Assessment of smear layer removal utilizing a conservative root canal instrumentation technique involving magnetically agitated irrigation with iron paramagnetic nanoparticles

Abstract

Background

The development of new instrument designs for mechanically shaping root canal walls does not completely clean all the root space, because of the disparity between the complexities of canal anatomy and instrument design. This study aimed to determine the optimum effect of iron oxide nanomagnet particles (IONPs) in cleaning the surface of the root canal and open dentin tubules, as well as analyze the dispersion of iron ions on the dentinal walls.

Materials and methods

Sixty intact extraction teeth were used and divided into six groups as stated by agitation protocol of irrigant: Group 1: Control, Group 2: Normal saline with ultrasound, Group 3: IONP with ultrasound. Group 4: IONP with magnetic field using an endodontic needle. Group 5: IONP with magnetic field using ultrasound, and Group 6: 17% ethylenediaminetetraacetic acid (EDTA). Field emission scan electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) were utilized to determine cleaning root canal surfaces, opening dentinal tubules, removing the smear layer, and the percentage dispersion of ions on the root canal wall. The nonparametric tests of the Kruskal-Wallis, Mann-Whitney, and parametric test of One-Way ANOVA and Tuckey posthoc tests were used to compare irrigation protocols.

Results

Compared to the other groups, the agitation of irrigant IONP using a combination of a magnetic field and an ultrasound device proved to be the most effective. Additionally, the agitation of irrigant IONP using only an ultrasound device was more effective than using only normal saline with an ultrasound device. Iron ions have low percentages, perfect dispersions, and minimal precipitation in the apical section of the root canal wall.

Conclusion

Compared to the control group, the utilization of IONP irrigant agitation with a magnetic field did not affect dentinal structure while enhancing the cleaning of the canal surface, opening dentin tubules, and achieving a uniform distribution of iron ions with minimal precipitation. These findings may hold promise as a tool for endodontic treatment while preserving tooth structure.

Introduction

Endodontic infection is primarily caused by bacteria, which is considered an essential etiological factor for both initial and recurrent infection [1]. The bacterial cells’ attachment to the surface using a self-manufactured extracellular polymeric substance (EPS) [2, 3], leads to the formation of a biofilm of multicellular microbial communities that may include one or more species. These biofilms are recognized as significant virulence factors, exhibiting resistance levels up to 1500 times greater than planktonic cells [4, 5]. The entire removal of these microbes during treatment not only affects the successful treatment but also prevents the recolonization of microbes within the treated root canal system [6].

The movement of bacteria within the tubules is associated with canal infections [7], and it can penetrate through the tubules at a distance (300–1500 μm). Unfortunately, the conventional protocol of the root canal irrigant cannot approach this depth into the dentinal tubules [8], because of the anatomic complexities [1]. As a result, bacteria and their byproduct may persist around dentinal tubules even after conventional endodontic treatment [9].

Furthermore, research by Vera et al. (2012) investigated the mechanical cleaning and disinfection of root canals, revealing that microorganisms might inevitably persist within the canal even after treatment [10]. Paqué et al. (2010) showed that the areas of the flattened, oval, or C-shaped canals may stay untouched by instruments, especially at the wide canal diameter with varying cross-Sect. [11].

The agitation of irrigant inside the root canal system can be performed manually [12] or automatically [13]. Conventional irrigation techniques using sonic or ultrasonic activation, which involve transverse oscillation, are an inefficient method because of multiple touch points between the root canal walls and the file, especially at a narrow apical area [14] and cannot clean the root canal system efficiently [15]. Since the development of new technology in mechanical instrumentation and cleaning, still not all the root canal walls are cleaned because of the disparity between the complexities of the canal anatomy and instrument design [16].

Nanotechnology is the manufacture of structures at a scale of 100 nm or smaller, a near-atomic scale, to form new materials, structures, and devices [17]. Magnetic nanoparticles (MNPs) are a type of nanoparticles used in different fields of technology, such as medical therapeutics of drug carriers [18], and utilized in various field of dentistry as in endodontic root canal irrigant associated with peroxidase to improved antibacterial activity on root canal wall [19], prevention and treatment of dental caries through enhancement of antibacterial activity to word dental plaque biofilms [20], improved dentin’s adhesion of bonding agent without changing adhesive properties [21], and modified root canal sealer under the process of a magnetic field to management deeply penetrate of sealer with enhanced periapical healing [22].

