Penetration of Three Endodontic Sealers in Simulated Lateral Canals during the Lateral Condensation Technique: An In Vitro Study

Objective This study aimed to compare the penetration depths of AH Plus, BioRoot RCS, and GuttaFlow 2 into simulated lateral canals when used with the cold gutta-percha lateral compaction technique. Materials and Methods Twelve resin training blocks (4 canals perch each resin block) were used. Each primary artificial canal had two lateral canals (apical and coronal). The main canals were instrumented with WaveOne Gold and irrigated with distilled water. The resin blocks were divided into three groups (N = 4 each/16 artificial canals), according to the type of root canal sealer; Group I: AH Plus, Group II: BioRoot RCS, and Group III: GuttaFlow 2. All canals were obturated with the cold lateral condensation technique. The linear extension of each endodontic sealer into the apical and coronal lateral canals was measured using a digital stereomicroscope and measuring software. Data were statistically analyzed using a one-way analysis of variance. The percentages of filling of the lateral canals were calculated and statistically compared using the Mann–Whitney test. Results The experimental sealers exhibited variable penetration depths into the lateral canals. All sealers showed significantly better penetration ability into the apical lateral canals than the coronal lateral canals (P < 0.05). AH Plus (3.184 ± 0.012 mm/99.5%) and GuttaFlow 2 (3.176 ± 0.017 mm/99.25%) were significantly better than BioRoot RCS (3.096 ± 0.026 mm/96.75%) in filling the apical lateral canals (P < 0.05). BioRoot RCS was the best sealer to fill coronal lateral canals (3.322 ± 0.085 mm/83.05%). Conclusion During the lateral condensation technique, the filling of the lateral canals is affected by the type of root canal sealer and the location of the lateral canals All the sealers tested have a good ability to fill the apical lateral, while BioRoot RCS was effective in filling both the coronal and apical lateral canals.


Introduction
Infection of the root canal system is considered the main cause of periapical lesions [1]. Inadequately flled areas in a well-prepared root canal system can be a source of microbial growth, as 58% of treatment failures were reported to be due to insufcient obturation [2]. Terefore, a threedimensional flling of the canal space with an inert biocompatible material is required to prevent bacterial leakage and reinfection of the root canal system [3].
Total flling of the root canal system is a clinical challenge due to its inherent morphological complexities [4]. Te root canal system may be complicated by the presence of several ramifcations, such as lateral and accessory canals, which harbor some pulp tissues and microorganisms [5]. Te incidence of lateral canals is relatively high, ranging from 27.4 to 99% [6], and may be considered a cause of failure after endodontic treatment if they are not properly cleaned and sealed [7]. Tere is a strong correlation between infection inside root canals and the presence of apical periodontitis [7]. Furthermore, some studies have reported endodontic success after the obturation of lateral canals [8,9]. Consequently, root canal flling procedures should include the flling of the main root canal, as well as the lateral and accessory canals [10].
Despite the development of numerous obturation techniques, the cold lateral condensation technique is considered the most common obturation technique, as it is simple and does not require sophisticated equipment, and is easy to learn [11]. Additionally, several authors showed that the lateral condensation technique has a sealing ability similar to other newly developed obturation techniques [12].
Root canal sealers play an important role in the success of any obturation technique. Terefore, it is important to use a sealer with good sealing, antibacterial, and fow properties, as well as radiopacity, dimensional stability, and low cytotoxicity [13]. To this day, there is no product that combines all the ideal properties, which may explain the need for the continuous development of new endodontic sealers [14]. Currently, there are various types of contemporary endodontic sealers on the market, such as AH Plus (Dentsply De Trey GmbH, Konstanz, Germany), GuttaFlow 2 (Coltène/ Whaledent, Altstätten, Switzerland), and more recently the BioRoot RCS (Septodont, Saint-Maur-des-Fosses, France).
AH Plus (DeTrey Dentsply GmbH, Konstanz, Germany) is an epoxy resin-based endodontic sealer that exhibits excellent physical properties and bond strength with dentin, [13,15]. One of the advanced materials on the market is GuttaFlow (Coltène Whaledent, Altstatten, Switzerland), which is based on silicone-based sealer and gutta-percha powder. More recently, this product has been modifed, giving rise to GuttaFlow 2 which has good physicochemical properties, low cytotoxicity, and good adhesiveness to dentin [16][17][18].
Recently, bioceramic root canal sealers have been released on the market and became popular among endodontists due to their excellent physical and biological properties. Tese materials showed auspicious properties of radiopacity, fow, osteoconductivity, alkaline pH, low cytotoxicity and genotoxicity, and adequate antibacterial effectiveness [19]. BioRoot RCS (Septodont) is a type of bioceramic sealer composed of tricalcium silicate, zirconium oxide, and calcium chloride. It is indicated for permanent root canal flling in combination with gutta-percha cones and is suitable for use in single-cone or cold lateral condensation techniques [20].
Variable methods have been used to study the flling of lateral canals. Goldberg et al. [21] used natural human teeth after drilling simulated lateral canals and then examined the flling of the lateral canals radiographically. Venturi et al. [22] used the same previous method but examined the flling of lateral canals using the clearing technique. Dulac et al. [23] used resin blocks after drilling simulated lateral canals. Venturi et al. [24] used Termafl training resin blocks to study the penetration of root canal sealers into the lateral canals.
Currently, limited information on the penetration of BioRoot RCS and GuttaFlow 2 into lateral root canals is available when used with the lateral condensation technique. Terefore, the present study aimed to evaluate the ability of AH Plus, BioRoot RCS, and GuttaFlow 2 to fll artifcial lateral canals in two diferent locations, when the lateral condensation technique was used. Te null hypothesis tested was that there are no signifcant diferences between the penetration capacities of experimental sealers into artifcial lateral canals at diferent locations when used with the cold lateral condensation technique.

