A comparative analysis of adhesion abilities between AH Plus^® Bioceramic, Ceraseal^® and AH Plus^® on root canal dentine surfaces

Abstract

Introduction:

The adhesion of sealers to dentin is a vital aspect of endodontic success. Epoxy resin-based sealers such as AH Plus^® are considered the gold standard for their strong mechanical adhesion, but they lack bioactivity. Calcium silicate-based sealers such as AH Plus^® Bioceramic and Ceraseal^® offer bioactive potential. This study compares the push-out bond strength and failure modes of three root canal sealers: AH Plus^® Bioceramic, Ceraseal^®, and AH Plus^®.

Materials and Methods:

Thirty mandibular premolars were prepared and divided into three groups (n = 10): Group I (AH Plus^® Bioceramic), Group II (Ceraseal^®), and Group III (AH Plus^®). Push-out bond strength was measured in MPa at apical and medial root segments using a universal testing machine. Failure modes were evaluated using a digital microscope at ×30 and ×100 magnification.

Results:

AH Plus^® exhibited the highest mean bond strength (14.65 ± 2.42 MPa), followed by Ceraseal^®. AH Plus^® Bioceramic showed the lowest bond strength (2.31 ± 0.21 MPa). Failure modes in Group I were predominantly mixed, whereas Groups II and III had balanced cohesive and mixed failures.

Conclusions:

While all sealers adhered well to dentin, AH Plus^® Bioceramic demonstrated significantly lower bond strength compared to AH Plus^® and Ceraseal^®.

INTRODUCTION

Ideally, endodontic sealing material should demonstrate strong adhesion to both dentin and gutta-percha, forming a monoblock system that enhances the resistance of dentin within the root canal.[1,2] Among root canal sealers, AH Plus^® (Dentsply Maillefer, USA) is considered the gold standard due to its superior physical properties. It achieves robust adhesion to dentin through the mechanical interlocking of resin in the dentin tubules and covalent bonding between epoxy resin rings and the amine groups in dentin collagen. However, it cannot form bonds that mimic tooth structure or apatite.[3,4,5]

In contrast, bioceramic sealers represent a significant advancement compared to their predecessors and exhibit superior bioactive properties.[6] They can form apatite-like bonds along the sealer and dentin surfaces through electrostatic interactions and ionic and hydrogen bonding involving calcium, phosphate, and silanol, known as the Mineral Infiltration Zone (MIZ).

Adhesion is further enhanced by the formation of tag-like structures on dentin tubules and collagen components, which are degraded by the alkaline action of sealer hydration byproducts.[7] AH Plus^® Bioceramic (Dentsply Maillefer, USA) is the newest addition to the category of tricalcium silicate-based sealers, but limited research has been conducted on its properties. Conversely, Ceraseal^® (Meta Biomed Co., Cheongju, Korea) is an established calcium silicate-based sealer composed of zirconium dioxide, tricalcium silicate, dicalcium silicate, tricalcium aluminate, and polyethylene glycol. Recent research found that Ceraseal^® exhibited faster setting times, higher calcium ion release, and a superior increase in pH compared to AH Plus^® Bioceramic and AH Plus^®. However, the flowability of Ceraseal^® and AH Plus^® was greater than that of AH Plus^® Bioceramic.[8,9,10]

The push-out bond strength test is commonly used to evaluate the adhesive strength of sealers to dentin.[11,12] A recent study by Shieh et al. confirmed that the push-out bond strength of AH Plus^® surpassed that of AH Plus^® Bioceramic and Endosequence^® BC Sealer.[11] Researchers also analyze the failure modes to determine the quality of sealer adhesion to dentin, categorizing failures as adhesive, cohesive, or mixed.[13,14] Notably, there is a lack of research on the bond strength of AH Plus^® Bioceramic and how it compares to similar sealers like Ceraseal^® and the gold standard, AH Plus^®. This study aims to investigate and compare the differences in bond strength between calcium silicate and epoxy resin-based sealers on the dentin surface of root canals.

