Life span of Neoendo Flex and ProTaper Next rotary files with reciprocating motion in single-rooted teeth

Abstract

Background:

Cleaning and shaping represent a vital step in the endodontic procedure. In routine endodontic therapy, the fracture of nickel–titanium (NiTi) instruments is a procedural problem creating a major obstacle to therapy.

Aim:

This study examines the life span of one Neoendo Flex and ProTaper Next (PTN) rotary file using reciprocating motion and compares the time required by both file systems for canal preparation.

Materials and Methods:

One hundred maxillary permanent central incisors were selected. In that, fifty teeth are utilized in a reciprocating motion (RM) with the PTN file (n = 25) and Neoendo Flex file (n = 25). To check fractured resistance and the overall root canal preparation time, fifty more teeth are employed in continuous motion (CM) with canals prepared using PTN (n = 25) and Neoendo Flex (n = 25). All canals are prepared following the sequence of respective files. Later, the fracture mechanism of the files was inspected using a scanning electron microscope.

Results:

In an RM motion, both PTN and Neoendo Flex files can be used in a minimum of 25 canals in single-rooted teeth. Statistical analysis using the Mann–Whitney U-test showed no significant difference in total time taken by PTN and Neoendo Flex in both motions.

Conclusion:

Within the limitation of this study, the RM was found to be better than CM with less incidence of instrument fracture.

INTRODUCTION

A successful endodontic outcome can be achieved only through meticulous root canal cleaning and contouring. It involves clearing the root canal space of pathogenic bacteria, pulp tissue, necrotized dentin, and its debris.[1] Rotary instruments made up of nickel–titanium (NiTi) were introduced in the field of endodontics and have greatly changed the way of preparation of root canals by reducing the problems associated with stainless steel instruments such as a ledge, perforation, and root canal transportation.[2,3] Because of their property of high flexibility and cutting efficiency.[4] In addition to it, canal preparation by rotary NiTi instruments in contrast to stainless steel hand files is easier and more rapid with minimal deviation from the original shape of the canal.[5,6] In routine therapy, fracture of endodontic instruments is a procedural problem creating a major hindrance to normal treatment. In recent years, endodontic instruments have undergone a series of changes and also changes in the kinematics of movement have been introduced to improve efficiency and decrease instrument fracture. Therefore, it has been suggested that using reciprocating motion (RM) rather than traditional rotation motion is preferable for preparing the canals with NiTi rotary instruments.[7-9]

Therefore, this study intended to examine the life span of the ProTaper Next (PTN) and Neoendo Flex file when it was used in reciprocating and full rotation motion. The efficiency of RM was also compared to full rotation in terms of the amount of time required for root canal preparation.

MATERIALS AND METHODS

This study uses 100 single-rooted extracted maxillary permanent central incisors to standardize the sample. To establish the existence of the mature root and the lack of root filling, calcification, other obstruction, or resorption, a radiographic examination of every tooth was performed. The teeth were cleaned of soft tissue and calculus and kept in a 0.9% physiological saline solution until usage. Later, the teeth were placed in a radio mount made of silicon-based impression material (3M ESPE Putty) to maintain a constant position.

Following the use of an Endo Access Bur to make the access cavities, a #10 K-file is inserted into the root canal to help reach the apical foramen. The root canal’s working length is calculated by taking 1 mm away from the apical foramen. Later, a #15 K-file was used to create a glide path.

After that, with the Nuro Dua Endomotor fifty teeth are employed in a RM (clockwise 150° and anticlockwise 30°) to prepare canals utilizing PTN (n = 25) and Neoendo Flex (n = 25) file system.

Continuous motion (CM) is performed on the remaining teeth while PTN (n = 25) and Neoendo Flex (n = 25) are sequentially employed to prepare the canals. Torque and rotational speed were used as recommended by the manufacturer.

Files are used sequentially in both RM and CM, i.e., X1, X2, and X3 for PTN and 17/04%, 20/04%, and 25/04% for Neoendo Flex.

All of the root canal procedures were carried out by only one operator. The broken files were inspected under the scanning electron microscope (SEM) (Carl ZEISS EVO) for revealing the fracture mechanism.

Overall preparatory period

PTN (n = 25) and Neoendo Flex (n = 25) were used to prepare the canals in both the RM group (n = 50) and the CM group (n = 50) following the sequences X1>X2>X3 and 17/04%, 20/04%, and 25/04%, respectively. Following the use of each file, 2 ml of 3.5% NaOCl irrigation of the canal was conducted with a 27-gauge side-vented needle, and RCT Prep (17% EDTA with carbamide peroxide) was used as a lubricant for the file. Normal saline is used as a last rinse to remove any remaining chemical irrigant.[10]

Leaving out the time needed to switch files and irrigate the canals, the total amount of time needed for root canal preparation was calculated when the workable length was attained by the master apical file. Statistics were used to analyze the outcomes.

RESULTS

In single-rooted maxillary central incisors, PTN and Neoendo Flex files can be used in more than 25 canals when used sequentially in a RM. However, in CM, ProTaper can be used in 23 canals and Neoendo Flex in 19 canals. The overall preparatory period for PTN and Neoendo Flex in RM was 54.27 s and 48.16 s, respectively. The Mann–Whitney U-test statistical analysis reveals no difference that is significant (P = 0.69). In CM, it was 1 min 22 s and 1 min 14 s by PTN and Neoendo Flex, respectively, which was statistically not significant on applying Mann–Whitney U-test (P = 0.33) [Table 1].

