 10 fractured NiTi-RIs (60%) was within the group who performed more than 12 RCTs per week. Although fracture incidents decreased with a smaller number of reuses, there was no significant correlation between the number of fractured instruments and NiTi-RIs discard strategy (p ≥ 0.05).

Conclusion

Fracture incidence was the most common complication while using NiTi-RIs, regardless of the clinicians’ experiences and skills. While the single use may reduce NiTi-RIs fractures, to some extent, the greater number of RCTs performed per week was the most influential factor.

Microcomputed tomographic investigation of the trepan bur/microtube technique for the removal of fractured instruments from root canals without a dental operating microscope

OBJECTIVES

The aim of this study was to evaluate the removal of fractured instruments in mandibular incisor canals by using the trepan bur/microtube technique without a dental operating microscope (DOM).

MATERIALS AND METHODS

Thirty-four mandibular incisors were selected, and 5-mm apical segments of #25/.06 taper K3 NiTi instruments were fractured in the apical portion of each canal. Coronal enlargement was performed, and a staging platform was prepared at the coronal aspect of the fractured instrument. Then, a trepan bur was used to expose 1-1.5 mm of the fragmented instrument, and a microtube device was used to withdraw the fragment. Microcomputed tomographic (micro-CT) imaging was used to evaluate the geometric changes in the root canal and dentin. The time required for fractured instrument removal in each sample was recorded, and the results were statistically analyzed with a paired t test.

RESULTS

The trepan bur/microtube technique exhibited a success rate of 76.47%, and the average fractured instrument removal time was 8.55 ± 5.81 min. The changes in canal volume and dentin volume from the coronal end of the fractured instrument to 1.5 mm apical to the end were significantly greater than those from the cementoenamel junction (CEJ) to the coronal end of the fractured instrument during fractured instrument removal (P < 0.0001).

CONCLUSIONS

The study showed that the trepan bur/microtube technique had a significant impact on geometric changes in the root canal and dentin from the coronal end of the fractured instrument to 1.5 mm apical to the end.

CLINICAL RELEVANCE

These findings suggest that the trepan bur/microtube technique may be an optional method for fractured instrument removal from relatively straight canals.

A critical appraisal of studies on cyclic fatigue resistance of engine-driven endodontic instruments

The endodontic literature contains a plethora of studies on static and dynamic cyclic fatigue resistance tests performed on a large array of rotary or reciprocating nickel-titanium endodontic instruments. It was the aim of this review to summarize the currently available evidence to point out the different outcomes from static versus dynamic tests and to assess whether cyclic fatigue tests provide useful data and information for clinical practice. An electronic literature research in the database PubMed was performed using appropriate search terms, and the titles and abstract were screened for relevance. Language was restricted to English. The review reveals marked differences between the results obtained in static and dynamic tests, and also, the results for the same instruments assessed either under static or dynamic experimental conditions are widely inconsistent. Between the lowest and the highest value for one and the same pathfinding instrument was a factor of about 123 when cyclic fatigue was assessed either under static or dynamic experimental conditions. Moreover, standard deviations of up to 30% have been reported. Environmental temperature has a 500% impact on the lifetime of instruments. In conclusion, fatigue resistance tests conducted under room temperature should be regarded as having little meaning and the scientific and clinical benefits of fatigue resistance tests are very limited. These data should be provided by the manufacturer of the instruments.

Cyclic fatigue resistance of rotary NiTi instruments produced with four different manufacturing methods

The aim of this study was to compare the cyclic fatigue resistance of rotary NiTi files, produced with four different manufacturing methods on specially designed dynamic models that simulated clinical conditions. In this study, 120 files, consisting of 30 files for Typhoon, ProTaper Next, RaCe, and Twisted Files nickel titanium rotary systems were used. The 30 files of each group were divided into three subgroups to be used in artificial canals with a 60° angle of curvature and radii of curvature of 2, 5, and 8 mm (n = 10). All files were rotated in the artificial canals until fracture occurred and the number of cycles to fracture was calculated. The data were analyzed using one- and two-way analyses of variance and Tamhane multiple comparison tests. In all three groups, Typhoon instruments had the highest number of cycles to failure than the RaCe, ProTaper Next, and Twisted Files instruments, and the difference statistically significant (p < .05). There were no significant differences between the RaCe, ProTaper Next, and Twisted Files groups (p > .05). The CM wire Typhoon system was significantly more resistant to cyclic fatigue compared to the other file systems in all three artificial canals. When the fracture resistance of an instrument in three different artificial canals was compared, the mean NCFs decreased as the radius of the curvature of the canal decreased from 8 to 2 mm. Manufacturing method is one of the most important factors on cyclic fatigue resistance, also the radius of curvature effects the cyclic fatigue.

