Extrusion of debris during retreatment using various nickel-titanium files in teeth with simulated lateral root perforation

Abstract

Purpose: To investigate the influence of various nickel-titanium (Ni-Ti) files on debris extrusion during the retreatment of teeth with simulated lateral root perforation, focusing on root resorption.

Methods: Sixty human mandibular premolar teeth were divided into groups with and without perforation and further subdivided based on the retreatment technique. Lateral root perforations were created in one group (Group 1), while the other group had no perforations (Group 2). Two retreatment techniques were compared: Remover (RE)+One RECI (OR) and ProTaper Universal Retreatment (PTUR)+WaveOne Gold (WOG). The weight of the extruded debris was determined. The time of both retreatment procedures was measured. Statistical analyses were performed using a two-way analysis of variance (ANOVA) test (P < 0.05).

Results: Teeth with simulated lateral root perforation exhibited higher extrusion of debris during retreatment. In both groups, RE+OR files led to more extruded debris than PTUR+WOG files. However, this difference was statistically significant in Group 2 (P < 0.001). Compared to PTUR+WOG files, RE+OR files showed a statistically significant longer time to remove obturation material (P < 0.001).

Conclusion: Perforated teeth exhibited significantly higher debris extrusion. While both file systems demonstrated similar debris extrusion in perforated teeth, the RE+OR files significantly increased debris extrusion in non-perforated teeth compared to the PTUR+WOG files.

Introduction

Root perforation (RP) occurs when there is mechanical or iatrogenic communication between the root canal space and the periodontal area, exposing the periodontium to the oral cavity [1]. This exposure leads to bacterial contamination of the supporting tissues of the teeth. RP can be a consequence of internal or external root resorption (ERR). Notably, this condition is identified in 2% to 12% of endodontically treated teeth and is responsible for 10% of periradicular tissue failures [2,3,4].

The failure of initial endodontic treatment can be attributed to a range of causes, such as the persistence of microorganisms due to insufficient biomechanical preparation, inadequate obturation, or an improper coronal seal. In such instances, non-surgical endodontic retreatment is the preferred initial approach to decrease or eradicate microbial infection within the root canal space [5]. This procedure aims to reestablish the health of the periapical tissues by removing the root filling material, thoroughly cleaning the root canal system, and subsequently refilling it. During the root canal preparation and retreatment, there is a potential risk of pushing dentin chips, bacteria, pulp tissue, and irrigation solutions toward the peri-radicular area. This extrusion may lead to inflammation, postoperative discomfort, and prolonged recovery in the periapical area [6,7,8,9]. A previous study [10] on the process of root canal retreatment found that a tooth with simulated apical root resorption experienced significantly greater extrusion of debris compared to a tooth without apical root resorption.

Significant developments in instrument properties have resulted in the emergence of several instrumentation systems for root canal preparation and retreatment.

One RECI (OR; Micro-Mega, Besançon, France) is a single-file system with a heat-treated C-wire. It has a variable, off-centered cross-section, and the tip of the file initiates as a triple helix and gradually transforms into an S-shape towards the shank. OR file is operated in a reciprocating motion with specific angles, which include 170º counterclockwise (CCW) and 60º clockwise (CW) rotations to achieve a cutting action in the CCW direction. It is available in 5 sizes: #20.04, #25.04, #25.06, #35.04, and #45.04 [11].

The MicroMega Remover (RE) (#30.07), manufactured by MicroMega in Besançon, France, is a specialized file explicitly designed to eliminate gutta-percha material during non-surgical endodontic retreatment. The file is used with a back-and-forth motion without any apical pressure and is 3 mm shorter than the working length (WL) if there is a complete obturation or until the first obturation. It is possible to use a brushing motion.

ProTaper Universal Retreatment file system (PTUR; Dentsply Maillefer, Baillagues, Switzerland) has three files, namely D1 (#30.09), D2 (#25.08), and D3 (#20.07). WaveOne Gold (WOG; Dentsply Sirona, Ballaigues, Switzerland) is a single-file system characterized by a semiactive tip, variable tapers, and a parallelogram cross-section. It is available in four different sizes (small: #20.07, primary: #25.07, medium: #35.06, large: #45.05) [12]. Investigating the impact of different nickel-titanium (Ni-Ti) file systems on debris extrusion during the retreatment of teeth with perforated root resorption may help alleviate potential adverse effects on periapical tissues. Currently, there is a lack of studies assessing the amount of debris extrusion during the retreatment process in teeth with simulated lateral root perforations using RE and OR files. Comparing these findings with outcomes from various Ni-Ti file systems could provide valuable insights.