MATERIALS AND METHODS

The sample comprised thirty mandibular premolars selected according to the specific inclusion and exclusion criteria. The inclusion criteria included caries-free teeth that were approximately 21 mm in length, possessed a single and straight root, had a single root canal, and had not undergone any previous root canal treatment, pin restoration, or placement of artificial crowns. Meanwhile, the exclusion criteria involved teeth exhibiting root resorption, cracks, curved roots, or any anatomical abnormalities.

Postextraction teeth were immersed in phosphate-buffered saline at the room temperature. The crown portion of each tooth was excised using a diamond disk, leaving a root length of 15 mm. Root canal preparation was conducted using the crown-down technique with ProTaper^® Gold (Dentsply Sirona, USA), specifically sizes S1 to F3. Final irrigation was performed with 2.5% NaOCl and 17% EDTA, activated by an UltraX ultrasonic irrigation device (Eighteeth, China). The teeth were then randomly assigned to one of three groups for root canal treatment (n = 10): Group I AH Plus^® Bioceramic; Group II Ceraseal^®; Group III AH Plus^®. In Groups I and II, the root canals were moistened using endodontic suction (5 s), followed by paper points (1 s). In Group III, the canals were dried with paper points until the last paper point appeared visibly dry.[15]

Teeth were sectioned horizontally, perpendicular to the root axis, at distances of 4 mm and 8 mm from the apex, with a maximum thickness of 1.5 mm. A micromotor and diamond disk was utilized to obtain the apical and medial segments.

The push-out bond strength testing was conducted using a universal testing machine (Shimadzu AG-5000E). Plunger tip diameters were set at 0.5 mm for the apical segment and 0.8 mm for the medial segment. The maximum load required to break the seal was recorded using computer software, and the push-out bond strength values were expressed in megapascals (MPa).

Following the push-out bond strength test, two observers conducted a failure mode analysis on sixty specimens using a Keyence VH-X 6000 3D digital optical microscope at the magnifications of ×30 and ×100. The results were categorized and presented as percentages across three failure mode groups: Adhesion (no material remaining on the root canal wall), cohesion (material remaining across the entire surface of the root canal wall), and combination (the simultaneous presence and absence of material on the root canal wall).[16]

Statistical analysis

The Kruskal–Wallis test was utilized to assess the differences in push-out bond strength values among the three groups. Subsequently, the Mann–Whitney post hoc test was employed to determine the significance differences between the test groups. For the failure mode analysis, the intraclass correlation coefficient test was conducted to evaluate the consistency of the measurements made by two independent observers. In addition, the Chi-square test was applied to identify the differences in failure modes both within and between the groups. The significance level was at P < 0.05.

RESULTS

In terms of push-out bond strength, Group III demonstrated the highest mean value of 14.65 ± 2.42 MPa, whereas Group I recorded the lowest mean value of 2.31 ± 0.21 MPa. Notably, Group III also achieved the highest maximum value of 38.39 MPa among all the groups. In contrast, Group I exhibited the most limited range of values, spanning from 1.04 to 4.32 MPa [Figure 1].

Figure 1.

Data distribution and significance of push-out bond strength values for AH Plus^® Bioceramic, Ceraseal^®, and AH Plus^®. The use of lowercase letters denotes the significance levels between the various sealer types

The results from the Kruskal–Wallis test indicated a statistically significant difference (P < 0.05) among the three testing groups [Table 1]. When comparing between group variances, Group I showed a statistically significant difference (P < 0.05) when measured against both Group II and Group III. However, no significant difference was found between the Ceraseal^® and AH Plus^® groups [Figure 1].

Table 1.

Push-out bond strength (MPa) of AH plus^® Bioceramic, Ceraseal^® and AH plus^®

Sealer group	n	Median (minimum–maximum)	P
AH plus® Bioceramic	10	2.33 (1.04–4.32)	0.001*
Ceraseal®	10	7.93 (3.16–23.91)
AH plus®	10	11.71 (3.64–38.39)

*Kruskal-Wallis test P<0.05

Failure mode analysis displayed a high level of data reliability (r = 0.907, r > 0.8). The Chi-square test revealed significant differences in failure modes among the three groups (P = 0.019, P < 0.05). Specifically, the AH Plus^® Bioceramic group exhibited notable differences compared to both the Ceraseal^® group (P = 0.018, P < 0.05) and the AH Plus^® group (P = 0.008, P < 0.05). This group was characterized by a significant predominance of mixed failures, which accounted for 85% of the observed failures [Figure 2].