A comparative evaluation of cyclic fatigue resistance for different endodontic NiTi rotary files: An in-vitro study

Aim

This in-vitro study evaluated and compared the flexural fatigue resistance for Hero Shapers, Hyflex CM, One Shape, Profile Vortex and Protaper Next rotary NiTi files.

Method and materials

Total 25 rotary NiTi files allocated to each experimental group were tested in a simulated constructed apparatus with an angle of curvature 60° & radius of curvature 5 mm. Each experimental file was coated with EDTA gel and was placed in endodomotor handpiece with rubber stopper at support steel cylinder and its end between two shaping steel cylinders on the simulated apparatus. File was then rotated at 400 rpm, 2.5 N/cm torque and simultaneously digital stop watch was started. Time taken (in seconds) until the file got fractured was recorded.

Results

Time taken to fracture ranged from 7 to 58 s in different groups. Analysis of variance show a statistically significant intergroup difference (p < 0.001). Tukey HSD test showed the significant differences. The Weibull modulus values ranged from 7.31 to 24.19.

Conclusion

Cyclic flexural fatigue resistance was observed highest for Grp IV (Hyflex CM) and lowest for Grp I (Hero Shapers).

Clinical significance

Hyflex CM rotary NiTi files can be used in curved root canals as they had superior resistance and long survival time which will be helpful in eliminating one of the reasons for file fracture (due to cyclic flexural fatigue) during the root canal treatment clinically where root canal possesses a sharp bend or curve.

An analysis of cyclic fatigue resistance of reciprocating instruments in different canal curvatures after immersion in sodium hypochlorite and autoclaving: An in vitro study

Aim

The aim of this study is to assess the effect of sodium hypochlorite and sterilization on the cyclic fatigue resistance of two reciprocating nickel-titanium files using a rotary and a reciprocating motor.

Materials and Methods

Totally, 160 Reciproc and Wave One files were tested. The eighty files of the same brand were assigned into four groups (n = 20). These four groups were further divided into two subgroups, 1a and 1b, 2a and 2b, 3a and 3b, 4a and 4b consisting of ten files in each group. 2.5% NaOCl for 5 min, 2.5% NaOCl for 5 min + 1 cycle of autoclave sterilization, 2.5% NaOCl for 5 min + 5 cycles of autoclave sterilization, no sterilization (control). Groups 1a, 2a, 3a, and 4a were subjected to 30° and Groups 1b, 2b, 3b, and 4b were subjected to 60° canal curvature.

Results

Intergroup comparison reveals that there is an increase in cyclic fatigue resistance from the first cycle to the fifth cycle of autoclave which is statistically significant.

Conclusion

Reciproc and Wave One showed reduced cyclic fatigue resistance on immersion in NaOCl for 5 min. Multiple autoclaving cycles significantly increased the cyclic fatigue resistance of Reciproc file system in both the curvatures. There was a decrease in cyclic fatigue resistance for Wave One after multiple autoclaving at 60° curvature which was statistically significant.

The effects of autoclave sterilization on the cyclic fatigue resistance of ProTaper Universal, ProTaper Next, and ProTaper Gold nickel-titanium instruments

Objectives

It was aimed to compare the cyclic fatigue resistances of ProTaper Universal (PTU), ProTaper Next (PTN), and ProTaper Gold (PTG) and the effects of sterilization by autoclave on the cyclic fatigue life of nickel-titanium (NiTi) instruments.