Table 1.

Overall preparatory period and number of usage of files

	Number of use	Average time taken for single canal preparation
RM
PTN	>25	54.27 s
Neoendo Flex	>25	48.16 s
CM
PTN	23	1 min 22 s
Neoendo Flex	19	1 min 14 s

PTN: ProTaper Next, RM: Reciprocating motion, CM: Continuous motion

Viewing a broken file longitudinally using SEM revealed that both files had suffered flexural fractures without any distortion [Figure 1], while the sectional view displayed both the cracks, fatigue striations, dimples, and abrasion marks typical of both flexural and torsional failure [Figure 2].

Figure 1.

Longitudinal view of fractured file: (a) ProTaper Next, (b) Neoendo Flex file

Figure 2.

Representative scanning electron picture of fractured file cross-sectional view of file revealing striation marks and microvoids: (a) ProTaper Next, (b) Neoendo Flex file

DISCUSSION

Manufacturers now do not advise more than one use of NiTi rotary instruments;[11] however, a look reported that certain units could be used in as many as five canals without affecting metallurgical properties.[12] Furthermore, when NiTi files are deformed or when the user turns into insecure about the state of the file, it is endorsed to discard them; nonetheless, research on the frequency of fractures in a specific type of NiTi file is very few, so the life span of a single master apical rotary file of the PTN and Neoendo Flex file systems was examined for the first time in this work.

The development of NiTi files to date can be described in several phases. The earliest instrument improvements are in the micromilled instruments constructed from standard NiTi wire. Manufacturers created features such as cross-sections, the design of tip, surface treatments, and taper along the length of the cutting blade in this initial phase to ameliorate the characteristics of the rotary instrument.[13,14] Numerous tests have demonstrated that compared to stainless steel files, NiTi instruments stand substantially more centered and exhibit little canal transportation.[15]

New kinematics were adopted in the second phase. For decades, stainless steel files had been employed in a RM to prepare root canals.

As a new version of the ProTaper Universal system, PTN files (Dentsply Sirona, 2013) have a rectangular cross-section, designed with variable taper and offset the mass of rotation, this PTN rotary file’s unique design reduces the screwing impact by reducing the binding of dentin. PTN files (Dentsply Sirona, 2013) are an updated version of the ProTaper Universal system. They include a rectangular cross section, variable taper, and offset the mass of rotation. Because of their innovative design, these PTN rotary files have less dentin binding, which reduces the chance for taper lock. These files are created with the use of M-wire NiTi alloy. To increase cyclic fatigue resistance and improve flexibility. These files were produced using M-wire NiTi alloy in order to increase cycle fatigue resistance and flexibility.[16,17]

Neoendo Flex files (Orikam Healthcare India Private Limited, 2013), are recently designed files with a triangular cross-section and gold thermal treatment, making them exceptionally flexible. In addition, according to the producers, the flutes do not open when the stress level is met, increasing cyclic fatigue resistance.[18]

The Taper of Neoendo Flex files used in our study were 4% and PTN files have varied taper designs on the entire length of the file.

Yared in 2008 was the first to study a RM that used the ProTaper F2 instrument. The study demonstrated a significant decrease in the number of instruments required to clean and shape the canal, as well as a reduction in potential contamination and operator concern related to instrument failure.[19]

You et al. in 2010 examined the durability of rotary files at the time of preparation of You et al. in 2010 examined the durability of rotary files at the time of preparation of curved root canals extracted molars root canal with curvature, using a series of ProTaper SX, S1, S2, F1, and F2 files in continuous rotation, and a ProTaper F2 instrument in a RM. One F2 file was found to have an average life span of 10 canals and the longest one had 21 canals for the RM.[20]

In RM, the change in direction of rotation alternatively reduces the number of cycles of the instrument and thus reduces the cyclic fatigue on the instrument[21,22] and it also reduces the binding of an instrument into the dentinal wall of the root canal, therefore reducing the torsional stress compared with that assessed when instruments are used in a conventional rotational motion.[23] Thus, it is clear why RM outperforms continuous rotation in terms of performance.

When using NiTi rotary instruments, a fracture is a major drawback.[24] The clinical concern is that they undergo unanticipated fractures without any alert fractures can occur without any apparent flaws from earlier permanent deformation. Therefore, for the assessment of utilized NiTi instruments, a visible examination is not reliable. Endodontic rotary instrument fractures may happen in one of two situations: flexural fatigue and torsion fracture.[25,26] A torsional fracture happens when the instrument’s tip or any other part is engaged in a canal while the shaft is still rotating. Flexural fatigue develops as a result of constant compression and strain in the curved canal.

In the therapeutic setting, the files are subjected to cyclic fatigue in addition to torsional stress in the root canal, and these two forces interact with one another.[27]

Consequently, when the fractured file’s cross-section is analyzed using SEM, the characteristics of both failures can be observed simultaneously. In the present study, both characteristics of ductile fracture, i.e., dimples, and characteristics of brittle fracture, i.e., cracks, and fatigue striations, are observed. RM minimizes torsional stress by avoiding the file’s binding as described in earlier studies and corroborated by our work. As a result, expectations are raised for the prolonged use of the file without a break.

CONCLUSION

Within the constraints of this research, it was discovered that RM was superior to CM and had a lower incidence of instrument fracture. In addition, there was no discernible difference between the Neoendo Flex file system and PTN in terms of how long it took to prepare the canals. To verify the results, however, additional research needs to be conducted with a bigger sample size.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.