Single Cone Obturation versus Cold Lateral Compaction Techniques with Bioceramic and Resin Sealers: Quality of Obturation and Push-Out Bond Strength

Objectives This study compared the obturation quality and push-out bond strength of single cone obturation (SCO) and cold lateral compaction (CLC) with AH-Plus and Sure Seal Root (SSR). Materials and Methods This in vitro experimental study was conducted on 88 single-rootedsingle-canal teeth with straight roots that were randomly divided into four groups (n = 22). All teeth were decoronated and underwent cleaning and shaping. Obturation was performed with AH-Plus and SCO technique in group 1 (SAH), AH-Plus and CLC technique in group 2 (LAH), SSR and SCO technique in group 3 (SS), and SSR and CLC technique in group 4 (LS). The roots were then sectioned into 3-mm thick slices and underwent digital photography at x25 magnification to assess the quality of obturation in the coronal, middle, and apical thirds by Image J software. The PBS was measured by a universal testing machine. The mode of failure was also determined under a stereomicroscope. Results The PBS was significantly higher in the LSS group than LAH and SAH groups, and also in the SSS group than the SAH group in all sections. The PBS in the LSS group was significantly higher than SSS in the coronal and middle thirds. Voids were significantly lower in LAH than in the SAH group in all sections. In LSS, voids in the coronal third were significantly lower than in LAH. In the middle third, voids in SSS were significantly lower than in SAH. The groups had no significant difference in the mode of failure (P > 0.05). The mean percentage of gutta-percha in the use of AH-Plus sealer was significantly higher than SSR (P < 0.05). The mean percentage of gutta-percha in the coronal third was lower than that in the middle and apical thirds (P < 0.05). Conclusion SSR showed higher PBS and less voids than AH-Plus. High PBS of the CLC/SSR group showed that CLC should still be preferred to SCO, and in the case of using SCO, SSR should be preferred to AH-Plus.


Introduction
Root canal therapy is performed to resolve the root canal infection and prevent/eliminate periapical infection [1][2][3]. Tree-dimensional sealing of debrided root canals is a critical step to prevent the reentry of microorganisms and their toxins into the root canal system and their extrusion into the periapical tissue, which can lead to treatment failure [3][4][5]. Endodontic sealers are essential for sealing the entire root canal length, apical foramen, root canal irregularities, and the gap between the root canal wall and the core root flling material [6]. According to Chandra [7], an ideal sealer should have properties such as excellent sealing ability after setting, adequate dimensional stability, optimal adhesion to the canal walls, and favorable biocompatibility [7]. At present, diferent types of sealers are available in the market including glass ionomer-based, zinc-oxide, and resin sealers. However, there is still a need for a sealer with more favorable properties [8]. Accordingly, bioceramic sealers were recently introduced [9].
Calcium silicate-based sealers are presented in the following two forms: (I) one-component sealers (ready-to-use), which are available in a premixed syringe with calibrated intracanal tips and utilize external water supply to set, and (II) two-component sealers with internal water supply [10].
Recently, a premixed injectable calcium silicate-based sealer known as Sure Seal Root (SSR) BC Sealer was introduced into the market. As stated by the manufacturer, it utilizes moisture to initiate and complete its setting reactions. After setting, a chemical bonding occurs with a void-free interface between the gutta-percha, sealer, and radicular dentin. Te physicochemical properties of this sealer have been the topic of considerable attention. Tis sealer has an alkaline pH, optimal chemical stability, and high biocompatibility [12][13][14].
Diferent obturation techniques are available including the use of thermoplastic gutta-percha, cold lateral compaction (CLC), vertical condensation, and single-cone obturation (SCO) techniques. Te CLC technique has a high level of safety, is cost-efective, and has shown favorable clinical results. It is the standard root canal obturation technique [3]. However, it has drawbacks such as a high level of difculty, risk of void formation, and risk of vertical root fracture due to the application of wedging forces by instruments such as spreaders. Also, the CLC technique may have a suboptimal outcome due to incomplete obturation of curved canals. In the CLC technique, the correct use of a spreader may help in gaining more space for the insertion of accessory gutta-percha points [15].
Te SCO technique is a subtype of the CLC technique in which one gutta-percha point is prepared with a taper compatible with the fnal shape and taper of the canal and is inserted into the canal, allowing complete obturation without any accessory points [15]. Te SCO technique is often associated with a good outcome in the round, narrow, and regular root canals. However, the outcome may not be satisfactory in root canals with irregular shapes. Tis technique does not require compaction and is popular due to its simplicity and fast process. Tis technique requires a higher amount of sealer than the compaction and condensation techniques; thus, its outcome depends more on the properties of the sealer [15].
Optimal adhesion and adaptation of root-flling material to the canal walls play a fundamental role in the provision of the expected hermetic seal in endodontic treatment. Terefore, the push-out test is commonly used to quantitatively assess this adhesion [16].
Tis study aimed to compare the quality of root canal obturation and the push-out bond strength (PBS) of SCO and CLC techniques by using AH-Plus resin sealer and SSR bioceramic sealer.