Materials and Methods

Eighty PTU, 80 PTN, and 80 PTG were included to the present study. Files were tested in a simulated canal. Each brand of the NiTi files were divided into 4 subgroups: group 1, as received condition; group 2, pre-sterilized instruments exposed to 10 times sterilization by autoclave; group 3, instruments tested were sterilized after being exposed to 25%, 50%, and 75% of the mean cycles to failure, then cycled fatigue test was performed; group 4, instruments exposed to the same experiment with group 3 without sterilization. The number of cycles to failure (NCF) was calculated. The data was statistically analyzed by using one-way analysis of variance and post hoc Tukey tests.

Results

PTG showed significantly higher NCF than PTU and PTN in group 1 (p < 0.05). Sterilization significantly increased the NCF of PTN and PTG (p < 0.05) in group 2. PTN in group 3 had significantly higher cyclic fatigue resistance than PTN group 4 (p < 0.05). Also, significantly higher NCF was observed for PTG in group 2 than in groups 3 and 4 (p < 0.05).

Conclusions

PTG instrument made of new gold alloy was more resistant to fatigue failure than PTN and PTU. Autoclaving increased the cyclic fatigue resistances of PTN and PTG.

Influence of Continuous or Reciprocating Optimum Torque Reverse Motion on Cyclic Fatigue Resistance of Two Single-File Nickel-Titanium Rotary Instruments

Objective:

Different single-file instruments and kinematics have been introduced on the market. It is important to know the cyclic fatigue performance of these instruments in these new kinematics such as reciprocation of Optimum Torque Reverse (OTR) motion. The aim of this study was to evaluate the resistance to cyclic fatigue of F6 SkyTaper and OneShape used in continuous rotation (proper rotation) or in reciprocating OTR motion.

Methods:

A total of forty-eight nickel-titanium files were tested. Twenty-four instruments of both brands were divided into two groups (n=12) on the basis of the motion tested: continuous rotation (group 1) or reciprocating OTR motion (group 2). Resistance to cyclic fatigue was determined by recording time to fracture (TtF) in a stainless steel artificial canal with a 60° angle of curvature and 5 mm radius of curvature. Data were analysed by two-way analysis of variance and post-hoc Bonferroni tests for multiple comparisons with P<0.05 as the level of significance.

Results:

F6 SkyTaper showed higher TtF compared with OneShape, both in continuous and in OTR motion (P<0.0001). The two tested instruments showed higher cyclic fatigue resistance in reciprocating OTR motion than continuous rotation (P<0.0001).

Conclusion:

OTR motion significantly improves cyclic fatigue resistance of the tested instruments. In addition, F6 SkyTaper showed higher cyclic fatigue resistance than OneShape in both motions.

Deformation and fracture incidence of Reciproc instruments: a clinical evaluation

AIM

To investigate the incidence of fracture and deformation observed on Reciproc instruments after clinical use.

METHODOLOGY

A total of 1696 Reciproc NiTi instruments that were discarded after normal clinical usage over 30 months were collected. Of these 1580 instruments were R25 (93%), 76 were R40 (5%), and 40 were R50 (2%). The treatments included 3780 root canal preparations, 3023 primary treatments and 757 retreatments. Root canal preparation was standardized and followed the manufacturer's directions for the use of Reciproc files without creating prior glide path with hand instruments. In retreatment cases, Reciproc R25 instrument was used to remove all filling material and to complete the preparation. Each instrument was used for shaping only one tooth. All the instruments used were inspected under a microscope to detect signs of fracture or deformation and, if any fracture existed, the length of the files was measured. Data were analysed using a chi-square test with a level of significance set at P < .05.

RESULTS

A total of 8 Reciproc R25 instruments fractured during treatment, which represents 0.47% of the number of instruments used and 0.21% of the root canals treated. Five instruments fractured in primary treatment cases and three instruments during retreatments. Six Reciproc R25 deformed during clinical use (0.35% of the number of instruments used and 0.15% of the root canals treated), four during retreatments and two during primary treatments. The deformation reported was unwinding of the blades, one at 1 mm from the tip and five between 2 and 3 mm from the tip. No deformations or fracture were registered for the Reciproc R40 and R50 instruments.