The null hypothesis is that the file systems used for retreatment and whether or not there is lateral root perforation do not affect the amount of debris. The objective of the present study was to evaluate and compare the amount of extruded debris produced during the removal of obturation material from canals with simulated lateral root perforation using different Ni-Ti files.

Materials and Methods

Sample size calculation

This study protocol received approval from the Clinical Research Ethics Committee of Akdeniz University, with the decision number KAEK 612. The sample size calculation was carried out using G*Power version 3.1 software (Heinrich Heine Universität Düsseldorf, Düsseldorf, Germany). An effect size of 0.4, a power of 0.85, and an alpha error of 0.05 were employed for the determination.

Sample selection

In this study, a total of sixty human mandibular premolar teeth were chosen. Following radiographic examinations, teeth with resorption, calcification, a root canal filling, an open apex, or a root canal curvature greater than 10° were eliminated from this study. Furthermore, teeth with fractures or cracks were not evaluated for inclusion. All residual tissue on the teeth was thoroughly removed mechanically. Using a diamond fissure bur, all the crowns of selected samples were partially eliminated under water and air cooling to establish a reference plane and attain a standard WL of 17 ± 1 mm. WL was established as 1 mm shorter than the point at which a size 10 K-file first became visible at the apex when observed through a stereomicroscope (Stemi 508, Zeiss, Oberkochen, Germany). In addition, the diameter of the foramen in all teeth was standardized to a size 15 K-file. For the instrumentation procedure,WOG Primary (#25.07) files were used. Following each third pecking motion, the root canal was irrigated with 2 mL of 2.5% NaOCl and 2 mL of sterile saline solution. For the final stage of irrigation, 2.5 mL of 17% ethylenediaminetetraacetic acid (EDTA) solution was administered for 1 min, followed by 5 mL of sterile saline solution. Then, the prepared root canals were dried using paper points.

Preparation of the perforation area and obturation

A technique of warm vertical compaction was used to fill all root canals of the samples (Woodpecker Fi-P& Fi-G Gutta-Percha Obturation System, Woodpecker Medical Instrument Co., Guilin, PR China). WOG Primary (#25.07) gutta-percha (Dentsply Maillefer) and Dia-Proseal (Diadent, Cheongju, Republic of Korea) sealer, which was applied with the master cone, were used to obturate the apical part. Within 4-5 mm of the WL, gutta-percha was cut with a Fi-P obturation pen, and the remaining area of root canals was filled with a Fi-G obturation gun. The homogeneity of the root canal filling was checked with the periapical radiograph. To facilitate the setting of the sealer, all the samples were preserved for a week at 37°C and 100% humidity.

The study included 60 teeth, with 30 teeth in Group 1 and 30 teeth in Group 2. In Group 1, a simulated lateral root perforation was intentionally generated in the apical 1/3 of the root, 3 mm above the root apex. Diamond burs with a 1 mm diameter were employed to create a perforation that extended to the root canal filling. A perforation was created perpendicular to the lateral root surface to mimic an area of perforation caused by external root resorption in a standard size. For Group 2, comprising the remaining 30 teeth, no root perforation was created. Subsequently, both Group 1 and Group 2 were further divided into two sub-groups, each consisting of 15 teeth. The subdivision was based on the retreatment technique to be applied in the subsequent phases of the study.

In the initial pilot study, a considerable amount of irrigation solution was observed to be extruded from the perforated areas. To measure the quantity of extruded debris, an improved version of the experimental setup outlined in Myers and Montgomery's study was employed. [13]. The extruded debris was gathered in glass vials. Accuracy was ensured by employing an analytical balance (Shimadzu AP225WD, Kyoto, Japan) with a precision of 10⁻⁵ g. The empty glass vials were weighed three times, and the average value was recorded. The stoppers of the glass vials were meticulously perforated to facilitate the insertion of the teeth into these holes. To equalize pressure within and outside the vials, a 27-gauge needle was placed through the plastic stopper. To maintain operator blindness in the study, the glass vials were covered with aluminum foil (Fig. 1).

The removal of the obturation material was performed in accordance with the same methods in both Groups 1 (teeth with lateral root perforation) and 2 (teeth without perforation), as described below.