Materials and Methods
Tis in vitro experimental study was conducted on 88 singlerooted, single-canal teeth with straight root canals as confrmed on two periapical radiographs taken at two diferent angles perpendicular to each other. Te teeth had been extracted for purposes not related to this study (such as poor periodontal prognosis or orthodontic treatment). Te study was approved by the ethics committee of Ardabil University of Medical Sciences (IR.ARUMS.REC.1398.212).
Te teeth were stored in 0.05% sodium chloramine solution at room temperature since this solution is commonly used for disinfection and storage of extracted teeth in vitro [17,18].
Te inclusion criteria were (I) root length of 10 to 15 mm, (II) absence of severe curvature in the roots, absence of oval-shaped orifce, and absence of internal/external root resorption, and (III) initial fle size not larger than #20.
Te sample size was calculated to be 22 in each group (a total of 88 in 4 groups) according to a study by Krug et al. [19], assuming alpha � 0.05, beta � 0.2, and study power of 80%.
Te teeth were inspected at x20 magnifcation and those with root cracks were excluded. Te teeth were decoronated 1 mm above their cementoenamel junction (CEJ) by a diamond disc at low speed (Isomet, Buchler, Lake Bluf, USA) under water spray. At this step, teeth that did not meet the eligibility criteria were excluded and replaced. Te working length was determined by using the largest fle that reached the apex (Mani, Tochigi, Japan); 1 mm was subtracted from its length to determine the working length. At this step, teeth with an initial fle size >20 were excluded and replaced. Te teeth were then instrumented by using the gold-standard ProTaper rotary system according to the standard protocol of the manufacturer up to #F5. After using each fle, the root canals were rinsed with 5.25% sodium hypochlorite with a side-vented needle. Next, the root canals were rinsed with 2 mL of 17% EDTA, followed by 2 mL of 5.25% sodium hypochlorite, and fnally, with 4 mL of saline. Te root canals were dried with paper points (PT Dent, USA) and were randomly divided into four groups (n � 22). Te teeth were excluded and replaced in case of the occurrence of any procedural error.

Group 1 (SS).
A #F5 gutta-percha point was inserted into the canal to the working length. SSR (Sure Dent Corp., Gyeonggi-do, Korea) was then delivered into the coronal third of the root canal using an intracanal tip. Also, the apical third of gutta-percha was dipped in the sealer and gently inserted into the canal. Excess gutta-percha was cut at the CEJ, and the coronal part of gutta-percha was condensed with gentle pressure using an endodontic plugger.

Group 2 (SAH).
A #F5 gutta-percha was inserted into the canal to the working length. AH-Plus sealer (Dentsply DE Trey, Konstanz, Germany) was then delivered into the coronal third of the root canal using an intracanal tip. Also, the apical third of gutta-percha was dipped in the sealer and gently inserted into the canal. Excess gutta-percha was cut at the CEJ, and the coronal part of gutta-percha was condensed with gentle pressure using an endodontic plugger.