CONCLUSIONS

Root canal instrumentation following the manufacturer's instructions can be performed with Reciproc instruments with a very low incidence of instrument fracture and deformation.

Influence of combined cyclic fatigue and torsional stress on the fracture point of nickel-titanium rotary instruments

INTRODUCTION

The combined influence of cyclic fatigue and torsional stress on rotary nickel-titanium instruments has been little investigated. The aim of this study was to determine possible differences in the fracture point of rotary nickel-titanium instruments depending on the application of cyclic fatigue only (CO) or in combination with torsional stress (CT).

METHODS

A novel custom-designed testing device was constructed. The device used a 2-pin design to test files under cyclic fatigue stress and allowed the additional application of defined torsional stress to the lateral aspect of the file by cutting into a dentin block. Files were tested dynamically at an amplitude of 2 mm at 0.0625 Hz using a programmable computer-controlled system. Three rotary NiTi systems were tested at 30° under CO or CT (with an added 1-Ncm torsional load): Revo-S (Micro-Mega, Besancon, France), Vortex (Dentsply, York, PA), and Profile (Dentsply) of tip sizes 25 and 35. For each file type, 10 new files 25 mm in length with a 0.04 taper size were tested. A total of 120 files were tested: 60 for CO and 60 for CT. The mean fragment length (MFL [in millimeters from the shaft to the fracture point]) was measured under 10× magnification with an electronic gauge to assess the location of the fracture. One-way analysis of variance, the Tukey Honestly Significant Differenct (HSD) test, and the Student's t test for paired samples were used for statistical analysis.

RESULTS

All fractures, regardless if CO or CT was used, occurred within the area of the curvature. The addition of a torsional load (CT) resulted in a mean 1.09-mm statistically significant difference between CO and CT (P < .0001, CO MFL = 17.78 mm [standard deviation ± 1.08 mm, n = 60]; CT MFL = 16.69 mm [SD ± 0.54 mm, n = 60]), relocating the fracture point toward the area where torsional load was applied. There was a statistically significant difference between the 3 file systems when they were tested either in the CO mode (P < .01) or the CT mode (P < .05). Statistically significant differences also existed for both instrument sizes (ie, 25 [P < .01] and 35 [P < .0001]).

CONCLUSIONS

CT compared with CO resulted in statistically significantly different MFLs. All fractures remained within the area of the curvature, but with the addition of a torsional load, the location of the fracture moved in the direction of the additionally applied torsional stress. This suggests that stress was distributed from the area in which the torsional load was applied toward the area undergoing cyclic fatigue.

Instrument fracture in root canals - where, why, when and what? A study from a student clinic

AIM

To investigate the incidence of instrument fracture during nonsurgical root canal treatment performed by undergraduate dental students and to assess the outcome of the treatment if the remaining fragment was left or removed from the root canal.

METHODOLOGY

A retrospective analysis was performed by reviewing assessment forms (n = 3854) filled out for each root canal treatment over a 10-year period (1997-2006) at the University of Bergen, Norway. Based on the assessment forms, all instrument fractures and data concerning type and dimension of the fractured instruments were identified. Moreover, the affected tooth, root, root curvature and the vertical level of the fragment in the root canal were recorded. To assess the outcome of the root canal treatment, radiographs taken at follow-ups were evaluated by two individual examiners.

RESULTS

The overall incidence of instrument fracture during the period was 1.0% on a tooth level. Instrument fracture occurred significantly more often in molars and in teeth rated as difficult preoperatively. Of all instrument fractures, 39.5% were located in the mesio-buccal canals of molars, and 76.5% of the fragments were located apically. A significant high percentage of instruments of small apical diameter (sizes 006-015) fractured in relative straight root canals. The treatment was successful in 71.4% of the cases where the instrument fragment was removed, but only in 56.5% of the cases where the fragment remained in the root canal. Significantly more instruments were removed from teeth with a primary infection (P ≤ 0.05). The success rate for teeth with instrument fracture was 72.7% for vital teeth, 58.3% for primary infected teeth and 42.9% in retreatment cases.