Fig. 1 Experimental setup of the study

Remover + One RECI subgroup

According to the instructions of the manufacturer, the One Flare (Micro-Mega) file was used before the RE file at the beginning of retreatment. Then RE (#30.07) was used with a back-and-forth motion and was 3 mm shorter than the WL. One Flare and RE files were used at 2.5 Ncm torque and 400 rpm speed. Finally, apical preparation was completed with OR #35.04, and #45.04 at 400 rpm / 4 Ncm as suggested by the manufacturer using the Dentsply X-Smart Plus (Densply Maillefer) endodontic motor. During the procedure, between the One Flare and RE files, and after the progressive movement in three waves (3 up-and-down movements) of the OR #35.04 and #45.04 files, 2.5 mL of distilled water was used.

ProTaper Universal Retreatment + WaveOne Gold subgroup

The retreatment procedure was applied using PTUR files (D1, D2) in a progressive crown-down manner. D1 (#30.09) and D2 (#25.08) files were used at the coronal and middle third of root canals, respectively. Apical preparation was finished with WOG Medium (#35.06), and WOG Large (#45.05). WOG files were used as suggested by the manufacturer in the ‘Wave One All’ mode of a Dentsply X-Smart Plus endodontic motor. During the retreatment procedure, 2.5 mL of distilled water was used between the D1 and D2 retreatment files, and after each 3 mm up-and-down movement of the WOG Medium and Large files.

For the irrigation procedure, a total of 15 mL of distilled water was used with a 30-gauge double-sided port needle (Osaka Dental, Guangdong, PR China), employing back-and-forth movements. After every removal from the root canal, the flutes of the files were cleaned. The retreatment procedure was considered finished when the final file reached the designated WL, with no remaining filling material on the file, and when the canal walls were confirmed to be smooth and free of debris. To eliminate any potential variations between operators, all procedures were conducted by a single experienced specialist, who performed the process under a dental operating microscope.

The time required for retreatment was carefully recorded in seconds. Following the retreatment procedure, the stopper, needle, and tooth were removed from the glass vial.To collect debris from the outer surface of the root, the root was washed inside the vial with 1 mL of distilled water. These vials were subsequently placed in an incubator set at 37°C for 14 days to allow the distilled water to evaporate. After this incubation period, three separate weight measurements were performed on the vials as before, and then the average value was calculated. To find the dry weight of the extruded debris, the weight of the empty vial was subtracted from the weight of the vial containing the debris.

Statistical analysis

Normality assessment of the debris extrusion data with the Shapiro-Wilk test revealed a non-parametric distribution and significant positive skewness. To mitigate this skewness, a logarithmic transformation was applied. Following transformation, the data displayed parametric normality. Leven's test was used to ensure homogeneity of variance. This comprehensive approach validates the data's appropriateness for subsequent parametric statistical analyses. The impact of the used files and the presence of perforation on debris extrusion was assessed using a two-way analysis of variance (ANOVA) test. Statistical analyses were conducted using Jamovi software (Version 2.3.28.0). Significance was determined at a threshold of P < 0.05.

Results

Table 1 presents the mean values for the weight of extruded debris and time for each group. Teeth with simulated lateral root perforations showed a higher weight of extruded debris during retreatment compared to teeth without root perforations (P < 0.001). In Group 1 (teeth with lateral root perforation), no significant difference was found in terms of extruded debris between RE+OR files and PTUR+WOG files (P = 0.997).

However, in Group 2 (teeth without perforation), the amount of apically extruded debris during retreatment was significantly greater with RE+OR files compared to PTUR+WOG files (P < 0.001). PTUR+WOG files resulted in significantly more debris extrusion in Group 1 (teeth with lateral root perforation) than in Group 2 (teeth without perforation) (P < 0.001). There was no statistically significant difference observed in the amount of extruded debris by RE+OR files when comparing Groups 1 and 2 (P = 0.110). Furthermore, RE+OR files demonstrated a statistically longer time in removing root canal filling material compared to PTUR+WOG files (P < 0.001).

Table 1 Mean and standard deviation (SD) values for the weight of extruded debris (g) and time (s) required to remove canal filling material

	Preparation technique
Groups	RE+OR files			PTUR+WOG files
	n	Mean ± SD	t (s)	n	Mean ± SD	t (s)
Group 1	15	0.00196 ± 0.0012a,A	338 ± 67x	15	0.00168 ± 0.00079a,A	219 ± 35y
Group 2	15	0.00123 ± 0.00127a,A		15	0.00050 ± 0.00057b,B

Group 1: teeth with lateral root perforation; Group 2: teeth without perforation. In each column, different lower-case letters show a statistically significant difference at the (0.05) level. Different capital letters indicate a statistically significant difference at the (0.05) level in each row: t (s), the time needed to complete the removal of root canal filling material.

