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A Novel Root Canal Preparation Technique Hybridizing Heat- treated Nickel-Titanium Rotary Instruments

Abstract

Aim: This study aimed to assess the potential of the hybrid heat treatment (HHT) technique for shaping severely curved canals.

Background: This innovative HHT technique combines the use of both Ni-Ti austenitic and martensitic Ni-Ti files, with a simplified sequence, to properly utilize the different files’ properties.

Case description: The operative technique started with canal scouting and determination of working length using a size 10 SS K-file. Then, a specific sequence was applied using the F1 20.06v Ni-Ti austenitic file (EdgeTaper) for the preparation of the coronal and middle parts of the canal. This step was followed by S2 20.04 and F120.06v martensitic Ni-Ti files (EdgeTaper Platinum) to enlarge the canal until the apex reached. No intracanal breakage of any instruments or deformation of flutes was recorded.

Conclusion: The present study describes a new HHT technique aiming at simplifying procedures and taking most of the different characteristics of the different heattreatment; the clinical cases seem to show its potentialities in terms of safety, speediness, effectiveness, and preservation of original anatomy.

Clinical significance: The cases show the advantages of the newly proposed technique over a traditional approach to properly shape complex anatomies with only a few Ni-Ti rotary instruments number.

Keywords: Endodontics, Hybrid heat treatment, Ni-Ti rotary instruments, Root canal treatment.

World Journal of Dentistry (2021): 10.5005/jp-journals-10015-1830

 

Click on link for full case: Hybrid Tech Case Study.

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Articles X7

The Relevance of Operative Torque and Torsional Resistance of Nickel-titanium Rotary Instruments: A Preliminary Clinical Investigation

Gianluca Gambarini, Gabriele Miccoli, Maurilio D’Angelo, Marco Seracchiani, Federico Valenti Obino, Rodolfo Reda, Luca Testarelli

Department of Oral and Maxillo-Facial Sciences, “Sapienza” University of Rome, Rome, Italy

Introduction

The aim of the present study is to evaluate the torsional resistance and the operative torque of two different files and to introduce the concept of “torque range”, that indicates the difference between torque at failure and operative torque.

Materials and Methods

20 ProTaper Next® (PTN) X1 and 20 EdgeFile® X7 17.04 were randomly divided into two equal groups (n = 10) and were subjected to the following two tests: operative torque recorded during root canal shaping of a single-rooted mandibular premolar and a torsional test performed at 300 rpm while the apical 3 mm of each file were firmly secured. The torque range was calculated from the difference between “Operative torque” and “torque at fracture.” A statistical t-test was performed to determinate the difference. Statistical significance was set at P < 0.05.

Results

EdgeFile X7 instruments reached the working length significantly faster and with less torque generated (P < 0.05) compared to PTN. In torsional static resistance (torque at failure), the two files demonstrated no significant different values (P > 0.05). The range between the mean values of maximum torque at failure and operative torque, “torque range,” was twice bigger for EdgeFile X7 instruments.

Conclusions

The EdgeFile X7 has a wider “torque range” when compared to PTN X1. This new concept could be a relevant innovation to match in vivo and in vitro studies and to obtain a more clinically relevant result.

 

Read full article here: The relevance of operative torque and torsional resistance of nickel-titanium rotary instruments: A preliminary clinical investigation

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Influence of Different Heat Treatments on Torsional and Cyclic Fatigue Resistance of Nickel-Titanium Rotary Files: A Comparative Study

Gianluca Gambarini, Andrea Cicconetti, Dario Di Nardo , Gabriele Miccoli *, Alessio Zanza, Luca Testarelli and Marco Seracchiani

 

Abstract:

Protaper Universal (PTU), Protaper Gold (PTG) (Maillefer, Ballaigues, CH), EdgeTaper (ET), and EdgeTaper Platinum (ETP) (Albuquerque, NM, USA) were tested for both torsional and flexural resistance. The aim of the present study was to evaluate the influence of proprietary heat treatment on the metallurgical properties of the aforementioned instruments. Four groups of 30 different instruments (size 20.07) were tested, then divided into two subgroups of 15 instruments—one for the cyclic fatigue test in a curved canal (90◦—2 mm radius) at 300 rpm and 2.5 Ncm. The time to fracture (TtF) and fragment length (FL) were recorded. The other subgroup was subjected to the torsional test (300 rpm, 5.5 Ncm). The torque to fracture and TtF were recorded. All the instruments underwent a SEM analysis. The heat-treated instruments showed a significantly higher fatigue resistance than the non-heat-treated instruments (p < 0.05). No significant differences were found in the torsional resistance between the ET and PTU, and the ETP and PTG. However, when comparing all the groups, the heat-treated instruments showed less torsional resistance. The improvement from heat treatment was mainly found in the cyclic fatigue resistance.

