Does the use of different root canal sealers and adhesive resin cements impact the bond strength of glass fiber posts?
Article information
Abstract
Objectives
This study aimed to assess the influence of two endodontic sealers on the bond strength of glass fiber posts using conventional and self-adhesive resin cement through a push-out test.
Methods
Forty central human incisors were randomly divided into four groups (n = 10) based on sealer (epoxy resin-based or calcium silicate-based) and cement (conventional and self-adhesive resin) types: AH Plus (Dentsply DeTrey)/RelyX ARC (3M ESPE), AH Plus/RelyX U200 (3M ESPE), Bio-C Sealer (Angelus)/RelyX ARC, and Bio-C Sealer/RelyX U200. After canal filling and post cementation, roots were sectioned to obtain one specimen per root third. A push-out test and failure pattern assessment were conducted, with bond strength analyzed using the one-way analysis of variance and Tukey test.
Results
AH Plus/RelyX ARC showed the highest bond strength values, with a significant difference in the middle third. The most common failure was mixed (55%), while adhesive failures made up 45%, with 23.5% at the cement/post interface and 21.5% at the cement/dentin interface.
Conclusions
AH Plus/RelyX ARC provided the highest bond strength values for glass fiber posts to dentin.
INTRODUCTION
Restoring teeth that have undergone endodontic treatment presents a distinct challenge, particularly when a significant portion of the coronal structure is compromised or entirely lost. In such scenarios, the prepared root canal space can serve as a foundation for post placement, which aids in retaining restorations like crowns or composite cores, ultimately enhancing the tooth’s structural stability and function [1]. Among the various post options available, glass fiber posts have gained widespread use due to their favorable mechanical and aesthetic characteristics. Their elastic modulus closely resembles that of dentin, facilitating more uniform stress distribution within the tooth structure and consequently minimizing the likelihood of root fractures [2,3].
To minimize adhesive failures—commonly observed in clinical practice as the loss of retention of glass fiber posts—adhesive resin cements are widely recommended. These cements exhibit mechanical properties that harmonize with the composite system formed by the post, cement, and dentin, contributing to a more even stress distribution [4,5]. However, the cementation procedure involves multiple clinical steps, and its complexity may affect the integrity and longevity of the adhesive interface, thereby increasing the likelihood of long-term failure [6,7].
The use of conventional adhesive resin cement involves pretreating the root dentin with phosphoric acid and an adhesive system before applying the cement. In contrast, self-adhesive resin cements simplify this process by eliminating the need for pretreatment. Clinically, they offer advantages such as easier handling, enhanced flow, and reliable bonding to glass fiber posts through a combination of micromechanical interlocking and chemical adhesion [8,9]. Their formulation includes multifunctional hydrophilic monomers with phosphoric acid groups, which interact with hydroxyapatite and penetrate the smear layer [10,11]. This chemical interaction strengthens the bond to dentin [12], reducing the technique’s sensitivity and reliance on operator skill.
Another key factor affecting the bond strength of glass fiber posts cemented with adhesive resin cement is the type and composition of the root canal sealer used to fill the root canal [13–16]. AH Plus (Dentsply DeTrey, Konstanz, Germany), an epoxy resin-based sealer, is widely considered the gold standard due to its superior physicochemical properties [17,18]. Meanwhile, calcium silicate-based sealers have gained popularity in endodontics for their excellent flow, ease of application, and bioactivity—specifically, their ability to form hydroxyapatite during setting [19,20]. Despite this, research on how these sealers influence the adhesion of glass fiber posts to dentin remains limited. The push-out test is a widely used mechanical test designed to evaluate the bond strength between a fiber post and the surrounding root canal dentin. In this test, a controlled force is applied to the post until debonding occurs, simulating the stresses experienced in clinical conditions. By providing a quantitative measure of interfacial adhesion, the push-out test is considered a reliable and reproducible method for assessing the effectiveness of different sealers and cement combinations in post retention.
In this context, the aim of the study was to evaluate the influence of two root canal sealers (AH Plus and Bio-C Sealer [Angelus, Londrina, Brazil]) on the bond strength of glass fiber posts to dentin. The evaluation utilized both conventional and self-adhesive resin cements (RelyX ARC [3M ESPE, Seefeld, Germany] and RelyX U200 [3M ESPE, Seefeld, Germany]), with measurements obtained through a push-out test. The null hypothesis tested was that neither the type of root canal sealer nor the type of resin cement (conventional vs. self-adhesive) would affect the bond strength of glass fiber posts to dentin.