Figure 2.

Distribution of failure modes percentage for AH Plus^® Bioceramic, Ceraseal^®, and AH Plus^® Sealers across three different failure mode categories

In Group II and Group III, however, there was no statistically significant difference in the percentages of cohesive and mixed failures (P = 0.752, P > 0.05). Importantly, no instances of adhesive failure were observed in any of the groups. The presence of cohesive and mixed failures is visually demonstrated in Figure 3, viewed at ×100 magnification.

Figure 3.

Failure mode observation using a digital optical microscope. (a) Cohesive failure (evidenced by residual sealer across the complete dentin surface); (b) Mixed failure (noting sealer residue on a section of the dentin surface). Explanation: Red arrows indicate sealer residue, while blue arrows point to dentin areas devoid of sealer

DISCUSSION

The push-out bond strength test is widely used to evaluate bond strength, although it may not directly predict the success of clinical treatment. Nevertheless, it offers valuable insights for selecting the appropriate sealer, even with the variations in methodology and results.[17] In this study, we employed a consistent procedure, varying only the type of sealer used to minimize variability.

In terms of push-out bond strength, AH Plus^® demonstrated the highest mean value at 14.65 ± 2.42 MPa, while Ceraseal^® showed a comparable mean value. This aligns with the findings of Aly and El Shershaby, who reported similar push-out bond strength values for both Ceraseal^® and AH Plus^®.[18] Previous studies have indicated that AH Plus^® generally offers superior push-out bond strength compared to calcium silicate-based sealers,[19,20,21] a finding confirmed in our study.[4,7] AH Plus^®, an epoxy resin-based sealer, adheres through both mechanical interlocking within dentinal tubules and covalent bonding between resin epoxide groups and amine groups in dentin collagen.[2,3] Its advantages include high bond strength, dimensional stability, and low solubility. However, it lacks bioactive properties and does not form a chemical bond with dentin.[4]

On the other hand, AH Plus^® Bioceramic exhibited the lowest push-out bond strength value, which was significantly different from both AH Plus^® and Ceraseal^®. This finding is consistent with a recent study by Shieh et al., which also reported lower push-out bond strength values for AH Plus^® Bioceramic compared to AH Plus^®.[11] Notably, AH Plus^® Bioceramic contains a lower percentage of calcium silicate (5%–15%) and a higher percentage of zirconium dioxide (50%–70%) compared to previous calcium silicate sealers, which may explain its reduced bond strength.[22] It leads to a lower release of calcium and hydroxyl ions, as well as a reduction in the formation of calcium silicate hydrate. These factors play a crucial role in the mechanical properties and bioactivity of the materials.[23]

Numerous studies have demonstrated that Ceraseal^® and AH Plus^® sealers exhibit favorable setting times and achieve significant penetration into dentinal tubules, contributing to their high performance in push-out tests. Zamparini et al. reported that Ceraseal^® has both faster initial and final setting times compared to AH Plus^® Bioceramic and AH Plus^®.[22] While Ceraseal^® and AH Plus^® showed superior flowability compared to AH Plus^® Bioceramic in the research by Zamparini et al. (2022), Souza et al. (2023) found no significant difference in flowability between AH Plus^® Bioceramic and AH Plus^®.[8] This is plausibly due to AH Plus^® Bioceramic is a newer product that contains 10%–30% dimethyl sulfoxide. It has been explored for its potential as a bonding agent and root canal irrigant, as it may enhance dentin wettability.[24,25]

