Introduction

Root canal treatment is a fundamental procedure in endodontics aimed at eliminating infection and preventing reinfection of the tooth. The treatment involves chemo mechanical preparation, combining mechanical instrumentation with chemical irrigation to effectively clean and shape the root canal system [1]. The mechani­cal aspect involves the removal of infected dentin, pulp tissue, and microorganisms while creating a suitable shape for subsequent obturation [2].

The apical extrusion of debris and irrigants is a major concern in all root canal treatments. During canal instrumentation, dentin debris, necrotic pulp tissue, micro­organisms, and intracanal irrigants can be extruded through the apical foramen [3]. This extruded material may result in significant inflammatory responses and formation of antigen-antibody complexes, potentially leading to postoperative flare-ups and pain.

Several factors can influence the amount of apically extruded debris during root canal treatment, including working length determination, apical preparation dia­meter, instrumentation technique, and irrigation protocols [4-6]. Numerous studies have demonstrated that all root canal preparation techniques and instruments contribute to some degree of apical debris extrusion [7-9].

Contemporary endodontic practice predominantly utilizes motorized nickel-titanium (NiTi) file systems. The amount of apically extruded debris can be affected by various characteristics of these NiTi files, such as blade design, cross-sectional geometry, taper, tip configuration, metallurgical properties through heat treatment, and kinematics [10].

One Reci (OR; Micro-Mega, Besançon, France) is a heat-treated (C-wire) reciprocating file system, designed to enhance flexibility and maintain canal centering. Its S-shaped cross-section and deep flutes facilitate the coronal displacement of debris while providing efficient cutting with variable centering capability [11].

Revo-S Plus (Micro-Mega, Besançon, France) features an asymmetric NiTi alloy cross-section that reduces stress and increases flexibility. This system incorporates three sharp cutting edges, which facilitate efficient canal penetration and effective removal of debris in the coronal direction [12].

ProTaper Gold (PG; Dentsply, Tulsa, OK, USA) is manufactured using advanced metallurgical heat treatment techniques [13]. It features a convex triangular cross-section and progressive taper design that enhance cutting efficiency and operational reliability.

ProTaper Ultimate (PTUltimate; Dentsply Sirona Endodontics, OK, USA) represents a recent addition to the ProTaper family. It is among the first systems to utilize heat treatment-induced crystallographic phase transformation to optimize the balance between flexibility and strength [14]. This system incorporates three distinct heat treatment technologies across its eight file types, including M-wire (Slider), Gold-wire (SX, Shaper, F1, F2, and F3), and Blue-wire (FX and FXL).

Objectives

This study aimed to compare the amount of apical debris extrusion produced by OR, Revo-S Plus, PG, and PTUltimate files during instrumentation of mesiobuccal canals in mandibular first molars with moderate to severe curvature. The null hypothesis was that there would be no significant difference in the amount of apically extruded debris among the four file systems.

Material and methods

This study was approved by the Non-Interventional Ethics Committee of Pamukkale University on April 18, 2023 (approval number: 07). The research was funded by the Scientific Research Projects Unit of Pamukkale University (project code: 2023DİŞF003), and was conducted at the Endodontic Department of the Faculty of Dentistry at Pamukkale University.

Selection criteria and tooth preparation

Eighty mandibular first molars with mesiobuccal root canal curvatures between 20° and 45° were selected for this study. Radiographic examination was performed in both mesiodistal and buccolingual projections, and a stereomicroscope was used to confirm the presence of two distinct canals in the mesial root. Root canal curvatures were determined using the Schneider method [15].

Exclusion criteria: teeth with incomplete root formation, caries extending to the root, crown or root fractures, previous endodontic treatment, calcified root canals, absence of two mesial canals, and root curvatures less than 20° or greater than 45°.

The patency of apical foramen was verified using a size 10 K-file (Dentac, Istanbul, Turkey). To standardize root lengths, the crowns of all teeth were sectioned at the cementoenamel junction using a diamond bur under water cooling, establishing a standard root length of 17 mm (Figure 1).