METHODS
Sample size calculation
The determination of sample size was based on a previously published study that followed a comparable methodology [14]. The calculation was performed using an a priori analysis of variance (ANOVA) (fixed effects, omnibus, one-way) from the F-test family in G*Power 3.1.7 software for Windows (Heinrich Heine University Düsseldorf, Düsseldorf, Germany). An effect size of 0.91 was established, with an alpha error of 0.05 and a statistical power of 0.80, leading to a minimum requirement of nine specimens per group. To mitigate the risk of specimen loss, each group included 10 samples.
Specimen selection and grouping
After obtaining approval from the Grande Rio University (protocol no. 5.505.045), 60 extracted human maxillary central incisors, which were removed for reasons unrelated to this study, were initially selected. Patients’ median age was 46 years (range, 24–78 years). Radiographs were taken in both mesiodistal and buccolingual directions to confirm the presence of straight root canals. Teeth presenting resorption, calcifications, root fractures, or prior endodontic treatment were excluded. As a result, 40 specimens met the inclusion criteria and were stored in a 0.1% thymol solution at 5°C until further use.
The crowns of the selected teeth were sectioned 1 mm above the cemento-enamel junction using a low-speed diamond disk, standardizing root lengths to 16 ± 1 mm, as verified with a digital caliper. The specimens were then randomly allocated into four experimental groups (n = 10) according to the combination of root canal sealers (epoxy resin-based or calcium silicate-based) and adhesive cements (conventional and self-adhesive resin) applied: AH Plus/RelyX ARC, AH Plus/RelyX U200, Bio-C Sealer/RelyX ARC, and Bio-C Sealer/RelyX U200 (Table 1).
List of materials with brands, batch number, and chemical composition
Root canal preparation and filling
Following access cavity preparation, apical patency was verified by advancing a size 10 K-file (Dentsply Sirona Endodontics, Konstanz, Switzerland) until its tip extended slightly beyond the apical foramen. The working length (WL) was determined as 1.0 mm short of this point. A glide path was then established using a size 15 K-file (Dentsply Sirona Endodontics) up to the WL. To simulate a closed-end system, the apical third of each root was sealed with hot glue before embedding the specimens in polyvinyl siloxane (Speedex; Coltène, Cuyahoga Falls, OH, USA).
Root canal preparation was carried out using Reciproc Blue R50 instruments (VDW, Munich, Germany) with the VDW Silver motor set to the ‘RECIPROC ALL’ preset program. The instrument was gently advanced apically in a controlled in-and-out pecking motion with a 3-mm amplitude and minimal apical pressure until reaching the WL. After three pecking motions, the instrument was withdrawn and cleaned. Following each removal, 3 mL of 2.5% sodium hypochlorite (NaOCl) was delivered using a NaviTip 30-gauge needle (Ultradent Products Inc., South Jordan, UT, USA), positioned 2 mm short of the WL. Each canal received a total of 12 mL of 2.5% NaOCl for irrigation, followed by a final rinse with 3 mL of 17% EDTA and 5 mL of distilled water. All procedures were performed by a single experienced endodontist.
The root canals were dried using Reciproc Blue R50 absorbent paper points (VDW) and subsequently filled with Reciproc Blue R50 gutta-percha cones (VDW) using the single-cone technique. AH Plus Jet and Bio-C Sealer were employed as sealers according to the assigned groups. In the AH Plus Jet groups, the sealer was mixed using the automix tip and introduced into the canal. For the Bio-C Sealer groups, the sealer was dispensed with the provided needle. A Reciproc Blue R50 gutta-percha cone was then inserted up to the WL. Excess gutta-percha was eliminated with a heat carrier and compacted vertically using a condenser. To assess the quality of the root canal filling, digital radiographs were taken from both buccolingual and mesiodistal perspectives. The access cavities were sealed with light-cure glass ionomer, and all specimens were stored at 37°C with 100% humidity for 1 week.