Introduction:

The intracanal fracture of nickel–titanium (NiTi) rotary files is still one of the main concerns during root canal therapy. It has been demonstrated by many authors that rotary NiTi files essentially fail for two main reasons: flexural (cyclic) fatigue and torsional failure [1,2]. The cyclic fatigue failure of the file occurs because of the repeated compressive and tensile stresses that accumulate at the file’s point of maximum-stress, which is located at the maximum curvature point inside the root canal’s anatomy [3]. Torsional failure occurs when the tip (or some part of the file) binds (or is blocked inside) the root canal, while the motor continues to rotate until the torsional limits are overcome and a fracture occurs [4]. The mechanical resistance of NiTi rotary files has been tested in two different ways: cyclic fatigue tests and the torsional test. When investigating cyclic fatigue, instruments are usually rotated inside an artificial curved canal until a fracture occurs at the recommended rotation speed. When investigating the torsional resistance, based on the ADA testing recommendations for stainless steel manual files, the tip is usually locked at 2 mm and its rotation speed is 2 rpm. Unfortunately, there is no ADA standard that describes how to test nickel–titanium rotary files; therefore, studies and their results may differ significantly due to the different testing devices and different methodologies [5–7]. Over the past several years, improvements in design, alloys and manufacturing processes have been proposed to increase the mechanical resistance of NiTi rotary files. Several proprietary heat treatment applications have been developed. Studies have shown that thermal treatments (for files with the same geometry and design) enhance the cyclic fatigue lifespan while, at the same time, reducing the torsional resistance of a file [8–10]. Some studies have also compared heat-treated files and non-heat-treated files with different cross-sectional designs in cyclic fatigue tests, which demonstrate that heat treatment may not be the most influential parameter for flexural resistance [11]. Therefore, many other factors can influence mechanical resistance. Data have shown that different cross-sectional designs, tip and taper dimensions, pitch lengths, and operative motions could affect the resistance to both the flexural and torsional stresses [12–14]. Additional mass increases the torsional resistance and decreases the fatigue resistance [15]. However, very few studies have compared instruments of the same design (and different heat treatments) for both torsional and fatigue resistance [16,17]. Therefore, in the present study, four commercial instruments, with a similar design and tip and taper dimensions, were tested and compared, in order to assess if and how different heat treatments may affect both the torsional and flexural resistance.

Conclusions:

In conclusion, for both manufacturers, heat treatment revealed a significant impact on increasing the resistance to cyclic fatigue. In contrast, the torsional resistance was not improved by the heat treatments. Moreover, torsional failure may happen rapidly if the files become taper locked, since the recorded torque values at the point of failure were significantly lower than the operative torque values recommended by the manufacturers.

 

Read full article here: Influence of Different Heat Treatments on Torsional and Cyclic Fatigue Resistance of Nickel–Titanium Rotary Files: A Comparative Study

 

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Assessment of Real-Time Operative Torque during Nickel–Titanium Instrumentation with Different Lubricants

Alessandro Mazzoni, Andrea Pacifici , Alessio Zanza, Andrea Del Giudice, Rodolfo Reda, Luca Testarelli * , Gianluca Gambarini and Luciano Pacifici

Received: 31 July 2020; Accepted: 3 September 2020; Published: 7 September 2020

Featured Application: Evaluate the torque values by nickel–titanium rotary instruments during intracanal instrumentation.

 

Abstract:

The aim of the present study is twofold: to assess ex vivo the role of different lubricants on real-time torque generated during intracanal instrumentation and to check whether two different kinds of torque parameters, operative torque (OT) and average peak torque (APT), could produce similar results. Forty extracted single-rooted teeth were selected for the present study and divided into four equal groups (n = 10): Group A, NaCl 0.2%; Group B, NaOCl 5%; Group C, ethylenediaminetetraacetate (EDTA), and Group D, EDTA and hydrogen peroxide. Afterwards, Edge Taper F2 (Edge Endo, Albuquerque, New Mexico) were rotated clockwise at 300 rpm with 3 Ncm maximum torque by an endodontic torque recording motor. In each sample, mean OT and mean APT were recorded and statistically analyzed with one-way ANOVA and a post hoc Bonferroni between groups (p < 0.05). EDTA (12.11 ± 4.45 Ncm) showed statistically significant (p < 0.05) lower values compared with the other tested irrigant for both parameters. Overall, the two different parameters were both able to differentiate between the influence of lubricants on torsional loads. Keywords: endodontics; nickel–titanium; torque; root-canal irrigants.