Experimental setup preparation

The experimental setup was designed according to the Myers and Montgomery method [16]. Eppendorf tubes were used to collect the irrigation solution and extruded debris. Prior to the experiment, the empty weight of each Eppendorf tube was measured three times using a precision analytical balance (±0.0001 g), and the mean value was recorded. The tooth roots were attached to Eppendorf tubes using cyanoacrylate adhesive.

A 27-gauge needle (Beybi Dental Syringe, Istanbul, Turkey) was positioned alongside the root to equa­lize the internal and external pressure within the tube. The entire apparatus was secured within a glass vial and covered with aluminum foil to prevent operator bias during the instrumentation procedure (Figure 2).

Irrigation procedures

To ensure standardization of irrigation delivery, a serum infusion pump (SN-1600V, Shenzhen, China) was employed. Distilled water was selected as the irrigation solution and delivered at a constant rate of 1 ml/min. A 30-gauge side-vented irrigation needle positioned 2 mm short of the working length was used for all irrigation procedures.

Root canal shaping

The selected 80 teeth were randomly allocated to four experimental groups (n = 20 per group). Initial canal negotiation for all mesiobuccal canals was performed using a size 15 K-hand file. Irrigation with 1 ml of distilled water was performed after each file change or after three pecking motions. Debris accumulated on the files was removed using moist gauze, and a total of 5 ml of distilled water was applied for irrigation during the entire shaping procedure. Following canal preparation, an additional 1 mL of distilled water was used to flush any remaining debris into the Eppendorf tube. Canal patency was verified with a size 10 K-file after each instrument change.

The experimental groups were instrumented as follows:

• Group 1 (OR): Instrumentation was performed using Red Ai Endomotor (Woodpecker) in reciprocating motion, with angles of 60° clockwise and 170° counterclockwise, as recommended by the manufacturer.

• Group 2 (Revo-S Plus): Instrumentation was performed using Red Ai Endomotor at 300 rpm and 2.5 Ncm
torque. A SC1 file was used to prepare the coronal two-thirds of the canal, while SC2 and SU files were employed to instrument to the full working length.

• Group 3 (PG): Instrumentation was performed at 300 rpm and 2 Ncm torque. A SX file was used to enlarge the coronal third, followed by S1 and S2 files to the working length. Final canal shaping was completed using F1 and F2 finishing files.

• Group 4 (PTUltimate): Instrumentation was performed at 400 rpm and 2 Ncm torque. Shaper and Slider files were used to prepare to the working length, followed by F1 and F2 finishing files for final canal shaping.

Weight measurement of extruded debris

All procedures were performed by a single expe­rienced operator to ensure standardization. Following root canal preparation, the teeth were carefully removed from the Eppendorf tubes. The tubes containing extruded debris and distilled water were placed into an incubator at 37°C for 14 days to allow complete evaporation of moisture and determination of the dry weight of extruded debris. After the evaporation period, each Eppendorf tube was weighed three times using a precision analytical balance, and the mean value was calculated. The weight of apically extruded debris was determined by subtracting the initial weight of the empty Eppendorf tube from the final weight (Figure 3).

Statistical analysis

Statistical analysis was performed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA), while the Shapiro-Wilk test was used to assess the normality of data distribution. Since the data did not follow a normal distribution, the Kruskal-Wallis H test was applied to compare the amounts of extruded debris between the four file systems. The significance level was set at p < 0.05 for all analyses.

Results

The comparison of debris extrusion amounts between the four file systems is presented in Table 1.

The results indicated no statistically significant difference in the mean amounts of apically extruded debris between the four groups (p > 0.05). Although not statistically significant, the PG and PTUltimate groups demonstrated lower mean values of debris extrusion compared to the OR and Revo-S Plus groups. Pairwise comparisons between individual file systems were not performed due to the absence of significant differences in the Kruskal-Wallis analysis. The mean values of apically extruded debris for each file system are illustrated in Figure 4.

Discussion

Chemo mechanical preparation is a critical phase of endodontic treatment. It involves the use of endodontic instruments and irrigation solutions to effectively eliminate organic and inorganic tissues, microorga­nisms, and their byproducts from the root canal system [17]. During this process, debris and irrigation solutions may be inadvertently extruded beyond the apical foramen, potentially causing periapical inflammation, postoperative pain, and delayed healing [1].

