Radiopacity of calcium silicate-based root canal sealers: a comparative analysis

Authors

Abstract

Aim This study aimed to compare the radiopacity of newly developed calcium silicate-based root canal sealers using digital radiography.
Materials and Methods
The tested materials included AH Plus, AH Plus Bioceramic, NeoSealer Flo, Bioserra, MTA Cem S, and gutta-percha cones. Each material was placed in circular molds (10 ± 1 mm in diameter, 1 ± 0.1 mm in height). Samples were positioned on a phosphor plate alongside a 14-step aluminum step wedge. Digital radiographs were obtained at 60 kVp, 7 mA, 0.25 s exposure time, and a 30 cm focal spot-object distance. ImageJ software was used to measure mean gray values, and radiopacity was expressed in millimeters of equivalent aluminum (mm Al). Data were analyzed using Kruskal-Wallis and Bonferroni post hoc tests.
Results AH Plus showed the highest radiopacity (11.43 mm Al), followed by AH Plus Bioceramic (10.06 mm Al), gutta-percha (7.22 mm Al), Bioserra (6.52 mm Al), NeoSealer Flo (4.22 mm Al), and MTA Cem S (3.27 mm Al). AH Plus and AH Plus Bioceramic had significantly higher radiopacity than Bioserra, NeoSealer Flo, and MTA Cem S (p < 0.05). The radiopacity of MTA Cem S and NeoSealer Flo was significantly lower than that of other sealers and gutta-percha.
Discussion MTA Cem S showed the lowest radiopacity among the tested materials, except for NeoSealer Flo. In clinical practice, insufficient radiopacity may impair the detection of voids or inadequate fillings, which could compromise treatment success. Therefore, the radiographic properties of bioceramic sealers should be carefully evaluated during material selection.

Keywords

Introduction

Biomechanical preparation and chemical irrigation during root canal treatment play crucial roles in eliminating bacteria from the root canal system. Preventing re-infection of root canals and controlling endodontic infection is achieved through successful root canal filling [1]. Traditionally, gutta-percha is the primary root canal obturation material. However, due to its inability to adapt perfectly to root canals, it is often used alongside an endodontic sealer, which fills the gaps that gutta- percha cannot cover, including accessory canals and multiple foramina [2].
AH Plus (Dentsply DeTrey, Konstanz, Germany) is a gold- standard epoxy resin root canal sealer in the endodontic filling [3]. As time has progressed, a newer generation of root canal sealers, known as bioceramic root canal sealers, has been developed and made available. These modern sealers are bioactive materials with excellent sealing ability, antibacterial properties, resistance to dissolution in tissue fluids, and strong adhesion to dentin. Additionally, new calcium silicate sealers support the single cone technique, which may enhance the use of sealers and change root canal filling methods [4].
AH Plus Bioceramic (Dentsply Sirona, Switzerland) is a hydraulic bioceramic sealer. It sets quickly and offers high resistance to washout. Additionally, its low solubility and minimal film thickness enhance its ability to adapt to the root canal, as stated by the manufacturer. NeoSelar Flo (Avalon Biomed, Houston, TX, USA) is another innovative bioactive bioceramic sealer [5]. The material is biocompatible, non-cytotoxic, and non-genotoxic. It initially exhibits high pH in vitro antimicrobial properties, according to the manufacturer. Most recently, the new hydraulic calcium silicate-based bioceramic sealers Bioserra and MTA Cem S have been introduced [5]. Bioserra (Meta Biomed, Chungcheongbuk-do, Korea) is a flowable sealer that sets slowly within the root canal by absorbing moisture. MTA Cem S (Nexobio, Chungcheongbuk-do, Korea) is premixed and ready to use in a single syringe, demonstrating excellent biocompatibility as stated by the manufacturer.
Endodontic sealers must possess adequate radiopacity, along with physicochemical and antibacterial properties, to be distinguishable from surrounding tissues and materials on radiographic images. This radiopacity is essential for evaluating the quality of obturation in post-treatment radiographs [6]. While manufacturers assert that bioceramic sealers have high radiopacity, independent research on these materials remains limited, particularly for MTA Cem S and Bioserra. This study aimed to compare the radiopacity of bioceramic sealers with AH Plus and gutta-percha using digital radiography. The null hypotheses for this study are: The radiopacities of the tested materials meet ISO standards, and the materials exhibit no statistically significant difference in radiopacity.