1. Introduction

Nickel–titanium rotary (NTR) instruments gained a primary role in root-canal treatment (RCT). Despite that, NTR instrument failure is approximately 1% of all RCTs [1,2]. Sattapan et al. (2000) reported that torsional stresses are the major responsible of the failure of these files in 55% of the examinedcases, while flexural stresses cause 45% of the failure [3]. This ratio could even be changed in recent years, since manufacturers have produced more flexible instruments thanks to the introduction of new heat treatment processes[4–6].

In the literature,many studies evaluated the torsional resistance of an NTR instrument, locking it 3 mm from the tip, whilst the motor rotates at 2 rpm until fracture occurs [7–9]. Despite being easier to perform, static tests do not reflect an instrument’s clinical performance during RCTs. Recently developed software and manufacturing allowed the realization of devices able to evaluate and record real-time torque variation. For this reason, thanks to these new devices, previous published studies managed to introduce the idea of an “operative torque” [10]. The “operative torque” (OT) is defined as the amount of torque needed by the instrument to reach the apex. Nowadays, it is obtained by measuring the measuring the torque generated by the instrument each 0.1 sand calculating the mean value. Therefore, it can be defined as the mean operative torque (MOT). Thanks to this parameter, it is now possible to evaluate the efficiency of an NTR instrument during RCT. However, despite the importance of introducing a parameter that allows the measurement of the stresses produced during root canal   shaping, operative torque relevance and the methods of calculation are still controversial. It is indeed influenced not only by the time need to perform the RCT but also by the technique used by the clinician. Despite the primary role of NTR instruments in shaping the root canal, the aim of endodontic treatment is to allow irrigant penetration through the endodontic space, not only focus in gon the main canal [11]. Moreover, the seirrigants and lubricants are used to emulsify and clean the debris produced by the cutting action of the endodontic instruments, this way facilitating the instruments’ progression [12]. 

Irrigants are produced in two different forms: aqueous and paste-type lubricants. The aqueous irrigants, such as sodium hypochlorite (NaOCl) and ethylenediaminetetraacetate (EDTA) are primarily used as surfactants and to suspend debris [13]. NaOCl is the most used irrigant in endodontics considering its superiority in removing the smearlayer. 

Chelating agents, such as EDTA, create stable calcium complexes with smear layers and calcific deposits along the dentinal walls [14]. The seagents act on calcified tissue by subtracting sodium ions, which in combination with dentine, give a soluble salt with calcium ions. Paste-type substances, such as combinations of EDTA and carbamide peroxide or EDTA and ureaperoxide, are marketed by rotary manufacturers and first lyimprove hard tissue debridement [15]. The hard tissue debridement allows a lower blade engagement on the dentinal walls and consequently a lower torque generation by the instrument during intracanal instrumentation. Furthermore, the chelating and lubricating actions of EDTA ensure the debris removal from the rotating instrument. Moreover, chemical additives, such as peroxides, could soften the dentinal walls to facilitate instrumentation and instrument progression towards the apex[12].

In the current literature, many studies evaluated the different characteristics and molecular pattern of different types of lubricants [16–21]. Most of these studies focused their attentions on the various effects in reducing and eliminating smear layer and debris during RCTs. In the last fifteen years, a small number of studies have tried to investigate the role of lubricants on torque generated during instrumentation. However, these studies tested the instruments in a simulated root-canal system and focused on maximum torque value reached by the instrument during the instrumentation [22,23]. Moreover, to date, no published studies evaluated the efficacy of different irrigants on reducing operative torque. Therefore, the aim of the present study is two fold: to evaluate the role of different lubricants on real-time torque generated during intracanal ex vivo instrumentation and to propose a new methodology to assess real-time operative torque.