Materials and Methods
Te Research Ethics Committee of Ajman University, UAE under protocol number UGD-H-18-12-24-44, approved the present study.

Termafl Resin Training
Blocks. Termafl training blocks (Dentsply Maillefer) were used in the current study ( Figure 1). Each resin block had four primary canals of 18 mm in length and 25°curvature. Each main canal had two lateral canals located at 5 mm (apical lateral canal) and 11.5 mm (coronal lateral canal) from its apical end. Each lateral canal had three successive cylinders (inner, middle, and external) of diferent lengths and diameters. Te overall length of the apical lateral canals was 3.2 mm (inner length: 0.2 mm, middle length: 1 mm; coronal length: 2 mm), while the length of the coronal lateral canals was 4 mm (inner: 1 mm, middle: 1 mm; coronal: 2 mm). Te diameters of the internal, middle, and external cylinders in both lateral canals were 0.5, 0.7, and 1 mm, respectively. Te diameter of the coronal orifce of each primary canal, 3 mm from the surface of the resin block, was 1 mm and its apical end diameter was 0.3 mm with a 4% taper. Te dimensions of the main and lateral canals mentioned above were according to Venturi et al. [24] and were confrmed in the current study using a digital microscope and measurement software.

Samples Size
Calculation. An experimental design of repeated measures was performed. Sample size estimation was performed a priori using G * Power 3.1.9.6 (Universität Kiel, Kiel, Germany) [25], assuming that a standardized efect size of 0.7276 should be detected by repeated measures ANOVA at 95% power and with a two-tailed probability of alpha type error of 0.05. Finally, a sample size of 16 artifcial canals was selected for each group in the present study (4 resin blocks), resulting in a total of 16 artifcial canals with 32 artifcial lateral canals.

Canal Instrumentation.
Canal instrumentation procedures were performed under an endodontic microscope at 16x magnifcation (Carl Zeiss Microscopy, LLC). Te patency of all main and lateral canals was verifed using a #20 stainless steel K-fle (Dentsply, Maillefer). Te working length (WL) was established at 1 mm short of the standardized length of each main canal (WL � 17 mm). All canals were prepared with WaveOne Gold reciprocating endo fle size 45/0.05 (Dentsply, Maillefer Sirona) according to the manufacturer's instructions. EDTA gel (Glyde File Prep, Dentsply, Maillefer, Switzerland) was used as a lubricant during instrumentation procedures. Tree cutting cycles were used at three working lengths of 5.5 mm in length. After each cutting cycle, the fle was removed, and its futes were cleaned from any resin debris and inspected for any visible distortion or unwinding. Te root canals were irrigated with 5 ml of distilled water after each preparation cycle using a side-vented needle (Max-I-Probe, Dentsply). After the instrumentation was completed, the patency of the main and lateral canals was again verifed with a #20 K fle. According to previous studies, each WaveOne gold fle was used to prepare four canals and then discarded, to ensure its cutting efciency [26,27].