Glass fiber post cementation procedures
The root canals were re-accessed using diamond burs under continuous water cooling, and part of the root canal filling was removed with size 2 Largo Peeso drills (Dentsply Maillefer Endodontics), leaving 5 mm of gutta-percha in the apical third. Digital radiographs were taken to verify the complete removal of the filling material. The post space was then prepared to a depth of 10 mm using the corresponding bur from the Exacto glass fiber post system (Angelus) to accommodate a size 2 post. After preparation, the canal space was rinsed with 5 mL of distilled water and dried using Reciproc Blue R50 absorbent paper points.
Glass fiber posts were cleaned by immersion in 70% ethyl alcohol for 1 minute and subsequently silanized with RelyX Silane Agent (3M ESPE, St. Paul, MN, USA) using a disposable microbrush, allowing a reaction time of 1 minute. This step was performed immediately before cementation for all posts, regardless of the group.
In the AH Plus/RelyX ARC and Bio-C Sealer/RelyX ARC groups, the root canal walls were treated with 37% phosphoric acid for 15 seconds, followed by rinsing with distilled water for 30 seconds and drying with absorbent paper points. The Adper Scotchbond Multi-Purpose adhesive system (3M ESPE, St. Paul, MN, USA) was applied, with the primer actively brushed for 10 seconds, followed by an air jet for another 10 seconds. The adhesive was then applied to the canal walls for an additional 10 seconds using a microbrush and light cured with the Valo Grand Cordless light-curing unit (Ultradent Products Inc.). RelyX ARC cement was dispensed into the root canal using automix tips, the fiber post was positioned, and light curing was performed for 40 seconds.
For the AH Plus/RelyX U200 and Bio-C Sealer/RelyX U200 groups, RelyX U200 self-adhesive resin cement was mixed and applied directly into the canals using automix tips, without prior dentin treatment. The fiber post was then positioned and light cured for 40 seconds.
All procedures were performed by a single endodontist, and the specimens were stored at 37°C with 100% humidity for 1 week.
Push-out test and failure pattern analysis
The roots were embedded in chemically cured acrylic resin blocks and transversely sectioned using a diamond disc under continuous water cooling with a precision cutting machine (Isomet 1000; Buehler, Lake Forest, IL, USA). Each specimen was sectioned into three slices, measuring 2 ± 0.3 mm in thickness, corresponding to the cervical, middle, and apical thirds of the post space. Each group produced 30 slices, with 10 from each third (n = 10), totaling 120 slices. No specimens were lost during sectioning. To avoid any compromise to the cement interface, push-out tests were performed immediately after sectioning (Figure 1).
Flowchart of slices per experimental group.
Each slice was positioned on a metallic device with a central opening (Ø = 3 mm), ensuring that the canal diameter remained unrestricted. A metallic cylinder with an active tip (Ø tip = 0.8 mm) applied force in an apical-to-coronal direction, preventing pressure on the cement or dentin during testing.
The push-out test was conducted using a universal testing machine (Emic DL-2000; Emic, São José dos Pinhais, Brazil) operating at a speed of 1 mm/min. Bond strength values (σ) in MPa were determined using the equation: σ = F/A, where F is the fracture load (N), and A represents the area of the fiber post (mm²). The post area was calculated with the formula: A = 2 × π × g (R1 + R2), where π = 3.14, g = slant height, R1 = smaller base radius, and R2 = larger base radius. The slant height was determined using the equation: g2 = (h2 + [R2 – R1]2), where h is the section height. R1 and R2 corresponded to the internal diameters of the smaller and larger bases, measured to reflect the space between the root canal walls. A digital caliper was used for all diameter and height measurements. One blinded operator conducted the push-out tests, while another was responsible for the measurements.
Each slice was examined under a stereomicroscope (StereoDiscovery V20; Carl Zeiss, Göttingen, Germany) at 10× magnification by two operators. In cases where discrepancies arose, a third operator provided the final assessment. Failure patterns were categorized as follows: adhesive at the cement/dentin interface, adhesive at the cement/post interface, cohesive in the dentin, cohesive in the cement, cohesive in the post, and mixed. Mixed failures included cohesive failure in the cement combined with adhesive failure at the post-cement interface, cohesive failure in the cement with adhesive failure at the cement-dentin interface, or a combination of adhesive failures at both interfaces with cohesive failure in the cement (Figure 2).