In nanomedicine, the primary application involves the application of an external magnetic field to guide nanoparticles toward the target area, particularly employing superparamagnetic iron oxide nanoparticles (SPIONs) coated with organic or inorganic materials for drug delivery [23, 24]. The magnetite (Fe₃O₄) is better than natural iron oxide (black iron oxide) in spinel structure and displays the highest magnetism compared with other phases of IONP [25].

The tooth structure may be affected throughout exposure to irrigant solutions, potentially altering the integrity of the mechanical and chemical properties of natural enamel and dentin. Successful endodontic treatment depends on the use of irrigant solutions that do not alter the properties of the tooth structure [26].

This research aims to develop a new endodontic irrigant containing superparamagnetic iron oxide nanoparticles (SPIONs) to enhance root canal cleaning without the need for extensive canal shaping instruments, using an external magnetic field for guidance of the irrigant toward the target area and agitate the irrigant inside the root canal system. This novel approach showed the potential to bypass traditional instrumentation methods and prevent the loss of root structure when superparamagnetic iron oxide nanoparticles (SPIONs) and a magnetic field are employed, and can be considered a promising strategy to enhance the cleaning efficiency of root canal systems.

This study aimed to determine the optimum effect of iron oxide nanomagnet particles (IONPs) in cleaning the surface of the root canal and open dentin tubules, and analyzing the dispersion of iron ions with measurement concentration on the dentinal walls.

The null hypothesis was that iron oxide nanomagnet particles (IONP) irrigant agitation with a magnetic field would not enhance root canal cleaning and be effective in dentin structure.

Materials and methods

Sample collection

The G*Power program version 3.1.9.7 software measured the sample size calculation by selecting the variance analysis (ANOVA) test utilizing data from a previously conducted pilot study. The effect size (f) for the present study was 0.5200615, with an alpha (α) level of 0.05 (5%), and a beta (β) level of power was 0.80; the predicted sample size was a total of 54 samples. Hence, a total of nine specimens per group were needed. The sample size was increased to 60 by adding one root specimen per group. Thus, ten roots were used per group. The teeth were intact, non-carious, vital human maxillary first molars with extensive periodontitis that were collected from the mixed population at well-known dental centers for the therapeutic case, and informed consent was obtained from all participants whose teeth were extracted for periodontal therapy and used in this study. We clarified that the extracted teeth were used after the extraction, then stored in a 0.2% thymol solution for decontamination, not exceeding one month [27]. This experimental study was executed according to the ethical principles of the World Medical Association Declaration of Helsinki (version 2008). The Scientific Committee of the College of Dentistry-University of Baghdad (No. 1024 on 30/1/2025) has approved the collection of the teeth extracted for different purposes. Informed consent was obtained from all participants whose teeth were extracted for periodontal therapy and used in this study.

Samples selection

The magnifying lens was employed to inspect and exclude any teeth with anomalies, carious lesions, cracks, or open root apex [28]. Buccal and proximal radiographs were utilized to confirm the existence of a single straight palatal canal with a closed apex. To eliminate any variability in access preparation, palatal roots of the teeth were sectioned perpendicular to the longitudinal axis of the roots using 0.3 diamond discs No.913 (Komet, Germany) mounted on a straight handpiece at a low-speed (1500 rpm) (NSK, Japan) with a continuous flow of tap water. Subsequently, the root specimens were standardized to 12 mm from the apex to the coronal edge and fixed longitudinally in clear acrylic molds using additional silicon (Zermak, Italy) to facilitate handling during the instrumentation process.

