Comparative evaluation of apically extruded debris using three different thermomechanically heat treated file systems with two different motions: An in vitro study.

Introduction and Aim: Postoperative inflammation and endodontic failure occur due to apical extrusion of debris. The purpose of this in vitro study was to assess the amount of apically extruded debris during the root canal preparation using rotary and reciprocating nickel-titanium instrumentation systems. Materials and
Methods: The mesiobuccal canals of seventy five mature, human mandibular molars were randomly divided into three groups (n = 25 teeth/group). Each group was instrumented using one of the three different instrumentation systems: Hyflex EDM (HEDM) rotary file, Flexicon X7 rotary, and Flexicon X1 reciprocating files. The canals were irrigated using distilled water. The debris extruded apically was collected in preweighed Eppendorf tubes and assessed with an electronic balance and compared. Statistical Analysis: Data were statistically analyzed by one-way analysis of variance and the intergroup comparison with single factor ANOVA.
Results: The Flexicon X1 reciprocating system showed the maximum amount of apical extrusion of debris among all the groups. The least amount of debris was observed in Flexicon X7 rotary instrument (P > 0.05).
Conclusion: Flexicon X7 rotary extruded significantly lesser amount of debris than Flexicon X1 reciprocating and HEDM rotary file systems. Copyright:

INTRODUCTION

The success of endodontics is mainly based on thorough debridement, disinfection, and 3-D obturation. The main aim of cleaning and shaping is an enlargement of the canals without procedural errors.[1] Although various methodologies have been introduced, one inherent problem related to all root canal shaping and cleaning procedures is the extrusion of intracanal debris and irrigants into the periradicular tissues. The studies so far have proven that none of the various techniques and instruments can clean and shape the root canal system without producing some apically extruded debris (AED).[2]

Each system has its own advantages as well as disadvantages. For more than a decade, different rotary systems are in use, which may vary in their material property, cross-section, taper, symmetry, etc., The advent of single-file systems has exceedingly simplified the multistep rotary instrumentation into a single-step procedure. They have benefits such as lower costs, reduced shaping time, enabling the clinician to spend more time with more advanced irrigation techniques on cleaning the canal.

Hyflex EDM (HEDM) (Coltene-Whaledent, Switzerland) is single rotary file system produced by innovative manufacturing process called “Electrical Discharge Machining” using a controlled memory Niti wire[3] which has advantages such as high precision, creation of various designs without tool constraints, and limited manufacturing stress to the file surface. This method also produces a rough surface, which can enhance the cutting abilities of the file. This entirely unique combination of flexibility and fracture resistance makes it possible to reduce the number of files required for cleaning and shaping during root canal treatment without having to compromise preservation of the root canal anatomy. They have a three different cross-sectional design with 3 cutting edges. The rectangular cross section at the tip provides more “core material,” which results in high resistance to breakage of these files. Then the cross section becomes trapezoidal in the middle of the file and finally near the handle, the cross section changes to triangle which keeps the file more flexible there. It can be labeled as a unique combination of flexibility and strength. Unlike other instruments, distorted Hyflex instruments are able to recuperate their original shape after a sterilization procedure.

Flexicon (Edgeendo, Canada) files are made of an annealed heat treated to make it extremely flexible and resistant to torsional strain. Flexicon X1 reciprocating file is available in sizes 20, 25, 40. Flexicon X7 rotary file is available in 17, 20, 25, and taper 4% and 6%.[4] According to the manufacturer, Flexicon Fire Wire Ni–Ti yields better performance, enhancing its durability to provide incredible flexibility. It is also a modified version of the original WAVE ONE system. These files are produced with nickeltitanium Mwire alloy that goes through innovative heat treatment. This thermal process modifies the molecular structure to improve resistance to cyclic fatigue and increases flexibility. These systems use preprogrammed reciprocation motions that are specific to their file designs.

Each of these rotary and reciprocating file systems is known to have its unique design features, variable taper, and is based on different technology. Differences may also exist between them concerning AED. No previous studies have compared these three different thermo mechanically heat treated file systems; thus, the aim of the present study was to compare the amounts of AED using these three new different heat-treated Niti file systems with different file design features and motion kinematics.

MATERIALS AND METHODS

The research protocol of this experimental study was approved by the Institution's Ethics Committee Board. Seventy five freshly extracted mandibular molar teeth were selected. Teeth with complete root formation and straight root canals with <10° curvature were included in the study. The degree of curvature was calculated using the methodology described by Schneider method.[5] Teeth with internal resorption, root canal calcification, and curved root canals were excluded from the study.

The debris and soft-tissue remnants were cleaned from external root surface and then stored in distilled water. To maintain similar tooth lengths, all teeth were measured with vernier caliper and standardized as 16 ± 2 mm and the crowns were sectioned with a high speed bur under copious water spray until equal lengths were obtained. Access cavity preparation was done in each tooth and all external tooth surfaces were covered with 2 layers of nail polish except for 1 mm around the apical foramen. A #15 K-file (Mani, Tochigi, Japan) was used to determine the WL until it was visible at apical foramen. The WL was reestablished by subtracting 1 mm from this measurement. Teeth with initial apical diameter more than K-file size #15 were excluded from the study.