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International Journal of Dentistry

Group 3 (LS).
A #50 gutta-percha with 0.02 taper was inserted into the canal to the working length. Sure Seal Root was then delivered into the coronal third of the root canal using an intracanal tip. Also, the apical third of gutta-percha was dipped in the sealer and gently inserted into the canal. Next, a #30 spreader (Mani, Tochigi, Japan) was inserted into the canal adjacent to the master cone at a 0-2 mm distance from the working length. Accessory gutta-percha points (#25/0.02) were placed in the space created by the spreader immediately after its removal. Excess gutta-percha was cut at the CEJ, and the coronal part of gutta-percha was condensed with gentle pressure using an endodontic plugger.

Group 4 (LAH).
A #50 gutta-percha with 0.02 taper was inserted into the canal to the working length. AH-Plus was then delivered into the coronal third of the root canal using an intracanal tip. Also, the apical third of gutta-percha was dipped in the sealer and gently inserted into the canal. Next, a #30 spreader (Mani, Tochigi, Japan) was inserted into the canal adjacent to the master cone at a 0-2 mm distance from the working length. Accessory gutta-percha points (#25/ 0.02) were placed in the space created by the spreader immediately after its removal. Excess gutta-percha was cut at the CEJ, and the coronal part of gutta-percha was condensed with gentle pressure using an endodontic plugger. All phases of cleaning and obturation of root canals were performed by the same operator. A radiograph was then obtained from all specimens to ensure the optimal quality of root canal flling. Teeth with voids or other detectable procedural errors on radiographs were excluded and replaced. Te teeth were then incubated at 37°C and 100% humidity for 14 days to allow the complete setting of sealers.

Quality of Obturation with Gutta-Percha and Sealer.
Te teeth were fxed with cyanoacrylate glue and horizontally sectioned in the apical, middle, and coronal thirds to obtain slices with a maximum thickness of 3 mm [20]. A low-speed diamond disc (Isomet, Buchler, Lake Buf, USA) was used for this purpose under water spray. Te slices were then inspected under a stereomicroscope (Expert DN) at x25 magnifcation and were digitally photographed. Te teeth with oval-shaped root canals or isthmuses were excluded and replaced. Te areas were flled with gutta-percha and sealer, and the voids were quantifed by Image J software (National Institutes of Health, public domain) and reported as a percentage. Tis process was repeated by another operator, and the obtained values were recorded. Te level of agreement between the two observations was found to be 1, indicating excellent agreement.

PBS Test.
Each specimen was subjected to apico-coronal force application along the longitudinal axis of the tooth. Te load was applied by cylindrical rods with 0.45, 0.6, and 0.9 mm diameters in a universal testing machine (Hounsfeld Test Equipment, model: H5K-S, England). For each specimen, a rod that covered approximately 90% of the surface of root-flling material was selected. Te load was applied at a crosshead speed of 0.5 mm/minute until fracture. Te maximum load at fracture was recorded in Newtons (N). Te PBS in Newtons was converted to megapascals (MPa) by dividing the load (N) by the cross-sectional area of the entire surface subjected to load application, which was calculated using the following formula: where a1 is the canal diameter in the coronal part of the slice, a2 is the canal diameter in the apical part of the slice, and h is the slice thickness. Te specimens were then inspected at x20 magnifcation to determine the mode of failure, which was categorized as cohesive (fracture within the flling material), adhesive (fracture at the interface of dentinal wall and flling material), and mixed (a combination of adhesive and cohesive).