Failures observed in the present study. (A) Adhesive failure at the cement-dentin interface. (B) Mixed failure: adhesive at the post-cement interface, adhesive at the cement-dentin interface, and cohesive in cement. (C) Adhesive failure at the cement-post interface.
Statistical analysis
Data were statistically analyzed using BioEstat ver. 5.0 software (AnalystSoft Inc., Walnut, CA, USA). The Kruskal-Wallis normality test confirmed a normal distribution of the data. Overall, the data followed a Gaussian curve (Shapiro-Wilk test, p < 0.05). Based on this observation, one-way ANOVA and Tukey tests were employed to estimate the impact of independent variables among the groups (AH Plus/RelyX ARC, AH Plus/RelyX U200, Bio-C Sealer/RelyX ARC, and Bio-C Sealer/RelyX U200) on the push-out resistance for the different endodontic sealers and adhesive resin cements in all thirds of the root canal. The significance level was set at 0.05.
RESULTS
Table 2 shows the mean bond strength values for each experimental group, based on the root canal sealer and resin cement used for fiber post cementation. Intergroup analysis indicated that the AH Plus/RelyX ARC combination achieved the highest bond strength values in the middle third (p < 0.05). In the apical third, AH Plus/RelyX ARC showed a statistically significant difference compared to the AH Plus/RelyX U200 and Bio-C Sealer/U200 groups (p < 0.05). Intragroup analysis showed no significant differences between the thirds of the root within any of the four groups (p > 0.05).
Values of bond strength for the experimental groups after the push-out test
Table 3 shows the distribution of failure patterns, with mixed failure being the most common type, occurring in about 55% of specimens. This included adhesive failures at both the cement/post and cement/dentin interfaces, as well as cohesive failures within the cement. Adhesive failures accounted for nearly 45% of the cases, with 23.5% occurring at the cement/post interface and 21.5% at the cement/dentin interface.
Percentage distribution of failure modes across the analyzed groups
DISCUSSION
This study assessed the impact of an epoxy resin-based sealer (AH Plus Jet) and a calcium silicate-based sealer (Bio-C Sealer) on the bond strength of glass fiber posts cemented with either conventional adhesive resin cement (RelyX ARC) or self-adhesive resin cement (RelyX U200) using a push-out test. Notably, the AH Plus/RelyX ARC combination yielded the highest bond strength in the middle third (p < 0.05). In the apical third, this combination exhibited significantly higher bond strength than both the AH Plus/RelyX U200 and Bio-C Sealer/RelyX U200 groups (p < 0.05). These findings led to the rejection of the null hypothesis, underscoring that both the type of sealer and the choice of resin cement significantly impact bond strength outcomes.
As previously noted, the type of root canal sealer can influence the bond between adhesive resin cement and glass fiber posts [13,14]. In this study, the Bio-C Sealer/RelyX ARC group exhibited a nearly 40% reduction in bond strength compared to AH Plus/RelyX ARC. This finding aligns with previous research, which indicated that calcium silicate-based root canal sealers negatively affect the bond strength of glass fiber posts to root dentin [14,21]. Despite efforts to thoroughly remove filling materials before post cementation, residual calcium silicate-based sealer may remain embedded in the dentinal tubules, influencing outcomes even after post space cleaning and preparation [21,22]. Additionally, tag-like structures, consisting of either sealers or hydroxyapatite crystals, may form, suggesting intratubular precipitation [23]. These calcium- and phosphate-rich precipitates, due to the high alkaline pH, can diminish the effectiveness of phosphoric acid etching and impede the formation of a hybrid layer with conventional adhesive resin cement [23]. On the other hand, the superior results observed with the combination of AH Plus root canal sealer and RelyX ARC, a conventional adhesive resin cement, may be attributed to the compatibility between the components of the epoxy resin-based sealer and the adhesive resin cement used for fiber post cementation [24]. This compatibility potentially facilitates stronger adhesion by promoting a more cohesive and durable bond interface between the resin cement and root dentin, further underscoring the importance of sealer choice in enhancing post retention and long-term stability.