Sample preparation

To achieve standardized procedures throughout the study, a single operator performed all the experiments to minimize variables during specimen preparation. The barbed broach was used to remove pulpal tissue, and a stainless-steel K-file size 10 (Dentsply, Maillefer, Switzerland) was inserted into the root canal until the tip was seen just exiting at the apical foramen, observing under a magnifying lens. The critical working length was obtained by subtracting 1 mm from the length. All the roots were instrumented with the conventional stainless-steel K-files sizes from size 15 to size 20, except the control group. The file was rotated clockwise in the root canal with slight pressure; then debris was removed by pulling the file slightly outward with clockwise rotations, each root canal was irrigated with 2 mL of normal saline between successive instruments by an endodontic needle had a double-sided access gauge 30 inserted at 3 mm short of working length [29]. The instruments were regularly cleaned to remove debris from the flutes. Each specimen requiring enlargement of more than file size 20 (Dentsply, Maillefer, Switzerland) was rejected and replaced by another one, excepted in control group the root specimens were standardized in length to be 12 mm from the apex to the coronal edge with no instrumentation or irrigation treatment A double-sided diamond disc, attached to a straight handpiece with water cooling, was used to create two longitudinal grooves on both the buccal and lingual sides (without deeply reaching the canal). This step aimed to aid in splitting the teeth into two segments with a chisel, following the groove’s path. The specimens were subsequently placed in phosphate-buffered saline (PBS) (Sigma, USA). The tooth samples were then randomly assigned to six experimental groups using the Excel program.

Generation of the magnetic field to agitation of iron oxide nanoparticles

A magnetic field was generated in this study by (Fig. 1):

Fig. 1.

Schematic diagram of magnetic field device

First permanent magnet: Super magnet neodymium 35, round-shaped, and diameter 18 mm (K&J Magnetics Inc., USA: Neodymium 35). The magnetic field strength remains constant, with 1000 gauss in the peripheral zone and 750 gauss in the central zone, and it does not lose its magnetic property when initiating magnetism. The magnet is positioned 10 mm from the palatal side of the root.

Second electromagnet: It consisted of a coil of wire wrapped around the iron core (self-made). When an electrical current is applied to this device, a magnetic field is generated, and then a magnet is created. The magnetic field strength can be adjusted using a self-made device that controls the electric current from a direct current (DC) power supply of 30 V. The device allows changes in the polarity and frequency (on-off cycles option, 10 times per second). The magnetic field strength in this study is 1300 gauss in the peripheral zone and 900 gauss in the central zone, which is stronger than the permanent magnet to ensure the agitation of iron oxide nanoparticles (IONP) within the root canal system. The electromagnet is located 10 mm from the buccal side of the root. The field strength between the two magnets is 450 gauss. A gaussmeter device calculated and identified the value of the magnetic field strength in the Scientific Research Authority, Ministry of Higher Education and Scientific Research, Baghdad, Iraq.

Preparation of irrigation solution

A solution consisting of 100 mg of the iron oxide nanoparticles (Fe₃O₄) size 25–50 nm (Us research nanomaterials Inc., Huston, USA) of dried powder (weighed using an electronic weight scale) (Radwag, Poland) was mixed with 10 mL of deionized water (10 g of IONPs powder in one litre of deionized water whereas the concentration of the iron oxide nanoparticles solution was 1%) according to the pilot study, bacteriological test, and cytotoxicity test, and then using ultrasonic mixing device at twenty minutes to obtain a clear colloidal dispersion [30].

Sample grouping

Group 1(protocol 1)

Control.

Group 2 (protocol 2)

Irrigation with ultrasound with no nanomagnet particles: Agitation of irrigant 50 mL of normal saline using continuous irrigation of an ultrasound device (Weedpecker U600, China) for 5 min.

Group 3 (protocol 3)

Agitation of irrigant 50 mL of IONP using continuous irrigation of an ultrasound device for 5 min.

Group 4 (protocol 4)

Agitation of irrigant 50 mL of IONP using a magnetic field with endodontic needle double side vented, gauge 30 (Hunterline, China) for 5 min. The syringe was attached to an electrically programmable syringe pump to release the irrigant at a flow rate of 10 mL /min.

Group 5 (protocol 5)

Agitation of irrigant 50 mL of IONP using a magnetic field with continuous irrigation of an ultrasound device for 5 min.

Group 6 (protocol 6)

EDTA 17% solution was introduced into the root canal through a needle gauge 30 for one minute.

The stainless-steel instrument E 62 used in continuous irrigation of the ultrasound device has a file diameter of 0.3 mm, taper 0%, and a working part length of 16 mm (Weedpecker U600, China). The tip of the file is held 2 mm shorter than the working length in the centre of the channel and moved 2–3 mm up and down. The file was set at power 50% as per the manufacturer’s instructions.