Discussion

Non-surgical endodontic retreatment is necessary when initial treatment fails due to issues such as persistent bacteria, insufficient treatment, coronal leakage, overextensions of filling materials, untouched canals, or complications from instrumentation. During primary and retreatment, various substances may extrude beyond the apical foramen, triggering an inflammatory response around the apical region [14,15,16].

The objective of this study was to assess the weight of extruded debris produced during retreatment utilizing different Ni-Ti files in teeth with simulated lateral root perforation. All tested groups exhibited debris extrusion. The present study revealed significant differences in the weight of extruded debris during retreatment procedures using different Ni-Ti files in teeth, with or without root perforation, and the null hypothesis was rejected.

Debris extrusion was more pronounced in Group 1 (teeth with lateral root perforation) using both RE+OR and PTUR+WOG files compared to Group 2 (teeth without perforation). Specifically, the PTUR+WOG files showed a significant difference in debris extrusion between the two groups. The WOG Medium File, with an ISO 35 tip size and 6% continuous taper in the first 3 mm (D1-D3), and the WOG Large File, with an ISO 45 tip size and 5% continuous taper in the same region, demonstrated a tapered design with decreasing percentage from D4 to D16. The parallelogram off-section design limits the file's contact with dentin to one or two points, creating extra space around the instrument. This design feature aids in debris removal from the coronal part of the canal during preparation, potentially contributing to increased debris extrusion in the lateral perforation area situated 3 mm above the root tip. In the study by Kharouf et al. [17], the apically extruded debris in curved root canals during primary endodontic treatment was measured. Various irrigation solutions and files with different kinematics (OR, WOG, and ProTaper Next (PTN) with continuous and reciprocal motion) were used. According to their findings, OR files statistically caused the least amount of debris extrusion in all groups. However, in the current study, RE+OR files resulted in the highest debris extrusion in both Groups 1 (teeth with lateral root perforation) and 2 (teeth without perforation). This discrepancy may be attributed to the use of additional files during retreatment and the presence of perforation, which could have contributed to the increased debris extrusion in the current study.

Despite having fewer tapers than WOG Medium and Large files, OR files (4%) caused more debris to extrude in both groups. This may be due to the reciprocal angle of an OR file. The reciprocal angles of the OR files are 170° CCW-60° CW, whereas the WOG files are 150° CCW-30° CW. Arslan et al. [18], conducted a comparative study to assess the extruded debris when employing Reciproc (RCP) instruments with varying angles and kinematics. The reciprocating motions with a 150° CCW-30° CW angle produced the least amount of debris when compared to the other groups. The findings of this study are similar to the results of the present study.

In a study conducted by Koşar et al. [19], the amount of debris extruded during retreatment procedures using various file systems (Genius, RCP Blue, PTN, Tango-Endo, and Twisted File Adaptive) in combination with different kinematic movements was compared. They stated that an increased interval between reciprocation angles acted like a screw conveyor, reducing apically extruded debris. Consistent with this study, the increased interval between reciprocation angles in WOG files may have led to statistically less debris extrusion compared to OR files in Group 2 (teeth without perforation). Since there is no research examining the effect of RE+OR files on the amount of debris extruded during retreatment in teeth with lateral root perforation, there is no data available for comparison.

In this study, PTUR+WOG files required less time than RE+OR files to remove root canal filling. The larger diameter of the WOG file may have decreased preparation time by permitting the removal of more root canal filling material.

In clinical practice, endodontic retreatment is usually finished using files with larger apical diameters than the master apical file preferred for primary canal preparation. Therefore, size 45 files were used for additional instrumentation in the current study. Only the D1 and D2 files of the PTUR files were utilized for retreatment procedures to ensure standardization because the RE files used were 3 mm shorter than the WL in accordance with the manufacturer.