Self-adhesive cements provide a convenient alternative for cementing glass fiber posts by simplifying the application process and ensuring strong adhesion to dental structures. They reduce working time by eliminating steps such as acid etching, primer application, and adhesive placement on the dental substrate [12,25]. Despite these advantages, the groups cemented with the self-adhesive RelyX U200 exhibited the lowest bond strength values, regardless of the root canal sealer used. This reduced performance may stem from the acidic resin monomers in RelyX U200, which, though formulated for enamel and dentine etching, may not achieve the same depth of demineralization as phosphoric acid [26,27]. These results are consistent with previous studies showing that conventional adhesive cements typically achieve higher bond strength values than self-adhesive options [26,27].
The study results indicated a predominance of mixed failures (55%) in the push-out tests, whereas adhesive failures constituted 45% of failures, with 23.5% occurring at the cement/post interface and 21.5% at the cement/dentin interface. Notably, the Bio-C Sealer/RelyX U200 combination demonstrated a higher frequency of mixed failures, which may suggest a strong interaction between the calcium silicate-based sealer and the self-adhesive resin cement [13]. In contrast, in the Bio-C Sealer/RelyX ARC group, adhesive failures at the cement/dentin interface were predominant, potentially due to residual filling materials on the dentinal walls, which could reduce bonding efficiency [22]. For the AH Plus/RelyX ARC combination, most failures were adhesive at the cement/post interface, likely reflecting the influence of post surface treatment on cement adhesion. In this study, the glass fiber post was cleaned with alcohol and treated with silane, aiming to enhance bonding at this interface [2]. When AH Plus was used with RelyX U200, mixed failures were more prevalent, suggesting a satisfactory bond between the epoxy-based sealer and the self-adhesive resin cement, underscoring the compatibility of these materials in terms of bonding performance. Importantly, when analyzing failure distribution patterns, it becomes evident that the type of resin cement had a greater influence than the type of endodontic sealer. In both groups where RelyX U200 was used, regardless of whether Bio-C Sealer or AH Plus was applied, mixed failures were predominant. Conversely, in groups where RelyX ARC was used, failure modes varied according to the sealer: adhesive failures at the cement/post interface when combined with AH Plus and at the cement/dentin interface when combined with Bio-C Sealer. This suggests that the adhesive strategy of the resin cement played a more decisive role in determining the failure mode than the endodontic sealer itself. These findings reinforce the importance of selecting an appropriate resin cement to optimize post retention and interfacial adhesion.
While these laboratory tests were conducted in controlled settings, caution is warranted when applying these results directly to clinical practice. Nonetheless, the study offers significant insights by systematically evaluating how different sealer-cement combinations influence bond strength, providing a detailed understanding of material compatibility and its impact on restoration integrity. The inclusion of two commonly used resin cements and root canal sealers further adds clinical relevance, enabling a more comprehensive perspective on adhesive performance across diverse restorative scenarios.
Clinically, these findings underscore the need for practitioners to carefully select sealers and cements based on their compatibility, particularly in cases involving high stress or complex post and core restorations. Future studies should seek to confirm these in vitro results through in vivo trials that assess long-term performance, ideally exploring the specific interactions between calcium silicate-based sealers and adhesive cements under variable conditions, such as temperature changes, and masticatory forces. In addition, the effect of sealers on the dentin microstructure at the microscopic level should also be investigated. Expanding this research could help refine adhesive strategies and optimize the success of restorations involving fiber-reinforced posts, ensuring they meet both functional and aesthetic demands in clinical applications.
CONCLUSIONS
The combination of AH Plus root canal sealer with RelyX ARC cement provided the highest bond strength values to dentin for glass fiber posts. The authors declare no other conflicts of interest.
Notes
CONFLICT OF INTEREST
Emmanuel João Nogueira Leal da Silva is the Associate Editor of Restorative Dentistry and Endodontics and was not involved in the review process of this article.
FUNDING/SUPPORT
This study was partially funded by CAPES (n.001), CNPq and FAPERJ.
AUTHOR CONTRIBUTIONS
Conceptualization, Data curation: Porto ARNP, da Silva EJNL. Formal analysis, Investigation, Methodology: all authors. Funding acquisition, Project administration, Resources, Supervision: da Silva EJNL. Software: Porto ARNP, Belladonna FG, Vieira VTL. Writing - original draft: Porto ARNP, Moreira RF, Vieira VTL. Writing - review & editing: Belladonna FG, da Silva EJNL. All authors read and approved the final manuscript.
DATA SHARING STATEMENT
The datasets are not publicly available but are available from the corresponding author upon reasonable request.