In addition, Maharti et al. (2023) noted that the particles in Ceraseal^® are smaller, allowing for better penetration into dentin tubules when compared to AH Plus^®. However, the adaptation of both Ceraseal and AH Plus^® to dentin was found to be comparable.[26] In line with it, Mann et al. stated that the penetration depth of Ceraseal^® is deeper which may be due to the particle size, hydrophilicity, and low contact angle.[27] Furthermore, the liquid absorption and solubility properties of AH Plus^® Bioceramic were higher than those of Ceraseal^® and AH Plus^®.[8] Calcium silicate-based sealers such as Ceraseal^® and AH Plus^® Bioceramic utilize bioactivity as their key mechanism. They interact with dentin through the formation of a MIZ, which consists of apatite-like structures.[5,6] Ceraseal^® has shown higher calcium ion release and pH, improving its bioactivity.[22] Its fine particle size and favorable flow properties allow for better dentin penetration.[26,27] However, excessive solubility, a common issue in bioceramics, could reduce bond integrity over time.[8,23]

Increased solubility in calcium silicate-based sealers can enhance the release of ions involved in the biomineralization process. However, excessive solubility may lead to leaching and the formation of voids or porosity in the sealer.[6,22] This excessive porosity can cause lateral deformation and result in cracks or fractures during push-out tests.[23] Several studies have indicated that the solubility of AH Plus^® Bioceramic exceeds the ISO 6876:2012 recommendation of <3% mass loss for sealers.[28]

After conducting the push-out bond strength test, a failure mode analysis was performed to assess the bond between the sealer and dentin. This evaluation utilized a Keyence digital optical microscope (model number: VHX-6000) at magnifications of up to ×100, which allowed for clear visualization of the remaining sealer on the root canal dentin surface.[29] The results indicated that both AH Plus^® and Ceraseal^® displayed a balanced distribution of cohesive and mixed failures, with mixed failures accounting for 45%–50% of the cases. In contrast, AH Plus^® Bioceramic showed a predominance of mixed failures, which accounted for 85% of the observed failures. Previous studies have suggested that AH Plus^® sealers typically exhibit cohesive failure modes, while calcium silicate-based sealers may present either cohesive or mixed failure modes. The predominance of cohesive failures in epoxy resin sealers supports their mechanical strength and uniform adhesion.[13] Previous comparative studies[11,14,18] have corroborated that epoxy resin sealers typically outperform calcium silicate sealers in bond strength tests. The high proportion of mixed failures seen in AH Plus^® Bioceramic could be linked to its lower calcium silicate content, which leads to a reduced formation of calcium silicate hydrate. The mixed failure modes observed in bioceramic sealers may also indicate partial integration with dentin, as well as potential internal weaknesses associated with their high solubility.[8,23] Its bioactive component may not sufficiently contribute to bond development within the 7-day testing period.[30] However, the bioactivity and healing potential of calcium silicates suggest their continued relevance in clinical decision-making.[1,7] The absence of adhesive failures across all groups indicates strong adhesion mechanisms between the calcium silicate sealers and epoxy resin in dentin.[2]

One significant limitation of this study is the moisture content of the dentin in extracted teeth, which is influenced by the medium and duration of storage. Extended storage times may alter the moisture levels in dentin, thereby affecting the collagen matrix and sealer adhesion.[31] Emam et al. found that calcium silicate-based sealer could cause alkaline caustic effect by breaking down the interfacial dentin’s collagenous component.[32] The 7-day observation period for in vitro sealer curing may not adequately represent the full picture of adhesion development, particularly for calcium silicate-based sealers that continue to form apatite bonds over time due to increased pH and calcium release.[8,17,22,33] Singhal et al. reported that the sealing ability of bioceramic sealers with single-cone obturation when exposed to SBF improved significantly after 30 days.[30] Future research could benefit from extending the observation times before testing.

CONCLUSIONS

All sealer groups showed robust adhesion to the dentin surface. However, it is essential to note that the push-out bond strength value of the AH Plus^® Bioceramic sealer was the lowest among the groups.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

This work was supported by PUTI Grant (University of Indonesia) with contract number (NKB-186/UN2.RST/HKP.05.00/2023).