Read full article here: Assessment of Real-Time Operative Torque during Nickel–Titanium Instrumentation with Different Lubricants 

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In Vivo Evaluation of Operative Torque Generated by Two Nickel-Titanium Rotary Instruments during Root Canal Preparation

Objectives This in vivo study evaluated the operative torque and preparation time of ProTaper NEXT (Dentsply Maillefer; Ballaigues, Switzerland) and EdgeFile X7 (EdgeEn-do; Albuquerque, New Mexico, United States) rotary systems during root canal prepa-ration of maxillary premolars. Materials and Methods Ten double-rooted maxillary premolars with independent canals were selected. Each canal in each tooth was prepared with one of the rotary systems (n = 10), ProTaper NEXT or EdgeFile X7. The instruments were rotated at 300 rpm with maximum torque set at 2 N.cm using an electric motor (KaVo; Biberach, Germany) that automatically recorded torque values at every 1/10th of a second (ds). Statistical Analysis Operative torque (N.cm) and preparation time (s) of the first shaping instrument (size 17/.04) of both rotary systems were recorded and statistical-ly compared using the Mann– Whiney U test with a significance level set at 5%. Results No instrument exhibited flute deformation or underwent intracanal fail-ure. No differences were found between the instruments regarding the maximum (peak) torque values (p > 0.05). EdgeFile X7 17/.04 required significantly less prepa-ration time (3.75 seconds interquartile range [IQR]: 3.2–9.0) than ProTaper NEXT X1 (15.45 seconds IQR: 8.35–21.1) (p < 0.05). The median operative torque values of Pro-Taper NEXT X1 (0.26 N.cm; IQR: 0.18–0.49) were significantly higher compared with EdgeFile X7 17/.04 (0.09 N.cm; IQR: 0.05–0.17) (p < 0.05). Conclusions Although no difference was found between the median peak torque values of ProTaper NEXT X1 and EdgeFile X7 17/.04 instruments, the operative torque and instrumentation time results were impacted by their different designs and alloys during clinical preparation of root canals. Click Here for Full Article: In Vivo Evaluation of Operative Torque Generated by Two Nickel-Titanium Rotary Instruments during Root Canal Preparation
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Articles X7

Torsional resistance of two nickel-titanium rotary instruments: A comparative study

This study explores how heat treatment less significantly influences (increasing or decreasing) torsional resistance when compared to the high increase in flexibility and fatigue resistance reported in many published articles. Moreover, torsional fracture occurs extremely rapidly when an instrument’s tip becomes blocked.

Introduction

The main mechanisms of nickel-titanium (NiTi) endodontic instrument fracture have been revealed as two modes of failure, one being torsional failure and the other cyclic fatigue. The former contributes to a significant proportion of failures.1 Cyclic fatigue fracture is caused by repetitive compressive and tensile stresses on the outermost fibres of a file rotating in a curved root canal, and torsional failure occurs when the tip of the instrument binds to the canal wall, even in a straight root canal.1

Cyclic fatigue resistance of NiTi instruments has been assessed extensively.2 In contrast, there is less information available on torsional fracture resistance tests.3 The main method of testing for static rotational fracture is the comparison of the torsional resistance of the instruments as described by ISO 3630-1. According to this specification, the 3 mm file tip must be fixed with brass and a rotational speed of 2 rpm applied to create a continuous torsional load until fracture occurs.3

Torsional load can be limited during intra-canal rotary instrumentation by the torque-controlled endodonticmotor: torque settings can be selected to prevent excessive torsional load on the instruments. It has been shown that the correct preset torque value for each instrument is very difficult to determine.4 If it is too high, safety becomes dependent on the clinician’s skill in avoiding over-engagement and/or blockage of the file. If it is too low, the rotary instrument will be loaded by repeated locking and release through use of the torque-controlled motor or auto-reverse function. However, in narrow canals, where instruments are subject to higher torsional stresses than in wider canals, the chance of experiencing these repetitive torsional loads is increased.

To this point, torque value at failure according to the ISO test has not been commonly used to determine torque settings in torque-controlled motors. In most cases, values are higher than torque at failure. As a consequence, the concept that the use of a preset torque value that is considered safe (i.e. capable of preventing shear fracture of the instrument) is not completely accurate. Therefore, NiTi rotary instruments should ideally exhibit a good resistance to torsion in all cases and in curved canals should also be flexible and resistant to cyclic fatigue.

Many factors can affect resistance to torsion, including design, dimensions, manufacturing process and motion.5 In the present study, two NiTi rotary instruments, similar in dimensions and design, were tested to compare torque at failure. The null hypothesis was that any differences found would be related to different manufacturing processes.

Methodology

The following instruments from two different systems were tested and compared: ProTaper Next (Dentsply Maillefer) and EdgeFile X7 (EdgeEndo). For each brand, ten 17/0.04 instruments were subjected to a repetitive torsional test. The test was performed using a torque-controlled endodontic motor (MASTERsurg, KaVo). The motor allowed for precise recording of torque values during the instruments’ use. The accuracy and reliability of the device had been validated in a previous study.6 To perform the test, the apical 3 mm of each file was firmly secured, embedded in a resin block produced with a mixed autopolymerising resin (DuraLay, Reliance Dental Manufacturing). Each file was then rotated clockwise at a speed of 300 rpm until fracture occurred. The torque limit was set at 5.5 N cm, to ensure recording measurements ranging from 0.1 to 5.5 N cm. The torque values at failure were recorded by the integrated software of the motor and analysed using spreadsheet software. The data was analysed using one-way analysis of variance and a Tukey test with a significance level of α = 5%.