Materials and Methods

The study employed gutta-percha cones and five root canal sealers: four premixed calcium silicate-based (AH Plus Bioceramic, NeoSealer Flo, Bioserra, and MTA Cem S) and one epoxy resin-based (AH Plus).
Sample Preparation
Circular polytetrafluoroethylene molds (10 ± 1 mm inner diameter, 1 ± 0.1 mm height) were used to prepare samples. Root canal sealers were prepared per the manufacturer’s instructions, and heated gutta-percha cones and sealers were placed into the molds. For each material, five samples were prepared using circular molds covered with cellophane-taped glass to ensure a smooth surface. Samples were incubated at 37°C and 100% humidity until set, then demolded and measured for thickness using a digital caliper (SHAN Electronic Digital Caliper).
Digital Radiography
Each material was placed on a phosphor plate alongside a 14- step aluminum step wedge, with each step measuring 1 mm in thickness. This setup assessed the test materials’ radiopacity. The intraoral X-ray unit (Kodak 2100) was operated at 60 kVp, 7 mA, and 0.25 seconds exposure time. The X-ray unit was positioned 30 cm away from the test materials at a 90° angle to the surface of the phosphor plate. For each individual sample, a set of five radiographic images was acquired (n = 25).
Evaluation of Digital Radiography
Digital images were imported into a computer using ImageJ 1.52 software (National Institutes of Health, Bethesda, MD, USA). Radiopacity was measured at five points on each radiograph and penetrometer step to ensure consistency and minimize sealer-related variability. When selecting measurement areas, regions free of air bubbles within the material were chosen. Measurements were conducted by a blinded observer (T.K.). The radiographic densities of the specimens were determined using the toolbox in the same software, and the mean gray values were converted to millimeters of aluminum (mm Al) [7]. for recording. The calculation of averages was performed using a dataset comprised of twenty-five distinct and independent measurements.
Statistical Analysis
Statistical analysis was performed using IBM SPSS 25 software. The assumption of normal distribution was assessed using the Shapiro-Wilk test. The Kruskal-Wallis test was utilized to examine differences among three or more independent groups that did not have a normal distribution. Post Hoc Bonferroni tests were conducted to identify specific groups that contributed to any observed differences. Statistical significance was set at p<0.05.
Ethical Approval
This study was conducted in a laboratory environment solely on dental materials; thus, it does not require ethical committee approval or patient consent.

Results

The compositions, manufacturers, and batch numbers of the materials used in the study are detailed in Table 1. The radiographic image of the evaluated root canal sealers is shown in Figure 1, and Table 2 provides the mean radiopacity values and standard deviations (mm Al equivalent) for each material. All tested root canal sealers and gutta-percha met the minimum radiopacity values established by ISO 6876/2001. AH Plus displayed the highest radiopacity (11.43 mm Al), followed by AH Plus Bioceramic (10.06 mm Al), gutta-percha cones (7.22 mm Al), Bioserra (6.52 mm Al), NeoSealer Flo (4.22 mm Al), and MTA Cem S (3.27 mm Al), in descending order. Both AH Plus and AH Plus Bioceramic sealers demonstrated significantly higher radiopacity than Bioserra, MTA Cem S, and NeoSealer Flo, with a significance level of p<0.05. MTA Cem S had the lowest radiopacity value, which was statistically significantly different from all the sealers except NeoSealer Flo (p < 0.05). Furthermore, NeoSealer Flo and MTA Cem S had significantly lower radiopacity compared to gutta-percha. Conversely, the radiopacity of AH Plus was significantly higher than that of gutta-percha (p < 0.05). AH Plus Bioceramic exhibited higher radiopacity than gutta-percha, while Bioserra had lower radiopacity, though this difference was not statistically significant (p > 0.05)