In the present study, four contemporary NiTi file systems, i.e., OR, Revo-S Plus, PG, and PTUltimate were evaluated for their propensity to extrude debris apically during instrumentation of curved root canals. The findings revealed that all file systems resulted in measurable apical extrusion of debris, with no statistically significant differences observed among the systems (p > 0.05). Therefore, based on these results, the null hypothesis was accepted.

The PTUltimate system features an asymmetric pa­rallelogram cross-section that reportedly allows the files to advance through the canal with a snake-like motion, potentially enhancing debris removal efficiency [14]. PG files, with their convex triangular cross-section and variable helical angle, have been reported to exhibit enhanced resistance to cyclic fatigue and increased flexi­bility, which may contribute to more controlled instrumentation and potentially reduced debris extrusion [13]. The OR system, a heat-treated reciprocating file, offers advantages, including increased bending strength, improved resistance to cyclic fatigue, and reduced modulus of elasticity. Its variable and asymmetric cross-section is designed to enhance cutting efficiency while facilitating debris removal [14]. Revo-S Plus files feature an asymmetric cross-section with three sharp cutting edges, designed to facilitate efficient canal penetration and coronal displacement of debris [12]. Despite these design differences, our findings suggest that the metal­lurgical properties and geometric designs of these file systems do not significantly influence the amount of apically extruded debris during instrumentation of curved canals.

Numerous studies have demonstrated that all root canal preparation techniques and instruments inevitably result in some degree of apical debris extrusion [8, 9, 14, 18]. Al-Omari and Dummer [18] reported that linear filing techniques, such as the step-back method, produced greater amounts of apical debris extrusion compared to rotational techniques. In contemporary endodontic practice, motorized NiTi files have largely replaced manual instrumentation techniques. The amount of apically extruded debris can be influenced by various characteristics of these NiTi files, such as blade design, cross-sectional geometry, taper, metallurgical properties, heat treatment, and kinematics [10].

The influence of reciprocating versus rotary motion on debris extrusion has been extensively investigated [19-24]. Küçükyılmaz et al. [19] found no statistically significant differences in debris extrusion among Reciproc (VDW, Munich, Germany), OneShape (Micro-Mega, France), and ProTaper files. Similarly, Al-Omari et al. [20] found no significant differences between reciprocating and rotary systems, which aligns with our findings. However, some studies have reported conflicting results. Uzun et al. [21] observed that Reciproc files produced the least amount of extruded debris, while Bürklein et al. [22] reported that Reciproc files extruded the most debris compared to F360 (Brasseler, Lemgo, Germany), OneShape, and Mtwo (VDW, Munich, Germany) files. These varying results suggest that the relationship between file kinema­tics and apical debris extrusion is complex and may be influenced by multiple factors.

Eskibağlar et al. [23] compared debris extrusion among three rotary file systems, including PTUltimate (25.08 taper), TruNatomy (26.04 taper; TRN, Dentsply Sirona, Switzerland), and VDW.Rotate (25.06 taper; VDW.R, Munich, Germany), and found no statistically significant differences. However, they observed that VDW.R files produced the least debris extrusion, while PTUltimate files produced the most. The researchers attributed these differences to variations in file taper and the influence of Van der Waals forces on the thinner TRN files. In our study, we utilized files with varying tapers, but found that taper was not a significant factor in determining the amount of extruded debris.

Yılmaz Çırakoglu and Özbay [24] reported that TruNatomy files produced significantly less apical debris compared to ProTaper Next (PTN), PG, and TRN rotary files, although no significant differences were observed among PG, TRN, and PTN files. Moreover, Cakici et al. [25] reported that ProTaper Universal (PTU) produced significantly more apical debris in curved canals compared to PG, PTU, PTN, and Reciproc files, with PG files producing significantly less debris than other systems. In our study, though not statistically significant, PG and PTUltimate files demonstrated lower mean values of apical debris extrusion compared to OR and Revo-S Plus files. This trend might be attributed to the specific design features of these files, including the asymmetric parallelogram cross-section of PTUltimate files, convex triangular cross-section of PG files, and the gold heat treatment technology that enhances their mechanical properties [13, 14].