Results

Table 1 shows the results from the present study. The ProTaper Next files demonstrated no significantly different levels of resistance in terms of maximum torque at failure compared with the EdgeFile X7 instruments (p < 0.05). Similarly, no statistically significant differences were found between the two instruments in terms of time to failure (p < 0.05).

Table 1: torque at failure  (N/cm) Maximum torque (SD ) Time to failure ( seconds)
Edge ENDO X7  0, 57 (± 0,1) 0,42 (± 3,5 )
Protaper Next 0,51 (± 0,1) 0,39 (± 2,9)

Discussion

The ISO torsional resistance static test was developed more than 50 years ago to test manual stainless-steel instruments and is probably not ideal for testing rotary instruments that rotate at speeds much higher than 2 rpm or for the specific motors with torque control and auto-reverse mode.7 Therefore, in the present study, torsional resistance was assessed by using a different speed: the clinical speed (300 rpm).

The tested instruments were similar in dimension and design but had been produced through different manufacturing processes (alloys and heat treatments). According to the manufacturer’s website, EdgeFile X7 files exhibit a higher flexibility and a greater resistance to cyclic fatigue than competitors’ instruments do. In stainless-steel instruments, flexibility and torsional resistance are usually inversely proportional, which is mainly due to the mass and/or dimensions of the instruments. The greater the mass, the more rigid and resistant to static torsion the instrument is.8 In the present case, mass and dimensions were very similar, and torsional resistance was similar, showing no statistically significant difference between the two instruments. The null hypothesis was therefore rejected.

Hence, the present study showed that heat treatment does not significantly influence torsional resistance in contrast to the high increase in flexibility and fatigue resistance derived from heat treatment as reported in many published articles.9, 10

References:

  1. Sattapan B, Nervo GJ, Palamara JE, Messer HH. Defects in rotary nickel-titanium files after clinical use. J Endod. 2000 Mar;26:161–5.
  2. Plotino G, Grande NM, Cordaro M, Testarelli L, Gambarini G. A review of cyclic fatigue testing of nickel-titanium rotary instruments. J Endod. 2009 Nov;35(11):1469–76.
  3. Pedullà E, Grande NM, Plotino G, Gambarini G, Rapisarda E. Influence of continuous or reciprocating motion on cyclic fatigue resistance of 4 different nickel-titanium rotary instruments. J Endod. 2013 Feb;39(2):258–61.
  4. Gambarini G. Advantages and disadvantages of new torque-controlled endodontic motors and low-torque NiTi rotary instrumentation. Aust Endod J. 2001 Dec;27(3):99–104.
  5. Xu X, Eng M, Zheng Y, Eng D. Comparative study of torsional and bending properties for six models of nickel-titanium root canal instruments with different cross-sections. J Endod. 2006 Apr;32(4):372–5.
  6. Gambarini G, Seracchiani M, Piasecki L, Valenti Obino F, Galli M, Di Nardo D, Testarelli L. Measurement of torque generated during intracanal instrumentation in vivo. Int Endod J. 2019 May;52(5):737–45.
  7. Pedullà E, Lo Savio F, La Rosa GRM, Miccoli G, Bruno E, Rapisarda S, Chang SW,Rapisarda E, La Rosa G, Gambarini G, Testarelli L. Cyclic fatigue resistance,torsional resistance, and metallurgical characteristics of M3 Rotary and M3 ProGold NiTi files. Restor Dent Endod. 2018 Apr 23;43(2)
  8. Gambarini G, Testarelli L, Galli M, Tucci E, De Luca M. The effect of a new finishing process on the torsional resistance of twisted nickel-titanium rotary instruments. Minerva Stomatol. 2010 Jul-Aug;59(7-8):401-6.
  9. Braga LC, Faria Silva AC, Buono VT, de Azevedo Bahia MG. Impact of heat treatments on the fatigue resistance of different rotary nickel-titanium instruments. J Endod. 2014;40(9):1494–7
  10. Plotino G, Testarelli L, Al-Sudani D, Pongione G, Grande NM, Gambarini G. Fatigue resistance of rotary instruments manufactured using different nickel-titanium alloys: a comparative study. 2014;102(1):31–5

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