Discussion

The radiopacity of root canal sealers is an important factor that plays a crucial role in the radiographic evaluation of the quality of the obturation [6]. High radiopacity can be beneficial for clinicians assessing the outcomes of endodontic treatments. However, excessive radiopacity can create artifacts in advanced imaging techniques, such as cone beam computed tomography, potentially leading to incorrect diagnoses [8, 9]. Although ISO standards state that the radiopacity of these materials should be at least equivalent to that exhibited by a 3 mm thickness of aluminum, the absence of an upper limit leads to a wide variation in the radiopacity values of different sealers, which can influence the accuracy of radiographic assessments and the interpretation of treatment outcomes [10]. Therefore, clinicians need to consider the radiopacity values of the filling materials they choose to use. Upon reviewing the literature, no studies were found investigating the radiopacity of MTA Cem S and Bioserra. Therefore, in our study, we compared the radiopacities of various bioceramic sealers with widely used AH Plus and gutta-percha. According to the findings of our study, all root canal sealers tested exhibited radiopacity above 3 mm Al, meeting ISO standards. Therefore, the hypothesis that the radiopacities of the tested materials met the minimum value specified in ISO standards was accepted.
Several factors can affect a material’s radiopacity values, including imaging systems, exposure parameters, object-source distance, exposure time, film speed, and the measurement method employed [6, 11]. Therefore, our study serves as a benchmark for the comparative analysis of the tested bioceramic root canal sealers using a consistent digital imaging method and standardized exposure parameters. Additionally, the thickness of the material significantly influences radiopacity values [12]. International standards recommend using standard disks fabricated in molds to mitigate this variation. In our study, we utilized standardized circular molds made of polytetrafluoroethylene with a thickness of 1 mm to compare the radiopacities of the materials.
AH Plus is widely recognized in endodontics as a high-quality epoxy resin-based root canal sealer. Previous studies have consistently reported that AH Plus exhibits greater radiopacity compared to various calcium silicate-based bioceramic sealers [3, 13, 14]. In agreement with these findings, the present study also demonstrated that AH Plus had the highest radiopacity value among the tested materials. Furthermore, no statistically significant difference was observed between the radiopacity of AH Plus (11.43 mm Al) and AH Plus Bioceramic (10.06 mm Al). This result is consistent with other studies evaluating the radiopacity of calcium silicate-based sealers, which similarly reported comparable values for AH Plus and AH Plus Bioceramic [3, 15].
However, our findings contrast with those of LC de Souza et al., who reported that AH Plus Bioceramic exhibited significantly lower radiopacity than AH Plus [16]. Likewise, the results differ from those of Kwak et al., who found that AH Plus Bioceramic demonstrated higher radiopacity than AH Plus [14]. These discrepancies may be attributed to variations in radiographic methodologies across studies, particularly differences in exposure parameters such as exposure time, kilovoltage peak (kVp), and milliampere-seconds (mAs).
The radiopacity of a material is largely dependent on the atomic number of the elements that make up the material [10]. Root canal sealers contain radiopacifying agents such as bismuth oxide, zirconium oxide, and tantalum oxide [5]. Bismuth, with an atomic number of 83, is generally considered more radiopaque than tantalum (atomic number 73) and zirconium (atomic number 40). However, the radiopacity of a material cannot be attributed solely to the presence of radiopacifying agents. Studies have demonstrated that other factors -including molecular structure, physical density, and the method of radiopacifier synthesis and incorporation- also play a significant role in determining the radiopacity of dental materials [10, 17]. For example, MTA Fillapex, a bioceramic-based root canal sealer containing bismuth oxide as a radiopacifier, has been reported to exhibit low radiopacity values of 3.01 mm Al and 3.48 mm Al, compared to other sealers [18, 19]. Notably, no previous studies have investigated the radiopacity of MTA Cem S. In our study, MTA Cem S, despite containing bismuth oxide, showed the lowest radiopacity value among the tested sealers at 3.27 mm Al. This difference was statistically significant when compared to all other materials, except NeoSealer Flo. These findings further support the notion that radiopacity is influenced by multiple material characteristics and not solely by the type or presence of a radiopacifier. Therefore, the null hypothesis, suggesting no statistically significant difference in radiopacity among the tested materials, was rejected.