For our experimental setup, we adapted the metho­dology described by Myers and Montgomery [16]. While this approach is widely used in apical extrusion studies, it has certain limitations. Critics have highlighted that this model does not account for periapical tissue resistance, does not preserve the natural state of the apical constriction, and does not provide a physical barrier to limit debris extrusion [16, 26]. Some researchers have proposed alternative setups, which incorporate materials to simulate periapical tissues. Hachmeister et al. [27] and Altundasar et al. [28] utilized floral foam as an apical barrier, although this material can absorb debris and irrigation solution, potentially affecting measurements. Other studies have employed 1.5% agar gel with a density similar to periapical tissues, but the thickness of this barrier may not accurately represent clinical variations in periapical conditions (such as granulomas or cysts) and is difficult to standardize [29].

It is important to acknowledge that while quantitative measurement of extruded debris provides valuable information, it does not assess the virulence or antigenicity of the extruded material. The clinical significance of debris extrusion may depend not only on the quantity of extruded material but also on its biological properties and the host’s immune response [30]. Additionally, the experimental procedure is technique-sensitive, and factors, such as handling of the Eppendorf tubes, can potentially influence weight measurements [31].

In clinical practice, sodium hypochlorite is the most commonly used irrigation solution. However, for experi­mental purposes, distilled water was selected as the irrigation solution in our study, as sodium hypochlorite can form crystals upon evaporation, potentially leading to inaccurate weight measurements [32].

While many studies on apical debris extrusion have utilized single-rooted teeth due to their simplicity and standardization potential [33], we chose to use mandibular first molars with curved mesiobuccal canals to simulate clinical challenges more closely. Previous stu­dies have demonstrated that tooth type and canal anatomy significantly influence apical extrusion [34, 35]. Karataşlıoğlu et al. [36] reported that the degree of root canal curvature has a significant impact on the amount of apically extruded debris. By utilizing mesiobuccal canals with curvatures ranging from 20° to 45°, our study provides clinically relevant information regarding debris extrusion in challenging anatomical situations.

This study has several limitations that should be acknowledged. First, the experimental setup, while widely accepted, does not fully replicate the clinical environment, particularly the absence of periapical tissue resistance that might limit debris extrusion in vivo. Second, the use of distilled water instead of sodium hypochlorite, although methodologically necessary, it represents a deviation from clinical practice. Third, the study evaluated only quantitative aspects of debris extrusion without considering qualitative factors, such as biological properties of extruded material. Finally, despite our efforts to standardize the procedures, variations in canal anatomy and operator technique may have influenced the results. Future studies should focus on developing more clinically relevant mo­dels for evaluating debris extrusion and investigating the biological implications of the extruded material.

Conclusions

Within the limitations of this in vitro study, all four file systems (i.e., OR, Revo-S Plus, PG, and PTUltimate) resulted in apical extrusion of debris during instrumentation of curved root canals, with no statistically significant differences observed among the systems (p > 0.05). These findings suggest that clinicians should be aware of the potential for apical extrusion regardless of the file system selected, and should implement strategies to minimize its occurrence and potential clinical consequences.

Disclosures

Author contributions: Conceptualization: H.K.A, İ.F.E; Methodology: P.C.A., I.F.E.; Questionnaire adaptation: P.C.A.; Investigation and data collection: H.K.A., İ.F.E.; Formal analysis: H.K.A., I.F.E.; Data curation: H.K.A.; Writing of original draft: H.K.A., İ.F.E.; Writing – review and editing: H.K.A.; Supervision: İ.F.E.; Project administration: H.K.A. All authors have read and agreed to the published version of the manuscript.

Funding: This work was funded by Pamukkale University Scientific Research Projects Unit under project code 2023DİŞF003.

Institutional Review Board statement: This study was approved by Pamukkale University Non-Interventional Ethics Committee on April 18, 2023, approval number: 07.

Informed consent statement: Not applicable.

Data availability statement: All the data generated or analyzed in this study are included in this manuscript. The data generated in this study may be requested from the corresponding author.

Acknowledgments: None.

Conflicts of interest: The authors declare no conflicts of interest.

AI use statement: Not applicable.

References