The debris collection apparatus was made according to the design described by Myers and Montgomery.[6] Eppendorf tubes were taken and weighed by electronic microbalance with 10 − 5 sensitivity (Single Pan, Mettler Toledo, JP105DUG/A, India). Each individual tooth was held in a preweighed Eppendorf tube which was fixed inside a glass vial through rubber plug. It was seen that no possible contact was made between the tube and the glass vial. The tube was vented with a 23 gauge needle to equalize the pressure inside and outside [Figure 1a] subsequently, the vial was covered with aluminum foil for isolation and blinding to avoid bias [Figure 1b].

Figure 1

(a) Debris collection apparatus (b) glass vials were wrapped with aluminum foil to avoid bias (c) Eppendorf tube with dried debris (d) readings of Eppendorf tubes with dried debris with electronic analytical balance of sensitivity 10 − 5 g

All the samples in the respective groups were prepared according to the manufacturer's instructions which were set into permanent rotation with a 6:1 reduction using X-SMART Plus endo motor (Dentsply Maillefer) [Table 1]. Flexicon X1 was used in a reciprocating working motion generated by the motor. Each instrument was used in a short in and out motion for a maximum of four times per instrument.

Table 1

File sequence

Group	Mode of preparation	Sequence of instrumentation	Torque (NCM)/RPM
Group - A (Hyflex EDM)	Crown down	0.12/#25 (orifice shaper) → 0.05/#10 (Glidepath file/working length) → 0.06/#25 one file (apical finishing till working length)	2.5/500
Group - B (flexicon X7)	Crown down	X7: 0.04/#17 (till working length) → 0.06/#17 (till working length) →0.04/#20 (till working length) →0.06/#20 (till working length) →0.04/#25 (apical finishing till working length) → 0.06/#25 (apical finishing till working length)	2.5/350
Group - C (flexicon X1)	Crown down	X1: 0.04/#17 (till working length) → 0.06/#17 (till working length) →0.06/#20 (till working length) → 0.06/#25 (apical finishing till working length)	2.5/350

EDM: Electric Discharge Machine, NCM: Newton-metre, RPM: Revolutions per minute

Groups

All the samples were randomly assigned to three groups containing (n = 25) teeth each, based on the file systems used for root canal preparation as mentioned below.

Group A – HEDM

Group B – Flexicon X7

Group C – Flexicon X1.

A total volume of 5 mL of distilled water was used in each root canal for irrigation. Irrigation was performed with an in-and-out motion of the syringe using a side-vented 30-gauge needle (Cerkamed Endo-Top, Poland) placed up to 3 mm of the working length. After completion of instrumentation, stopper was removed and AED attached to root tip was washed into Eppendorf tube with 1 mL of distilled water.

After canal preparation, the Eppendorf tube was removed from the glass vial. All the Eppendorf tubes were then placed in a hot air oven (BTI, India) at 140°C for 5 h to allow the evaporation of moisture before weighing the dry debris [Figure 1c]. For each Eppendorf tube, three consecutive measurements were taken and the mean measurement was considered to be its weight. The weight of extruded debris was calculated by subtracting pre experiment weight of the tube from the weight of tube with dried debris [Figure 1d]. The mean of the dry weight were statistically analyzed using Statistical Package for Social Sciences (SPSS) (version 22, Company IBM SPSS Statistics, Delhi, India) and the intergroup comparison between the groups were found using single factor ANOVA test and the P value was set at 0.05.

RESULTS

Results of ANOVA test indicated no statistical significant difference among the three groups (P > 0.05). As depicted in Graph 1 Flexicon X7 file system showed the least amount of debris extrusion. The highest amount of debris extrusion was displayed by Flexicon X1 followed by HEDM. The mean values and standard deviations for all groups are listed in Table 2 and intergroup comparison listed in Table 3.

Table 2

The mean values and standard deviation of apically extruded debris between three groups

Group	Apical extrusion of debris (mg)
	n	Minimum extrusion	Maximum extrusion	Mean	SD
Group - A (Hyflex EDM)	25	−0.00027	0.03054	0.00741	0.00000
Group - B (flexicon X7)	25	0.00215	0.02647	0.00670	0.00001
Group - C (flexicon X1)	25	0.00019	0.02647	0.00775	0.00000

SD: Standard deviation, EDM: Electric Discharge Machine

Table 3

Inter-group comparison of all groups with rotary and reciprocating systems by using one way ANOVA test with a level of significance set at P<0.05

Comparison between groups	P
Group - A (Hyflex EDM)
Group - B (flexicon X7)	0.606653
Group - C (flexicon X1)	0.88583
Group - B (flexicon X7)
Group - C (flexicon X1)	0.720746

EDM: Electric Discharge Machine

DISCUSSION

Apical extrusion of infected debris may potentially disrupt the balance between microbial aggression and the host's protection, resulting in episodes of periapical inflammation and flare-ups.