Samples Grouping.
After fnishing the preparation of all artifcial canals, the thermal fll training blocks (N � 12 resin block) were divided, according to the type of root canal sealers, into three groups of 4 resin blocks each (16 prepared canals/32 lateral canals) Group I: AH Plus, Group II: Bio-Root RCS, and Group III: GuttaFlow 2. Te composition of each experimental sealer is shown in Table 1.

Canal Obturation.
Before starting the obturation phase, each acrylic block was covered with a layer of heavy body impression material (ZetaPlus, 3M ESPE, Saint Paul, USA) to simulate the periodontium. Te prepared canals were dried with Wave One Gold paper points (large size). Te canals of the Bioroot RCS group were dampened using a moistened paper point to ensure the setting of this hydrophilic sealer. Te selected root canal sealer (AH Plus; Group I, BioRoot RCS; Group II; GuttaFlow 2; Group III) was mixed according to the manufacturer's instructions and applied to the prepared resin canal using a #30 Lentulo spiral rotated at 300 rpm and 3 mm shorter than the working length. Te tip of preselected master gutta-percha cone size 45/0.02 was lightly coated with sealers and slowly inserted into the canal until it reached the full working length. Lateral condensation was performed using a premeasured size C fnger spreader (D1 diameter 0.3 mm, 0.04 taper) (Dentsply, Maillefer) and standardized gutta-percha cones of size 25/ 0.02. Accessory cones were added and lateral condensation was continued until the spreader could not penetrate more than 3 mm from the surface of the acrylic block. Te excess gutta-percha was seared using a hot instrument and lightly vertically compacted. All obturated samples were stored at 37°C and 100% humidity in an incubator for one week to allow the sealers to be completely set.
All instrumentation and obturation procedures were done by the author who is a specialist in endodontics.

Measurement of Sealer Penetration into Lateral Canals.
All flled canals were inspected with a digital stereomicroscope (Leica EZ4W, Germany) at 12.5x magnifcation and photographed from the same aspect at the outer margin of the resin block to standardize the evaluation (Figure 2). Photographic images showing the root canal fllings in each specimen were imported into Image Tool software (ImageJ software, National Institutes of Health, Bethesda, USA). After calibrating the software, the length of sealer penetration into each lateral canal was measured in mm and also expressed as a percentage of linear extension (length of the flled portion of the lateral canal divided by its entire length). Two independent examiners, previously calibrated and blinded to the study, measured the sealer penetration into the artifcial lateral canals at two diferent time intervals according to the assessment criteria prescribed previously. International Journal of Dentistry

Results
Te level of interexaminer agreement was very high, attaining a kappa value of 0.92 [28]. Te means and standard deviations of the penetration depths of sealers in the lateral canals are presented in Table 2. Furthermore, the percentages of flling of the lateral canals with experimental sealers are presented in Table 3. All experimental sealers showed variable penetration depths into the apical and coronal lateral canals. When the penetration depths of the experimental sealers into the apical and coronal lateral canals were compared, the one-way ANOVA test showed highly signifcant diferences between the groups (P < 0.05  (Table 3), the apical lateral canals showed signifcantly higher percentages of sealer flling than the coronal lateral canals (P < 0.05).