The roots were finally irrigated with 50 mL of normal saline through ultrasound devices for 5 min in each treatment was performed with IONP or EDTA 17%.

Utilize field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) analysis

Tooth specimens were isolated from clear acrylic molds, and two longitudinal grooves were opened by using a chisel and mallet. One half was prepared for SEM evaluation, and the second was for a microhardness test. The halves of the roots were washed with phosphate-buffered saline (PBS), then fixated by immersing in a solution containing 4% Glutaraldehyde in 0.1 mol/L sodium cacodylate buffer (BDH, England) (pH 7.4) at 4 °C overnight. Then, dehydrated in a step sequence of alcohol (Honeywell, Germany) (30, 50, and 70%) at 10 min, (90, and 100%) at 20 min, followed by immersion in hexamethyldisilazane (Merk, Germany) for 5 min, and air-drying [31, 32]. The halving of the root was mounted on aluminum stubs, sputter-coated with gold, and analyzed using field emission scanning electron microscopy (FE-SEM) (InspectTM F50) [33–36]. Each root was divided into three regions: coronal, middle, and apical, with one point selected from the center of the canal in each region for examination under magnifications 2500 X [31].

The Hulsmann scoring with a 5-score index was used to determine the optimum effect of iron oxide nanomagnet particles (IONP) cleaning the root canal surface, opening dentinal tubules, and removing the smear layer in each specimen Sects. [33, 37]:

Score 1

No smear layer; dentinal tubules are uncovered.

Score 2

Small quantity of smear layer; some dentinal tubules are covered.

Score 3

Uniform distribution of smear layer; only a few dentinal tubules are uncovered.

Score 4

A large quantity of uniform smear covers the entire root canal wall.

Score 5

Lack of uniformity and heavy smear layer.

The scoring was confirmed by a second examiner who was unaware of the treatment methods or experimental irrigants used. The examiner’s calibration scoring of the smear layer removal through the kappa test to assess interrater reliability value shows a substantial agreement level at the coronal section (measurement 0.679) and a near-perfect level of agreement at the middle and apical sections (measurement values 0.805 and 0.800, respectively).

The energy dispersive X-ray spectroscopy (EDS) (Thermo Fisher Scientific, Nederland) was used to determine the concentrations of iron (Fe) elements and measure the effect of magnetism on the dispersive Fe ions in the root canal walls of each section of the groups. The halving of the root was mounted on aluminum stubs and sputter-coated with gold, and then each root was divided into three regions: coronal, middle, and apical, with one point selected from the center of the canal in each area for examination [38, 39].

Statistical analysis

Data were analyzed using SPSS 26. The Shapiro-Wilks test checked the data’s normality. Nonparametric Kruskal Wallis and Mann Whitney test compared scores of groups at coronal, middle, and apical sections in each group. Parametric test of One-Way ANOVA and Tuckey posthoc tests were used to compare between continuous data. Statistical significance was set at p < 0.05.

Results

Assessment of root canal surface debridement and open dentin tubules by FESEM

The result of comparing the amount of smear layer of all protocols with group 1 (control) (Fig. 2), group 2 (agitation of irrigant normal saline using an ultrasound device) showed a higher mean rank of smear layer score (Fig. 3) than group 3 (agitation of irrigant IONP using ultrasound device) (Fig. 4), group 4 (agitation of irrigant IONP using a magnetic field with endodontic needle) (Fig. 5) showed the higher mean rank of smear layer score than group 5 (agitation of irrigant IONP using a magnetic field with ultrasound device) (Fig. 6), group 6 (EDTA 17%) showed the higher mean rank of smear layer score especially in middle and apical section (Fig. 7) than group 5 (agitation of irrigant IONP using a magnetic field with ultrasound device).

Fig. 2.

FESEM of canal wall in (protocol 1), A) coronal, B) middle, and C) apical sections

Fig. 3.

FESEM of canal wall in (protocol 2), A) coronal, B) middle, and C) apical sections

Fig. 4.

FESEM of canal wall in (protocol 3), A) coronal, B) middle, and C) apical sections

Fig. 5.

FESEM of canal wall in (protocol 4), A) coronal, B) middle, and C) apical sections

Fig. 6.