Various factors that affect apical extrusion are patency, apical diameter, canal curvature, working length, instrument design, technique of instrumentation, irrigation needle type, needle insertion depth, and irrigation methodologies or devices. Even though the root canal preparation is maintained short of the apical terminus, it causes some extrusion of debris seen by all instrumentation techniques.[789]

A common finding of nearly all the studies in endodontic literature led to a generalized view that the crown-down technique extrudes less debris and irrigants apically as compared to the step-back technique[6] and that a linear filing motion extrudes more debris when compared to instruments used in rotational motion.[10] Within the limitations, all variables were standardized. The study was aimed to observe the influence of rotary and reciprocating files on apical debris extrusion.

As per the results obtained, extrusion of debris apically occurred independent of the type of instrument used. The reciprocating single-file system showed significantly more debris extrusion compared with both the full sequence rotary NiTi instruments [Bar Diagram 1]. The obtained difference may be caused by the preparation technique and/or the cross-sectional designs of the instruments.[11]

Bar Diagram 1

Mean wise distribution of the apical extrusion of debris for all the three groups. (Group C Highest and B Least debris extrusion among the groups)

Flexicon X1 reciprocating system resulted in more debris extrusion because of its positive rake angle[12] and its reciprocating motion. The reason speculated was that a rotary instrument's continuous rotation might improve debris’ coronal transportation by acting as a screw conveyor.[13] Moreover, the reciprocation movement is formed by a wider cutting angle and a smaller release angle. While rotating in the releasing angle, the flutes tend to push the debris more apically. The movement kinematics of the file design is very important in case of debris extrusion. So, in the present study both rotational and reciprocation motion was used.

Flexicon X7 file system showed the least apical extrusion in the current study. This newer file system has a similar cross-sectional design as K3XF files. The absence of radial land, positive rake angle, thicker inner core, asymmetrical parabolic cross-sectional design, and an active cutting tip in combination with sharp cutting edges which cuts effectively.[14] Some authors have stated that reciprocal motion may act as a mechanical piston that increases debris transportation towards the apex about movement kinematics, where continuous rotation provides the coronal transportation of dentin.[1516]

HEDM files showed more extrusion of debris when compared with Flexicon X7. It is probably related due to the absence of radial lands and to their different cross-section and flutes. The larger rectangular cross-section shape of the HEDM file provides more contact area with the root canal wall during preparation and less space for debris accumulation and removal towards the coronal. HEDM file has a varying taper along its axis, should minimize contact between the file and root canal wall debris elimination would be expected to be more efficient compared with the constant tapered file.[17] Due to its negative rake angle[18] its scraping action thus, tends to adhere the root canal walls rather than pushing it coronally. Thus a more considerable amount of debris extruded apically. However, the present study results revealed that varying tapered file (HEDM) left more apical debris extrusion than the constant tapered file (Flexicon X7) and the rake angle of a particular instrument combined with other file designs had influenced apical debris extrusion.

On the other hand, several other studies have obtained different results regarding the amount of debris extruded by reciprocating files. The literature presents controversial results, especially when comparing single reciprocating files and continuous rotation multifile systems in apical extrusion. However, other authors have suggested that reciprocating motion imitates the balanced force technique that causes less debris extrusion.[1920] There are also a few studies reporting no difference in the amount of AED between rotary and reciprocating instrumentation.[21] These results may also be confirmed by the present study's results reporting no significant difference between Flexicon X1 reciprocating files with HEDM and Flexicon X7 rotary files.

These observations are in accordance with previous studies done by Kumar et al. study,[22] who reported that Flexicon X7 rotary movement might cause less debris extrusion as compared to another rotary files systems. However, there is no such statistical significant difference seen in those studies. Till date, there is not enough published data to emphasize the design features of Flexicon files that could affect the apical extrusion of debris, and further research is required in this regard.

While a study by Patel et al.,[23] documented that reciprocating instrumentation produces more apical debris, observed no significant difference in debris extrusion between single-file rotary and reciprocating systems. On the contrary, studies conducted by Uslu et al.[24] showed that single-file reciprocating systems extruded less debris compared to their counterpart rotary systems.

According to this study results, all files caused some degree of extrusion of debris from the apex. This study's contradicting results may be because of differences in methodology, experimental model, and file design used. Because there was no research on this topic in the literature related to the instruments investigated in the present study, a direct comparison could not be made with other studies. Restriction of the Flexicon X1 reciprocating and HEDM rotary file to vital and less infected teeth is one possible measure that can be taken to prevent acute Flare-ups. Similarly, the Flexicon X7 rotary file system can be used for chronic, heavily infected canals and teeth with resorbed apices due to the lower extrusion of apical debris.

Furthermore, studies investigating extrusion of the canal content using extracted teeth have some limitations, and, therefore, the results of these studies should be carefully correlated to real clinical conditions. Further in vivo studies are also required to evaluate post instrumentation pain with these instrumentation systems.

CONCLUSION

Under the limitations of this study, it can be concluded that all instrumentation systems, whether rotary or reciprocating caused apical debris extrusion

Flexicon X7 rotary system was associated with significantly less debris extrusion compared with Flexicon X1 reciprocating and HEDM rotary system and there was no significant difference among all groups

Instrument design and the type of instrument motion (rotary or reciprocating) may have an impact on apical debris extrusion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.