Discussion
Te flling of the lateral canals is clinically important for any obturation technique to overcome the possible bacterial growth and reinfection of the root canal system [10,18]. Several studies have reported endodontic success after lateral canal flling; diferent flling techniques were proposed to achieve better obturation of these canals [11]. Terefore, the present study aimed to compare the penetration ability of three contemporary endodontic sealers into simulated lateral canals when used with the lateral condensation technique.
In the current study, ready-made training blocks were used, in which the dimensions of the main and lateral canals  are standardized. Terefore, the variations associated with the instrumentation and flling procedures of the main canals were also standardized [23]. Te only drawback of these training blocks is that the surface texture of the epoxy resin blocks is not similar to the natural tooth structure, which may afect the fow of the endodontic sealer. Additionally, the internal diameters of the simulated lateral canals (500, 700, and 1000 μm) used in this study were larger than the natural diameters of the natural lateral canals [22]. However, the flling of large lateral canals may indicate the ability of root canal sealers to fll narrow canals.
To reduce variability in instrumentation procedures, all simulated canals were prepared and obturated by one operator. To standardize the preparation size of the canals, WaveOne Gold fle size 45/0.05 was used to prepare the main canals, which have an initial size of 0.30 mm and a taper of 4%. During instrumentation, EDTA gel was used to decrease the friction between the fle and canals, and collect the resin debris to be easily removed during the irrigation. Irrigation was done with distilled water, as artifcial resin canals were used. Te terminal ends of the main and lateral canals were blocked with a rubber base impression material prior to flling the main canal according to the idea described by Almeida et al. [29]. Tis procedure allowed the sealer to be confned after it had fowed through the lateral canals in an attempt to simulate the role of the periodontal ligament.
Te combination of gutta-percha with a suitable endodontic sealer is usually used for root canal flling. Te flling of the lateral canals may be afected by the obturation technique [15] and the physical-chemical properties of the endodontic sealer [17]. Cold lateral condensation was selected in the current study, as it is still the technique most used clinically, as it is a relatively simple technique and it can achieve a good sealing ability that was similar to other obturation techniques [11,12]. In addition, the main goal of this study was to evaluate sealers and not flling techniques in terms of flling lateral canals.
Te quality of endodontic sealer plays an important role in the flling of the ramifcations and lateral canals. In the present study, three types of sealers were selected, AH Plus, BioRoot RCS, and GuttaFlow 2, based on their excellent physical properties and clinical performance [16]. Te selected root canal sealers were mixed according to the manufacturer's instructions and placed in the prepared canals using a Lentulo spiral. Guinesi et al. stated that the use of the Lentulo spiral is a crucial method to place sealer within the root canals when the single-cone obturation technique is used [30].
An adequate fow of endodontic sealers is a fundamental physical property that allows them to fll small spaces, accessory canals, and spaces between the master and accessory cones [16]. Karabucak et al. concluded that the fow of flling material into the lateral canals is a function of the viscoelastic properties of the flling material rather than the mechanical properties of the delivery systems [31].
Te pseudoplastic and thixotropic properties of endodontic sealers afect their fowability by decreasing their viscosity when subjected to pressure or stress [16]. According to Hubbe et al., the thixotropic material transforms its internal structure under constant shear stress, which promotes the alteration of the fow speed, accounting for the abrupt fow, after a certain time [32]. Pseudoplastic material exhibits the same changes as a result of increasing the rate of shear stress [16]. Tixotropic materials have a higher viscosity when moved at a slow speed and a lower viscosity when moved at a higher speed [16].
GuttaFlow 2 and AH Plus are thixotropic materials for which their viscosity decreases and their fow increases under constant shear stress [33]. On the other hand, a bioceramic-based sealer is pseudoplastic material that shows the same behavior as thixotropic materials but with an increasing rate of shear stress [16]. Some authors found that bioceramic sealers have higher fowability compared to GuttaFlow and AH Plus [16]. Also, it has been confrmed that GuttaFlow 2 has a better fow than AH Plus [33]. Regarding BioRoot RCS, some authors found that it has a larger flm thickness and lower fow than AH Plus [34].
In the literature, there are few studies on the penetration capacity of BioRoot RCS and GuttaFlow 2 into lateral canals when used with the lateral condensation technique. Te present results showed that the flling of the lateral canals was afected by the type of endodontic sealers and the location of the lateral canals. Terefore, the null hypothesis was rejected.
Te results of the present study indicated that the lateral apical canals had high percentages of flling with all experimental sealers. Tis fnding is clinically signifcant because it is well-known that there is a greater percentage of lateral canals in the apical third of the root. Tis can be clarifed because all sealers have thixotropic and pseudoplastic properties [16,33]. Under constant or increased shear stresses during lateral compaction procedures, the viscosity of the sealers decreases, and their fow increases [16,33]. However, the penetration ability BioRoot RCS in the apical lateral canals (3.096 mm/96.75%) was slightly lower than that of AH Plus (3.184 mm/99.5%) and GuttaFlow 2 (3.176 mm/99.25%). Te cause of this may be due to its high viscosity when subjected to more shear stresses that relatively decrease its fow [16]. Moreover, some authors found that the BioRoot RCS has more flm thickness and lower fow than that of the AH Plus [34]. Te present results are in confict with Venturi et al. [22] and Goldberg et al. [4] who concluded that the lateral canals localized in the apical third of the root were more difcult to fll. Te causes of this  [35]. Te results of this study indicated that all tested sealers showed lower percentages of penetration into the coronal lateral canals than into the apical lateral canals. During the cold lateral compaction of the gutta-percha cones, the generated shear stress is not continuous but instant. Tis force is dissipated both by decreasing the pressure on the walls with increasing canal taper and by losing the mass of the cement, resulting in reduced fow and incomplete flling of the lateral canals [36]. Despite the low fow of BioRoot RCS [34], it showed better penetration ability into coronal lateral canals (3.32 mm/83%) than AH Plus (2.84 mm/71%) and GuttaFlow 2 (2.69 mm/67.28%). Tis may be due to the location of these lateral canals in the straight portion of the canal and the pushing of the sealer coronally to penetrate the lateral canal. Additionally, the existing results are somewhat in agreement with the results of Teixeira et al. who showed that the GuttaFlow 2 sealer had less penetration ability into the apical lateral canals (secondary canals) when used with the cold lateral compaction technique [37]. However, the authors showed that AH Plus had better penetration ability into apical lateral canals. Te reason for this incongruity was the diference in methodology. Tose authors manually prepared the root canals of natural teeth using a step-back technique, and the two coronal and apical artifcial lateral canals of smaller diameters were mechanically prepared within the roots.
Te presented results cannot be straightforwardly applied clinically, because the penetration of flling materials could be hindered clinically by some factors, such as the diameter of the lateral canals and the lack of patency due to the presence of remnants of the pulp tissue, or dentin debris [7]. However, the results can be used as an indicator of which root canal sealer has a better ability to penetrate the lateral canals when used with cold lateral condensation techniques. Te proper irrigation of the root canal system is the only way to clean the lateral and accessory canals and allow sealers to fll them [7]. Kanumuru et al. in their study found that negative pressure irrigation (EndoVac system) and passive ultrasonic irrigation (PUI) promoted better cleaning of the main and simulated lateral canals than the conventional manual irrigation technique [38].
In addition to the penetration ability of root canal sealers into the lateral canals, other important characteristics must be respected during the selection of root canal sealers such as tissue biocompatibility, antimicrobial property, and sealing ability. More studies may be required to study the penetration ability of the investigated sealers into the lateral canals when used with other obturation techniques such as the matched-tapersingle-cone technique.
Based on the results of the current study, the penetration ability of root canal sealers in lateral canals is afected by the type of root canal sealer and the location of the lateral canals. All sealers used with the lateral condensation technique showed signifcantly better flling for the apical lateral canals than the coronal lateral canals. AH plus and GuttaFlow 2 showed better penetration into the apical lateral canals than BioRoot RCS. BioRoot RCS showed a higher penetration ability into the coronal lateral canals than AH Plus and GuttaFlow 2. BioRoot RCS could be a suitable sealer to be used with cold lateral compaction, which can adequately fll the apical and coronal lateral canals simultaneously.