FESEM of canal wall in (protocol 5), A) coronal, B) middle, and C) apical sections

Fig. 7.

FESEM of canal wall in (protocol 6), A) coronal, B) middle, and C) apical sections

In all study groups, there were significant differences in the mean rank between groups in coronal, middle, and apical sections, as shown in Table 1.

Table 1.

Descriptive data of smear layer removal scoring between groups after the use of different protocols

Section	Group	N	Median	Mean rank	Minimum	Maximum	p-value*
Coronal	G1	10	5.00	56.20a	4	5	< 0.001
	G2	10	4.00	52.80a	4	5
	G3	10	2.50	30.05b	2	4
	G4	10	2.00	24.70b	2	3
	G5	10	2.00	19.15b	1	4
	G6	10	1.00	11.10c	1	2
Middle	G1	10	5.00	55.10a	4	5	< 0.001
	G2	10	4.00	46.25a	3	5
	G3	10	3.00	27.70b	2	4
	G4	10	3.50	36.80ab	2	5
	G5	10	1.00	7.45c	1	2
	G6	10	2.00	21.70b	2	3
Apical	G1	10	5.00	57.00a	5	5	< 0.001
	G2	10	5.00	57.002a	5	5
	G3	10	3.50	23.00c	3	4
	G4	10	4.00	31.50b	4	4
	G5	10	1.00	10.65d	1	4
	G6	10	5.00	46.80ab	4	5

*Kruskal Wallis test. Same superscript small letters indicate no significant differences, while different letters indicate significant difference between relevant groups in each section (Mann Whitney U test p < 0.05)

When comparing the amount of smear layer, group 5 (agitation of irrigant IONP using a magnetic field with ultrasound device) showed the lowest mean ranks of smear layer score in the middle and apical section, while showing higher mean ranks in the coronal section. In contrast, group 4 (agitation of irrigant IONP using a magnetic field with an endodontic needle) showed the lowest mean ranks of smear layer score in the coronal section and higher mean ranks in the middle and apical sections. Group 6 (EDTA 17%) showed a lower mean rank of smear layer score in the coronal section while a higher mean rank in the apical section (Fig. 7). There was a significant difference in the mean rank of smear layer scores between coronal, middle and apical section in groups 2,4 and 6 (p < 0.05). The most effective irrigation protocol was observed in group 5 (agitation of irrigant IONP using a magnetic field with an ultrasound device). This method significantly lowers the amount of smear layer, particularly in the middle and apical sections.

Assessment of the concentrations of iron (Fe) elements and measurement of the effect of magnet in dispersive Fe ions on the root canal wall by energy dispersive X-ray (EDS)

The data followed a normal distribution. A one-way ANOVA and Tukey post hoc tests were used to compare the groups and sections. There were significant differences in the iron element weight% level between groups at coronal, middle, and apical sections, with a p-value < 0.05. There was a minimum precipitation of ions in group 3 (agitation of irrigant IONP using an ultrasound device) at the apical section compared to the middle and coronal sections, followed by group 5 (agitation of irrigant IONP using a magnetic field with an ultrasound device) there was a minimum precipitation in the middle section (Fig. 8) compared to the coronal and apical sections, and followed by group 4 (agitation of irrigant IONP using a magnetic field with an endodontic needle) there was a minimum precipitation in the apical section compared to the middle and coronal sections. This is presented in Table 2.

Fig. 8.

IONPs showed in the EDS A) spectrum of elements and B) the maps of dispersive of iron (Fe) ions on the root canal wall

Table 2.

Descriptive data of iron weight between groups at coronal, middle, and apical sections

Section	Group	N	Mean	Std. Deviation	Minimum	Maximum	*p-value
Coronal	G1	10	0.00a	0.00	0.00	0.00	< 0.001
	G2	10	0.00a	0.00	0.00	0.00
	G3	10	1.32b	0.54	0.60	2.00
	G4	10	1.62b	0.92	0.30	2.90
	G5	10	1.19b	0.38	0.60	1.70
	G6	10	0.00a	0.00	0.00	0.00
Middle	G1	10	0.00a	0.00	0.00	0.00	< 0.001
	G2	10	0.00a	0.00	0.00	0.00
	G3	10	1.13b	0.36	0.50	1.60
	G4	10	1.37b	0.90	0.40	2.90
	G5	10	0.85b	0.35	0.30	1.30
	G6	10	0.00a	0.00	0.00	0.00
Apical	G1	10	0.00a	0.00	0.00	0.00	< 0.001
	G2	10	0.00a	0.00	0.00	0.00
	G3	10	0.55ab	0.07	0.50	0.70
	G4	10	1.24b	0.89	0.30	2.70
	G5	10	1.27b	0.86	0.20	3.20
	G6	10	0.00a	0.00	0.00	0.00