Statistical
Analysis. Data were analyzed using SPSS version 22. Te Kolmogorov-Smirnov test was used to analyze the normality of data distribution. An independent t-test was used to compare the percentage of canals flled with a sealer, and the Mann-Whitney U test was used to compare the PBS and voids among the groups. Intergrouptwo-way and three-way ANOVA were applied to compare the percentage of canals flled with gutta-percha, and the Chi-square test was used to analyze the correlation between the failure mode and the study group. Te level of signifcance was set at 0.05. Table 1 presents the mean and standard deviation of PBS, percentage of gutta-percha, percentage of voids, and percentage of sealer in the study groups.

PBS.
Te Kolmogorov-Smirnov test showed the nonnormal distribution of PBS data (P < 0.001). Tus, the Kruskal-Wallis test was applied to compare the PBS of the study groups, which showed a signifcant diference (P < 0.001). Pairwise comparisons by the Mann-Whitney U test (Table 2) showed that the mean PBS in the LSS group was signifcantly higher than LAH and SAH groups in the coronal, middle, and apical thirds. Te mean PBS in the SSS group was signifcantly higher than the SAH group in the coronal, middle, and apical thirds (P < 0.05). Te mean PBS in the SSS group was signifcantly higher than the SAH group (P < 0.05). Te mean PBS in the LSS group was signifcantly higher than the SSS group in the coronal and middle thirds (P < 0.05). Te mean PBS in the SSS group was signifcantly higher than the LAH group in the middle and apical thirds (P < 0.05). No other signifcant diferences were noted.

Percentage of Voids.
Te Kolmogorov-Smirnov test showed a non-normal distribution of the percentage of voids (P < 0.001). Tus, the groups were compared in this regard International Journal of Dentistry 3 by the Kruskal-Wallis test, which showed no signifcant diference among the study groups in the percentage of voids (P > 0.05).

Percentage of Gutta-Percha.
Te Kolmogorov-Smirnov test showed normal distribution of the percentage of gutta-percha data (P > 0.05). Tus, three-way ANOVA was applied to compare the groups in this regard and assess the efect of the technique of obturation, type of sealer, and area of the root (coronal, middle, or apical) on the percentage of gutta-percha. Te results showed no signifcant diference in the mean percentage of guttapercha between the two obturation techniques (P > 0.05). A signifcant diference existed in the mean percentage of gutta-percha between the two sealers, and the mean percentage of gutta-percha in AH Plus was signifcantly higher than SSR (P < 0.001). Also, a signifcant diference existed in the mean percentage of gutta-percha among the coronal, middle, and apical thirds (P < 0.05). Pairwise comparisons showed that the mean percentage of guttapercha in the coronal third was signifcantly lower than in the middle and apical thirds (P < 0.05). No other significant diferences were found in this regard (P > 0.05). Independent samples t-test was used to analyze the efect of the obturation technique on the mean percentage of guttapercha based on the two sealer types. Te results are presented in Table 3. Table 4 presents the mean sealer percentage in the study groups. Tree-way ANOVA was applied to analyze the efect of the obturation technique on the mean sealer percentage based on the type of sealer and the area of the root (coronal, middle, and apical third). Te results showed signifcant efects of type of sealer (P < 0.001), area of the root (P < 0.001), interaction of obturation technique and sealer type (P � 0.001), and the interaction of obturation technique, sealer type, and area of   Table 5.

Mode of Failure.
Group and mode of failure were not signifcantly correlated, and the frequency of modes of failure was not signifcantly diferent among the groups (P > 0.05).