Due to the large quantity of distilled water that extruded from the perforation area during the pilot study, Myers and Montgomery’s experimental setup was modified for the present study, and debris was collected in glass vials. The microhardness of dentin varies with age, potentially influencing the amount of extruded debris. Considering that the teeth utilized in this study were extracted due to periodontal reasons, the sample population is likely to consist predominantly of middle-aged or elderly patients. To simulate periapical tissues in investigations on debris extrusion, floral foam [20], agar gel [21], and silicon material [22] were used. Nevertheless, none of these techniques could precisely reflect the periapical tissues. As a result, the apical barrier was not used in this study. The irrigation solution used could influence the study’s findings [23]. Distilled water was used as the irrigation solution since the crystal formation generated by the use of NaOCl may impact the amount of extruded debris. It is important to emphasize that this study primarily aimed to thoroughly evaluate the amount of debris extrusion when utilizing four different Ni-Ti files for obturation material removal. It is crucial to recognize that the results discussed here solely pertain to Ni-Ti files and do not include any observations regarding hand files. Consequently, the outcomes obtained from hand file usage may differ significantly. All of the above points present possible limitations for the present study, and further in vivo research is required to support the current investigation.

In conclusion, significant differences in debris extrusion during endodontic retreatment with various Ni-Ti files were found. Teeth with simulated lateral root perforations showed higher debris extrusion compared to those without perforation. While there was no significant difference in debris extrusion between file systems in perforated teeth, the RE+OR files resulted in more debris extrusion in non-perforated teeth. Also, RE+OR files took longer for retreatment compared to PTUR+WOG files.

Unsuccessful endodontic therapy can lead to an inflammatory process that causes root resorption, resulting in root perforation. Clinicians should consider this treatment since it may result in a higher amount of debris being pushed out upon retreatment, potentially reducing the healing capacity of nearby tissue.

Abbreviations

ANOVA: analysis of variance; CCW: counterclockwise; CW: clockwise; EDTA: ethylenediaminetetraacetic acid; ERR: external root resorption; Ni-Ti: nickel-titanium; OR: One RECI; PTN: ProTaper Next; PTUR: ProTaper Universal Retreatment; RCP: Reciproc; RE: Remover; RP: root perforation; WOG: WaveOne Gold; WL: working length

Ethical Statements

This study protocol received approval from the Clinical Research Ethics Committee of Akdeniz University, with the decision number KAEK 612.

Conflicts of Interest

The authors have no conflict of interest relevant to this article.

Funding

None

Author Contributions

HH: conceptualization, investigation, methodology, project administration, data curation, formal analysis, writing original draft, review, and editing; SK: investigation, methodology, writing, review, and editing; AK: supervision, review, and editing

ORCID iD

HH: [e-mail], https://orcid.org/0000-0003-4073-8387

SK*: [e-mail], https://orcid.org/0000-0002-9446-5655

AK: [e-mail], https://orcid.org/0000-0002-4942-3739

Acknowledgments

There are no acknowledgments to be described.