* One-way ANOVA test. Same superscript small letters indicate no significant differences, while different letters indicate significant difference between relevant groups in each section (Tukey post hoc p < 0.05)

Discussion

The smear layer is a thin film, approximately 1–2 μm thickness, that forms on the root canal wall [40]. It comprises remnants of vital or necrotic pulp tissue, dentin particles, bacterial biofilm, and irrigants that block the opening of the dentinal tubule [41]. This layer must be removed because it serves as a microbial reservoir [42], limit the penetration action of the disinfecting agent, and separation between filling materials and the canal wall, ultimately compromising the sealing ability of the root canal [43].

The success of endodontic treatment has an impact relation with the irrigation protocol, as no single irrigant solution can meet al.l the required criteria [44]. The irrigation protocols should also remove the smear layer and debris from all root canal system [45].

In this study utilized various irrigant solutions, including normal saline, IONP, and 17% EDTA. To optimize the cleaning of the root canal system while conserving the maximum tooth structure, six groups were activated using different activation techniques, including ultrasonic oscillation [46], and using an external magnetic field [24], either alone or in combination with ultrasonic oscillation.

In this investigation, the passive ultrasound protocol of irrigation is more effective than syringe needle irrigation in eliminating the remnants of pulpal tissue, bacterial biofilm, and smear layer [46]. This finding aligns with another study that recommends using nanoparticles with an ultrasound device in biomedical applications [47]. Another study investigated the direct effect when using a sterile normal saline irrigant to remove planktonic bacteria from the root canal [48]. In this study, normal saline irrigant with ultrasound was less effective than other nanoparticle irrigants. The irrigant was delivered through the hollow, smooth wire to the root canal [49]. The apical region of root canals showed less debris and smear layer than the coronal region because of the high density of acoustic streaming at the apical region. Cameron, in 1983, found that a 3-minute and 5-minute period of passive ultrasound irrigation was most effective in removing the smear layer, whilst a 1-minute irrigation was ineffective [50]. These results are coincident with the study as irrigation at 5-minute periods. In contrast to another study, it was found that ultrasonic irrigation was unable to remove the smear layer [51], but in this study, it was found that applying nano irrigant with file size 15 of an ultrasound device can remove the smear layer with a conservative tooth structure. Lumley et al. 1992 recommended a high volume of microstreaming only with a file size of 15, especially when the tips of the file vibrate freely in an irrigant solution with maximizing the removal of debris [52]. Other study found that the benefits of using the ultrasonic irrigation technique only for the final irrigation after finished of hand instrumentation [46].

In this study, the agitation of IONP irrigant demonstrated a lower mean rank of smear layer score compared to normal saline when using an ultrasound device. This finding aligns with the results of Murugesan et al., who showed a higher smear layer score after using normal saline irrigant activated by ultrasound [53].

In this study, EDTA 17% was used as an irrigant, which binds to calcium ions in dentin and dissolves the inorganic part of the smear layer [54]. However, complete removal of the smear layer is not achievable [55], with its most effective action occurring during the first minutes of application [56, 57]. Also, the research showed catastrophic damage to peritubular dentin when the time of application remains between 1 and 10 min [58]. Another study reported that applying 10 mL of EDTA 17% solution for one minute effectively removed the smear layer from the canal walls. In contrast, prolonged exposure to dentin increases the degree of demineralization [58–60]. Additionally, in this study, it was observed that the apical section of the canals showed inferior cleaning efficiency compared to the middle and coronal sections. The reason for the incomplete removal may be due to the failure of irrigants to reach the apical section, and the coincidence with other studies [61, 62]. Sodium hypochlorite was not used in this study because it was decided to examine the effectiveness of magnetic agitation with IONP as a physical treatment with other variables. Sodium hypochlorite will be studied in further research.