Only a limited number of studies have investigated the radiopacity of NeoSealer, with reported values ranging from 4.9 mm Al to 5.5 mm Al, and up to 10.79 mm Al [13, 19, 20]. In the present study, NeoSealer Flo, which contains tantalum oxide as a radiopacifier, exhibited a radiopacity value of 4.22 mm Al. This was significantly lower than that of AH Plus (11.43 mm Al) and AH Plus Bioceramic (10.06 mm Al), both of which contain zirconium oxide. Our findings are consistent with those of Zamparini et al., who reported that the radiopacity of NeoSealer (5.5 mm Al) was lower than that of AH Plus (11.5 mm Al) and AH Plus Bioceramic (8.6 mm Al) [13]. The compositional differences between the materials likely explain this discrepancy: AH Plus Bioceramic contains approximately 70% zirconium oxide by mass, whereas NeoSealer Flo contains only 40–50% tantalum pentoxide [13]. This difference in radiopacifier type and content appears to contribute to the significantly lower radiopacity observed in NeoSealer Flo. Numerous studies indicate that calcium silicate-based materials display varying radiopacity values, even when the same radiopacifying agents are employed [3, 13, 14]. Kwak et al. found that different root canal sealers containing zirconium oxide (EndoSequence BC Sealer, TotalFill BC Sealer, and Bio-C Sealer) showed lower radiopacity than AH Plus Bioceramic, attributed to AH Plus Bioceramic’s higher zirconium oxide content of about 70% [14]. In our study, when AH Plus Bioceramic and Bioserra, containing a similar radiopacifying agent (zirconium oxide), were compared, AH Plus Bioceramic (10.06 mmAl) showed higher radiopacity than Bioserra (6.52 mmAl). No information regarding the proportion of zirconium oxide in Bioserra was found in the literature. Therefore, we believe that the lower radiopacity of Bioserra may be related to its low zirconium oxide content. However, further studies are needed to confirm this.
A literature review revealed no studies comparing the radiopacity of gutta-percha with that of AH Plus Bioceramic, Bioserra, Neoselar Flo, and MTA Cem S. In our study, Neoselar Flo and MTA Cem S exhibited lower radiopacity than gutta- percha, while AH Plus Bioceramic and Bioserra showed similar radiopacity to gutta-percha. These findings align with previous reports indicating that AH Plus possesses higher radiopacity than gutta-percha [21, 22]. Gutta-percha cones typically contain radiopacifying agents such as barium sulfate and zinc oxide, which contribute to their radiopacity [22]. The differences observed in the radiopacity of the tested materials are likely attributable to variations in the type, concentration, and distribution of radiopacifying agents within their chemical compositions.
Ideally, root canal filling materials are expected to remain within the boundaries of the root canal system without extending beyond it [23]. Extrusion of root canal sealers beyond the apical region has been reported to slow down healing or lead to nerve damage [23, 24]. Therefore, the sealer used should be distinguishable from both gutta-percha and adjacent anatomical structures, contributing to the accurate analysis of treatment outcomes and the management of potential complications. According to Gambarini et al., the use of highly radiopaque filling materials in combination with gutta- percha may hinder the detection of imperfections within root canal obturations [12]. In this context, when evaluating the results of our study, it is predicted that the use of Neosealer Flo and MTA Cem S as root canal sealers (due to their lower radiopacity than gutta-percha) may provide clinicians with visual distinction advantages in clinical evaluation after root canal filling. Conversely, when AH Plus Bioceramic and Bioserra are used (due to their similar radiopacity to gutta-percha), it is assessed that it may be difficult to distinguish these materials from gutta-percha.

Limitations

A limitation of this study is its in vitro design. In clinical settings, factors such as soft tissue, bone, dentin, and the use of root canal sealer with gutta-percha can influence the radiographic density of root canal fillings, potentially altering radiopacity values [6]. Furthermore, the interaction of sealers with varying compositions and thicknesses, particularly when used in conjunction with gutta-percha, may impact the overall radiopacity observed in clinical imaging [12]. Therefore, evaluating radiopacity solely based on standardized disc specimens constitutes an additional limitation of the present study.

Conclusion

The findings of this study indicate that, despite variations in radiopacity among the tested root canal filling materials, all of them met or surpassed the minimum radiopacity criteria outlined in ISO 6876/2001. In addition, the radiopacity of Bioserra, NeoSealer Flo, MTA Cem S, and gutta-percha was lower than that of AH Plus and AH Plus Bioceramic. Notably, MTA Cem S demonstrated lower radiopacity than all the materials except for NeoSealer Flo. The findings suggest that radiopacity shows significant differences between materials in the selection of endodontic sealers and should be considered in terms of clinical imaging.

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