CONCLUSIONS

Within the limits of the present study, the results indicate that the preoperative diagnosis is important for the final treatment outcome and that removal of the fragment is important in cases with primary infection.

HyFlex nickel-titanium rotary instruments after clinical use: metallurgical properties

AIM

To analyse the type and location of defects in HyFlex CM instruments after clinical use in a graduate endodontic programme and to examine the impact of clinical use on their metallurgical properties.

METHODOLOGY

A total of 468 HyFlex CM instruments discarded from a graduate endodontic programme were collected after use in three teeth. The incidence and type of instrument defects were analysed. The lateral surfaces of the defect instruments were examined by scanning electron microscopy. New and clinically used instruments were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Vickers hardness was measured with a 200-g load near the flutes for new and clinically used axially sectioned instruments. Data were analysed using one-way anova or Tukey's multiple comparison test.

RESULTS

Of the 468 HyFlex instruments collected, no fractures were observed and 16 (3.4%) revealed deformation. Of all the unwound instruments, size 20, .04 taper unwound the most often (n = 5) followed by size 25, .08 taper (n = 4). The trend of DSC plots of new instruments and clinically used (with and without defects) instruments groups were very similar. The DSC analyses showed that HyFlex instruments had an austenite transformation completion or austenite-finish (Af ) temperature exceeding 37 °C. The Af temperatures of HyFlex instruments (with or without defects) after multiple clinical use were much lower than in new instruments (P < 0.05). The enthalpy values for the transformation from martensitic to austenitic on deformed instruments were smaller than in the new instruments at the tip region (P < 0.05). XRD results showed that NiTi instruments had austenite and martensite structure on both new and used HyFlex instruments at room temperature. No significant difference in microhardness was detected amongst new and used instruments (with and without defects).

CONCLUSIONS

The risk of HyFlex instruments fracture in the canal is very low when instruments are discarded after three cases of clinical use. New HyFlex instruments were a mixture of martensite and austenite structure at body temperature. Multiple clinical use caused significant changes in the microstructural properties of HyFlex instruments. Smaller instruments should be considered as single-use.

Induction of osteogenic differentiation of adipose derived stem cells by microstructured nitinol actuator-mediated mechanical stress

The development of large tissue engineered bone remains a challenge in vitro, therefore the use of hybrid-implants might offer a bridge between tissue engineering and dense metal or ceramic implants. Especially the combination of the pseudoelastic implant material Nitinol (NiTi) with adipose derived stem cells (ASCs) opens new opportunities, as ASCs are able to differentiate osteogenically and therefore enhance osseointegration of implants. Due to limited knowledge about the effects of NiTi-structures manufactured by selective laser melting (SLM) on ASCs the study started with an evaluation of cytocompatibility followed by the investigation of the use of SLM-generated 3-dimensional NiTi-structures preseeded with ASCs as osteoimplant model. In this study we could demonstrate for the first time that osteogenic differentiation of ASCs can be induced by implant-mediated mechanical stimulation without support of osteogenic cell culture media. By use of an innovative implant design and synthesis via SLM-technique we achieved high rates of vital cells, proper osteogenic differentiation and mechanically loadable NiTi-scaffolds could be achieved.

Failure of ProTaper rotary Ni-Ti instruments used by undergraduate students

Objective: To evaluate the effect of number of uses, angle and radius of curvature and type of instrument on the fracture of ProTaper rotary instruments when used by undergraduate students. Study Design: Three hundred and seventy-six molars, with a total of 1114 root canals, extracted were instrumented by undergraduate students using ProTaper instruments according to the manufacturer´s recommendations. When fracture occurred, data were collected concerning the number of uses, type of instrument, level of fracture, angle and radius of curvature. ANOVA test were used to determine the influence of type of instrument in the incidence of instrument fracture. Logistic regression model was used to determine the influence of number of uses, angle and radius of curvature in the incidence of instrument fracture. Significance was set at p< 0.05. Results: A total of 37 Ni-Ti rotary instruments fractured during the treatment. Fracture occurred in 9.84% (37/376) of the teeth treated and 3.32% of the canals prepared with Ni-Ti rotary instruments (37/1114). A decrease in the radius of curvature of the canal significantly increased the likelihood of fracture (p=0.0001). Instrument fracture significantly increased as the number of uses increased (p=0.0037). No significant differences were found between the 6 types of ProTaper instruments (p=0.8). A reduction in the angle of curvature did not produce a significant decrease in the incidence of instrument separation (p=0.08). Conclusions: The results of this study imply that instrument fracture is linked to radius of curvature and number of uses.