Discussion
A hermetic apical seal is imperative for a successful endodontic treatment to prevent the leakage of fuids and materials from the periradicular tissue into the root canal system and vice versa [21,22]. According to Ramezanali et al. [23], many endodontic problems are due to incomplete root canal sealing. Gutta-percha, in combination with sealer, serves as the gold standard for root canal obturation due to optimal biocompatibility, no toxicity or allergic reactions, and easy retrieval from the root canal system. However, it has shortcomings such as the inability to increase the root strength since it cannot bond to dentin and the incomplete flling of the root canal space [24]. Evidence shows that PBS cannot directly predict the clinical success of treatments.
However, it provides valuable information regarding the comparison of sealers and diferent obturation techniques [3,25]. Tus, the PBS was measured in this study to assess the bond strength of root-flling materials to root canal walls and the efcacy of the CLC obturation technique. Te CLC technique was selected in this study since it is currently the most commonly used obturation technique [3,25]. Te SCO technique is also suggested by the manufacturers of the new generation of bioceramic sealers [3,25]. Te mean PBS in the LSS group was signifcantly higher than LAH and SAH groups in the coronal, middle, and apical thirds. Te mean PBS in the SSS group was signifcantly higher than the SAH group in the coronal, middle, and apical thirds (P < 0.05). Te mean PBS in the SSS group was signifcantly higher than the SAH group (P < 0.05). Te mean PBS in the LSS group was signifcantly higher than the SSS group in the coronal and middle thirds (P < 0.05). Te mean PBS in the SSS group was signifcantly higher than the LAH group in the middle and apical thirds (P < 0.05). In line with the present results, O'Brien et al. [18] 2020 compared the PBS of AH-Plus and CeraSeal bioceramic sealer and reported that the mean PBS in the bioceramic sealer group was higher than that in the AH-Plus group. To explain the results, it should be stated that Sure Seal Root bioceramic sealer forms chemical bonds to dentin through the synthesis of hydroxyapatite during its setting reactions, and thus, higher bond strength is achieved in the use of this sealer. Also, Sure Seal Root is easily infused into the dentinal tubules and creates a hermetic seal [16]. Te percentage of root canal flling was also evaluated in this study. Gutta-percha is the most commonly used rootflling material. Sealers are used for better adaptation of gutta-percha to the root canal walls. Since the dimensional stability of gutta-percha is higher than that of sealer, the percentage of gutta-percha should be as high as possible, and the percentage of sealer should be lower in an ideal obturation [26][27][28]. Accordingly, the present study quantifed the percentage of gutta-percha, sealer, and voids in diferent sections. Te current results showed no signifcant diference in the mean percentage of gutta-percha between the two obturation techniques, which is similar to the past studies [29][30][31].
In the present study, the mean percentage of sealer in the AH-Plus group was signifcantly lower than SSR (P < 0.001). Tis fnding can be due to the fact that bioceramic sealers undergo a little expansion rather than shrinkage [32]. Also, the mean percentage of gutta-percha was signifcantly different among the coronal, middle, and apical thirds, and it was lower in the coronal third than the middle and apical thirds. Te discrepancy between the canal shape and fle shape increases in the coronal third due to greater root canal irregularities in this area, which can be one reason for the   International Journal of Dentistry higher percentage of residual sealer in the coronal third [33]. Finally, based on the present results, the percentage of voids did not difer signifcantly among the groups. Both obturation techniques and also both sealers produced voids, which is in accordance with the fndings of Celikten et al. [34], who suggested that voids are mainly correlated with the root canal anatomy rather than the root canal flling material or technique.

. Strengths
Tis study compared two common obturation techniques qualitatively and quantitatively.

Limitations
Tis study had an in vitro design. Tus, a complete simulation of the clinical setting was not possible. Also, when sectioning the teeth, smearing of the flling material on the sectioned surface may occur despite water cooling. Unnoticed smearing might have infuenced the accurate measurement of small voids. Moreover, when using sliced sections, only a 2-dimensional assessment of void areas can be performed. Tus, to overcome these shortcomings, additional use of nondestructive scans of the teeth would be benefcial.

Conclusion
Sure Seal Root has better physical, chemical, and sealing properties compared to AH-Plus. Te high push-out bond strength of lateral compaction/Sure Seal group showed that cold lateral compaction should still be preferred to singlecone obturation. In the case of using the single cone technique, SSR is superior to AH Plus.

Data Availability
Te data used to support the fndings of this study were supplied by the corresponding author under license and data will be available on request. Requests for access to these data should be made to the corresponding author.

Conflicts of Interest
Te authors declare that they have no conficts of interest.