Data Availability Statements

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

• 1.  Maseratt V, Ebrahimi HS, Saberi EA, Pirhaji A, Khosravil N (2020) Diagnostic accuracy of two cone-beam computed tomography systems for detection of strip perforation in the mesial root of mandibular molars. G Ital Endod 34, 63-68. doi: 10.32067/GIE.2020.34.01.01
• 2.  Haghanifar S, Moudi E, Mesgarani A, Bijani A, Abbaszadeh N (2014) A comparative study of cone-beam computed tomography and digital periapical radiography in detecting mandibular molars root perforations. Imaging Sci Dent 44, 115-119. doi: 10.5624/isd.2014.44.2.115
• 3.  Shokri A, Eskandarloo A, Noruzi-Gangachin M, Khajeh S (2015) Detection of root perforations using conventional and digital intraoral radiography, multidetector computed tomography and cone beam computed tomography. Restor Dent Endod 40, 58-67. doi: 10.5395/rde.2015.40.1.58
• 4.  Adibi A, Sobhnamayan F, Ostovar Zijerdi N, Tajik M, Paknahad M (2022) Comparison of the accuracy of CBCT images and apex locator in detection of external root resorption with perforation. J Dent (Shiraz) 23, 445-451. doi: 10.30476/DENTJODS.2021.91056.1548
• 5.  Giuliani V, Cocchetti R, Pagavino G (2008) Efficacy of ProTaper universal retreatment files in removing filling materials during root canal retreatment. J Endod 34, 1381-1384. doi: 10.1016/j.joen.2008.08.002
• 6.  Kuştarcı A, Akpınar KE, Er K (2008) Apical extrusion of intracanal debris and irrigant following use of various instrumentation techniques. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 105, 257-262. doi.org/10.1016/j.tripleo.2007.06.028
• 7.   Kuştarcı A, Akpınar KE, Sümer Z, Er K, Bek B (2008) Apical extrusion of intracanal bacteria following use of various instrumentation techniques. Int Endod J 41, 1066-1071. doi.org/10.1111/j.1365-2591.2008.01470.x
• 8.  Kirchhoff AL, Fariniuk LF, Mello I (2015) Apical extrusion of debris in flat-oval root canals after using different instrumentation systems. J Endod 41, 237-241. doi.org/10.1016/j.joen.2014.09.023
• 9.  Alves FR, Marceliano-Alves MF, Sousa JC, Silveira SB, Provenzano JC, Siqueira JF Jr (2016) Removal of root canal fillings in curved canals using either reciprocating single-or rotary multi-instrument systems and a supplementary step with the XP-Endo Finisher. J Endod 42, 1114-1119. doi.org/10.1016/j.joen.2016.04.007
• 10.  Topçuoğlu H, Demirbuga S, Topçuoğlu G (2020) Evaluation of apically extruded debris during the removal of canal filling material using three different Ni‐Ti systems and hand files in teeth with simulated apical root resorption. Int Endod J 53, 403-409. doi.org/10.1111/iej.13234
• 11.  Reynette C, Giess R, Davril J, Martrette JM, Mortier É, Balthazard R et al. (2023) Influence of endodontic motors on the behaviour of root canal shaping instruments: an in vitro comparative study. BDJ Open 9, 51. doi: 10.1038/s41405-023-00179-z
• 12.  Gündoğar M, Özyürek T (2017) Cyclic fatigue resistance of OneShape, HyFlex EDM, WaveOne Gold, and Reciproc Blue nickel-titanium instruments. J Endod 43, 1192-1196. doi.org/10.1016/j.joen.2017.03.009
• 13.  Myers GL, Montgomery S (1991) A comparison of weights of debris extruded apically by conventional filing and Canal Master techniques. J Endod 17, 275-279. doi.org/10.1016/S0099-2399(06)81866-2
• 14.  Seltzer S, Naidorf IJ (1985) Flare-ups in endodontics: I. Etiological factors. J Endod 11, 472-478. doi.org/10.1016/S0099-2399(85)80220-X
• 15.  Tabassum S, Khan FR (2016) Failure of endodontic treatment: the usual suspects. Eur J Dent 10, 144-147. doi.org/10.4103/1305-7456.175682
• 16.  Zhang Q, Gu J, Shen J, Ma M, Lv Y, Wei X (2023) Apically extruded debris, canal transportation, and shaping ability of nickel-titanium instruments on contracted endodontic cavities in molar teeth. J Oral Sci 65, 203-208. doi.org/10.2334/josnusd.23-0050
• 17.  Kharouf N, Pedullà E, Nehme W, Akarma K, Mercey A, Gros CI et al. (2022) Apically extruded debris in curved root canals using a new reciprocating single-file shaping system. J Endod 48, 117-122. doi.org/10.1016/j.joen.2021.10.002
• 18.  Arslan H, Doğanay E, Alsancak M, Çapar ID, Karataş E, Gündüz HA (2016) Comparison of apically extruded debris after root canal instrumentation using Reciproc® instruments with various kinematics. Int Endod J 49, 307-310. doi.org/10.1111/iej.12449
• 19.  Koşar T, Çelik D, Taşdemir T (2023) Apically extruded debris of different file systems used with various kinematic movements during retreatment: an in vitro study. Aust Endod J 49, 33-40. doi.org/10.1111/aej.12690
• 20.  Altundasar E, Nagas E, Uyanik O, Serper A (2011) Debris and irrigant extrusion potential of 2 rotary systems and irrigation needles. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 112, e31-e35. doi.org/10.1016/j.tripleo.2011.03.044
• 21.  Lu Y, Wang R, Zhang L, Li HL, Zheng QH, Zhou XD et al. (2013) Apically extruded debris and irrigant with two N i‐T i systems and hand files when removing root fillings: a laboratory study. Int Endod J 46, 1125-1130. doi.org/10.1111/iej.12104
• 22.  Yılmaz K, Özyürek T (2017) Apically extruded debris after retreatment procedure with Reciproc, ProTaper Next, and Twisted File Adaptive instruments. J Endod 43, 648-651. doi.org/10.1016/j.joen.2016.12.003
• 23.  Parirokh M, Jalali S, Haghdoost AA, Abbott PV (2012) Comparison of the effect of various irrigants on apically extruded debris after root canal preparation. J Endod 38, 196-199. doi.org/10.1016/j.joen.2011.10.027