Key words:Fracture, ProTaper ®, root canal preparation, undergraduate students.

Predicting in vivo failure of rotary nickel-titanium endodontic instruments under cyclic fatigue

The aim of this study was to examine the lifespan or number of cycles to failure of tapered rotary nickel-titanium (Ni-Ti) endodontic instruments. Simulated root canals with different curvatures were used to determine a relation between canal curvature and instrument lifespan. Using a novel mathematical model for the deformation of pseudoelastic Ni-Ti alloy, it was shown that maximum stress need not necessarily occur at the outer layer. On the basis of this observation, the Coffin-Manson relation was modified with parameters determined from this experiment. Results showed that the number of cycles to failure was influenced by the angle and radius of canal curvature and the size of instrument at the beginning of canal curvature. The resulting quantitative mathematical relation could be used to predict the lifespan of rotary Ni-Ti endodontic instruments under clinical conditions and thereby reduce the incidence of instrument failure in vivo.

Comparative evaluation of surface changes in four Ni-Ti instruments with successive uses - An SEM study

AIM

To evaluate the surface alterations seen in four kinds of Nickel-Titanium (Ni-Ti) instruments using a scanning electron microscope (SEM) for five successive uses in preparing root canals of extracted human molars and also to determine whether the design of the instrument influenced the appearance of defects on the instrument surface.

MATERIALS AND METHODS

Four different types of instruments namely; ProFile, ProTaper Rotary, ProTaper Hand and K3 Endo were used in 300 mesio-buccal canals. The instruments were examined under the SEM, after every use, to assess the progress of changes on their surfaces for a maximum of five uses.

STATISTICAL ANALYSIS USED

Chi-square test.

RESULTS

The most prevalent defects observed were pitting, followed by metal strips. Signs of discontinuity, microfractures and disruption of cutting edge were also evident. Number of defects increased with successive uses.

CONCLUSIONS

ProTaper Hand showed significantly more microfractures and metal strips than other instruments from third use onwards. ProTaper Rotary and K3 Endo also showed significant changes.

Instrument separation analysis of multi-used ProTaper Universal rotary system during root canal therapy

INTRODUCTION

The purpose of this study was to identify the influential factors responsible for clinical instrument separation of reused ProTaper Universal rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland).

METHODS

Six thousand one hundred fifty-four root canals in 2,654 teeth were prepared using ProTaper Universal files in endodontic clinics. Separation incidence was determined based on the number of treated teeth or canals. Data were collected including the size of fractured instrument, the length and location of a broken segment within the root canal, and the curvature of canal. The chi-square test and independent samples t test were used to determine the statistical significance.

RESULTS

The overall instrument separation incidences were 2.6% according to the number of teeth and 1.1% according to the canal number, respectively. Separation incidences according to the number of teeth or canals were significantly higher (P < .05) in molars than those in premolars or anterior teeth. Because of its largest diameter, F3 file presented the highest separation incidence according to the number of teeth (1.0%) or canals (0.4%); 47.5% instrument separation of mandibular molars and 61.5% instrument separation of maxillary molars happened in the mesiobuccal canals. Moreover, 91.4% fragments were located in the apical third of root canals, and 54.2% instrument separation occurred in severely curved canals. There was a significant difference (P < .05) in the mean fracture length between shaping (2.42 ± 0.73 mm) and finishing files (3.32 ± 0.73 mm).

CONCLUSIONS

Separation incidence according to the canal number is more reliable than that according to the number of teeth because of the variable canal number in different teeth. The tooth type, rotary file size, canal location, and anatomy were correlated with the instrument separation of reused ProTaper Universal files.