There is no published data about the efficiency of the magnet activation system with IONP in cleaning the root canal, opening dentinal tubules, and removing the smear layer in the coronal, middle, and apical sections of straight root canals. Two methods have been used to evaluate this effect of IONP: one uses extracted natural teeth, and the other simulates root canals. Otherwise, simulated root canals allow a uniform root canal diameter and length, but are not used in this study because dentin structures may not be identical. All the investigations of root canal treatment techniques, cleaning and shaping, irrigation protocol, and irrigant solution have focused on the cleaning ability of each system as the main objective, but have excluded the core goal of treatment, which involves the conservative structure of the root canal and removes the probability of instrument fracture.

Hence, new strategies are essential, as achieving optimal root canal cleaning can significantly enhance the success of treatment outcomes. To conform to this goal, we propose using iron oxide nanoparticles (IONPs) in combination with an external magnetic field and ultrasound activation as an innovative approach to more effectively open dentinal tubules compared to existing methods.

According to preliminary studies, the minimum inhibitory concentration of the IONP is 7.8125 mg/mL, and the minimum bactericidal concentration is 15.625 mg/mL (unpublished data). Hence, the concentration used in this study was 10 mg/mL to allow continuous flow of IONP irrigant through the application devices.

The use of ultrasonic activation with a magnetic field better results in the penetration depth of the irrigant. This is in agreement with another study that found hydrodynamic irrigation improved the penetration depth of irrigant solution into the root canal wall dentine [63]. The application of an external magnetic field to guide nanoparticles toward the target area is the major application in nanomedicine, with superparamagnetic iron oxide nanoparticles in drug delivery [18, 24].

All irrigation activation protocols using continuous ultrasonics agitated IONP, compared with normal saline. These protocols demonstrated that utilizing IONP as an irrigant, combined with magnet activation and ultrasonic techniques, yielded the most effective results for removing debris and the smear layer throughout the canal system.

This study showed that activating the IONP irrigant was significantly more effective in removing the smear layer, regardless of the agitation method. This was evident when comparing the results with the use of saline solution alone, which did not exhibit any effect on cleaning the root canal and removing the smear layer.

Conclusion

Compared to the control group, the use of IONP irrigant agitation with a magnetic field did not affect dentinal structure while enhancing root structure compared to EDTA irrigation, cleaning the surface of the canal, open dentin tubules, uniform distributions of Fe ions with minimum precipitation, which may indicate only a negligible extrusion beyond the root canal and can be regarded as effective options for endodontic treatment while preserving the tooth structure.

Abbreviations

SPIONs

Superparamagnetic iron oxide nanoparticles solution

IONP

Iron oxide nanomagnet particles

Fe

Iron

FE-SEM

Field emission scan electron microscopy

EDS

Energy-dispersive X-ray spectroscopy

EPS

Extracellular polymeric substance

PBS

Phosphate-buffered saline

mol/L

Moles per liter

ml

/min Milliliters per minute

MNPs

Magnetic nanoparticles

nm

Nanometer

µm

Micrometer

mm

Millimeter

DC

Direct current

Fe₃O₄

Iron oxide

V

Voltage

Author contributions

Ehsaan S. Al-Mustwfi: Conceptualization, Data curation, Methodology, Investigation, Project administration, Resources, Funding Acquisition, Software, Writing – Original Draft, Writing – Review & Editing.Hussain F. Al-Huwaizi: Supervision, Validation, Visualization, Formal analysis, Funding Acquisition, Writing – Review & Editing. All authors read and approved the final manuscript, wrote the main manuscript text, and prepared Figs. 1, 2, 3, 4, 5, 6, 7 and 8.

Funding

This project did not receive any funding.

Data availability

Data is provided within the manuscript information files.

Declarations

Ethics approval and consent to participate

This experimental study was executed according to the ethical principles of the World Medical Association Declaration of Helsinki (version 2008). The Scientific Committee of the College of Dentistry-University of Baghdad (No. 1024 on 30/1/2025) has approved the collection of the teeth extracted for different purposes. Informed consent was obtained from all participants whose teeth were extracted for periodontal therapy and used in this study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.