Conclusions
Based on the results of the current study, the penetration ability of root canal sealers in lateral canals is afected by the type of root canal sealer and the location of the lateral canals. All tested sealers had a better ability to fll the apical lateral canals than the coronal lateral canals. BioRoot RCS showed the best penetration ability into both apical and coronal lateral canals and could be considered a suitable sealer to be used with cold lateral compaction.

Signifcant of the Study.
Filling the lateral canals after proper cleaning with an efcient irrigation protocol is clinically important. Te lateral canals can be flled with endodontic sealers during the lateral compaction technique. Te type of sealer plays a critical role in flling the lateral and accessory canals. Most of the lateral canals are confned in the apical area of the roots., but some of them may be found coronally. All sealers tested showed good penetration in the apically positioned lateral canals when used with the lateral compaction technique. However, BioRoot RCS was the only sealer that could fll the coronal and apical lateral canals. Meanwhile, this sealer has excellent sealability and biocompatibility as well as antibacterial properties.

Abbreviations
ANOVA: Analysis of variance WL: Working length EDTA: Ethylenediamine tetra-acetic acid.

Data Availability
Te data used to support the fndings of this study will be available from Dr. Mohamed Elsayed at this e-mail: elsayednada@yahoo.com for the researchers who meet the criteria for accessing this data. Te data can be requested after the publication of this article. However, requests for the data, (6/12 months) after the publication of this article, will be considered by the corresponding authors.

Conflicts of Interest
Te author declares that there are no conficts of interest regarding the publication of this article.
International Journal of Dentistry 7