Geometric and dimensional characteristics of simulated curved canals prepared with proTaper instruments

Objective

This study identified which regions of ProTaper instruments work during curved root canal instrumentation.

Material and methods

Twelve ProTaper instruments of each type, S1, S2, F1, and F2, were assessed morphometrically by measuring tip angle, tip length, tip diameter, length of each pitch along the cutting blades, and instrument diameter at each millimeter from the tip. Curved canals in resin blocks were explored with manual stainless steel files and prepared with ProTaper instruments until the apical end following four distinct sequences of instrumentation: S1; S1 and S2; S1, S2, and F1; S1, S2, F1, and F2. Image analysis was employed for measuring canal diameters. The diameters of the canals and diameters of the instruments were compared. Data were analyzed by one-way ANOVA and Tukey’s test.

Results

No statistically significant difference was found between the canals and instrument diameters (p>0.05). The largest diameters in the end-point of the instrumented canals were obtained with F1 and F2 instruments and in the initial and middle thirds with S1 and S2 instruments.

Conclusions

All instruments worked at the tip and along their cutting blades, being susceptible to fail by torsion, fatigue, or the combination of these two mechanisms.

Defects in nickel-titanium instruments after clinical use. Part 5: single use from endodontic specialty practices

INTRODUCTION

Single 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.

METHODS

A 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.

RESULTS

There 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.

CONCLUSION

The 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.

Torsional behaviour of rotary NiTi ProTaper Universal instruments after multiple clinical use

AIM

To assess the influence of multiple clinical uses on the torsional behaviour of ProTaper Universal rotary NiTi instruments.

METHODOLOGY

Root canal treatments were performed on patients using the ProTaper Universal rotary system to prepare canals. Ten sets of instruments were used by an experienced endodontist, each set being used in five molar teeth. After clinical use, S1, S2, F1 and F2 instruments were analysed for damage by optical and scanning electron microscopy. The used sets, along with a control group of 10 sets of new instruments, were then torsion tested based on the ISO 3630-1 specification. Data obtained were subjected to a one-way analysis of variance (anova) with alpha = 0.05.

RESULTS

The use of the ProTaper Universal rotary instruments by an experienced endodontist allowed for the cleaning and shaping of the root canal system of five molar teeth without fracture. The maximum torque for instruments S2, F1 and F2, and the angular deflection at fracture for instruments S2 and F1 were significantly lower following clinical use. The largest decrease in maximum torque was 18.6% (P = 0.014) for S2 instruments. The same maximum percent decrease was found for angular deflection at fracture for F1 instruments (P = 0.009).

CONCLUSIONS

Torsional resistance and angular deflection of used instruments, as compared to that of new instruments, were reduced following clinical use.

A review of cyclic fatigue testing of nickel-titanium rotary instruments

INTRODUCTION

Fractured rotary nickel-titanium (NiTi) instruments have been classified into those that fail as a result of cyclic flexural fatigue or torsional failure or a combination of both. Clinically, NiTi rotary instruments are subjected to both torsional load and cyclic fatigue, and ongoing research aims to clarify the relative contributions of both factors to instrument separation.

METHODS

To date, there is no specification or international standard to test cyclic fatigue resistance of endodontic rotary instruments. As a consequence, several devices and methods have been used to investigate in vitro cyclic fatigue fracture resistance of NiTi rotary endodontic instruments. In nearly all studies reported in the endodontic literature, the rotating instrument was either confined in a glass or metal tube, in a grooved block-and-rod assembly, or in a sloped metal block.

RESULTS

There has been no mention of the "fit" of the instrument in the tube or groove. As the instrument is likely to be fitting loosely, the description of the radius of curvature in those studies is likely to be overstated (ie, the file was actually bent less severely than reported, adding a variability in the amount of flexural stress).

CONCLUSIONS

This review analyzed several devices that have been used in endodontic literature for cyclic fatigue testing and found that differences in the methodology affected the fatigue behavior of rotary instruments and, consequently, the outcome of these studies. An international standard for cyclic fatigue testing of NiTi rotary instruments is required to ensure uniformity of methodology and comparable results.