Adhesion of endodontic sealers to dentin and gutta-percha

Shear bond strength of Resilon to a methacrylate-based root canal sealer

AIM

To evaluate the adhesive strength of Resilon to Next root canal sealant (Heraeus-Kulzer), a methacrylate-based root canal sealer, using a modified microshear bond testing design.

METHODOLOGY

Flat Resilon surfaces of different roughnesses (smooth surface and surface roughness equivalent to 320-grit and 180-grit) were prepared by compression moulding for bonding to the sealer and compared with a composite control. The shear strength data were statistically analysed using Kruskal-Wallis one-way anova on ranks and Dunn's multiple comparison tests (alpha = 0.05). After shear testing, fractured specimens were examined using a field emission-scanning electron microscope for detailed analysis of the failure modes.

RESULTS

The composite control exhibited significantly higher mean shear strength (7.62 MPa) that was 4.4-4.7 times those of the Resilon groups (1.64-1.74 MPa; P < 0.001). Increasing the surface roughness of the Resilon surface did not contribute to further improvement in shear bond strength for this methacrylate-based sealer (P > 0.05). Failure modes in the composite control were cohesive and mixed failures, while those in the Resilon groups were predominantly adhesive failures, with a small percentage of mixed failures. Ultrastructural evidence of phase separation of polymeric components could be identified in Resilon. Both intact, non deformed and plastically deformed Resilon surfaces could be observed in specimens that exhibited adhesive failures.

CONCLUSION

The low shear strength of Resilon to a methacrylate-based sealer compared with a composite control suggests that the amount of dimethacrylate incorporated in this filled, polycaprolactone-based thermoplastic composite may not yet be optimized for effective chemical coupling to methacrylate resins.

Effectiveness of Resin-Coated Gutta-Percha Cones and a Dual-Cured, Hydrophilic Methacrylate Resin-Based Sealer in Obturating Root Canals

The introduction of a polybutadiene-diisocyanate-methacylate resin-coating of gutta-percha enables the polyisoprene to be chemically coupled to methacrylate-based resin root canal sealers. This study examined the effectiveness of using passively fitting cones of this type of gutta-percha with a dual-cured version of EndoREZ sealer in obturating cleaned and shaped root canals. The hydrophilic nature of the sealer enabled the creation of an extensive network of 800 to 1200 mum long sealer resin tags after removal of the endodontic smear layer. Although no adhesive was employed, thin hybrid layers in root dentin were observed when EDTA was used as the final rinse. Nevertheless, interfacial gaps and silver leakage could be observed along the sealer-dentin interfaces that might be attributed predominantly to polymerization shrinkage of the sealer. Gaps and silver leakage were also identified between the gutta-percha resin-coating and the sealer.

The Influence Of Smear Layer On Coronal Leakage Of Roth 801 And AH26 Root Canal Sealers

The aim of this in vitro study was to examine the effect of removal of smear layer on the coronal seal of two commonly used root canal sealers: Roth 801, a zinc oxide-eugenol-based sealer and AH26, an epoxy resin-based sealer. Ninety-six single-rooted human teeth were used. The teeth were instrumented and assigned to four experimental groups of 20 teeth each, with 10 teeth as controls and the remaining six teeth examined under a scanning electron microscope. The teeth in the experimental groups (80 teeth) were divided into four sub-groups and were obturated by laterally condensed gutta-percha with the two sealer cements as follows: Group A1: smear layer left intact and AH26 cement used as sealer; Group A2: smear layer left intact and Roth 801 cement used as sealer; Group B1: smear layer removed and AH26 cement used as sealer; and Group B2: smear layer removed and Roth 801 cement used as sealer. Coronal microleakage was evaluated by measuring the distance of dye penetration. The data was statistically evaluated using a two-way ANOVA test. The results showed that removal of the smear layer resulted in a statistically significant reduction of microleakage values in the groups obturated with AH26 compared with the groups obturated with Roth 801 sealer. It was concluded that the removal of smear layer has a significant influence on the degree of microleakage in obturated root canals.

Ultrastructural Evaluation of the Apical Seal in Roots Filled with a Polycaprolactone-Based Root Canal Filling Material

This in vitro study compared the ultrastructural quality of the apical seal achieved with Resilon/Epiphany and gutta-percha/AH Plus. Single-rooted extracted human teeth were prepared using a crown-down technique, debrided with NaOCl and EDTA, and obturated with either Resilon/Epiphany or gutta-percha/AH Plus. They were examined for gaps along canal walls using SEM, and for apical leakage using a transmission electron microscopy (TEM). SEM revealed both gap-free regions, and gap-containing regions in canals filled with both materials. TEM revealed the presence of silver deposits along the sealer-hybrid layer interface in Resilon/Epiphany, and between the sealer and gutta-percha in the controls. It is concluded that a complete hermetic apical seal cannot be achieved with either root filling materials.

Shear Bond Strength of Three Resin Based Sealers to Dentin With and Without the Smear Layer

Bond strength of root canal sealers to dentin is an important property for the integrity of the sealings of root-canals. The purpose of this study was to test shear bond strength of three endodontic sealers (Diaket, AH Plus and Endo-REZ). The coronal two thirds of ninety extracted human third molars were removed. The smear layer of the exposed dentin surfaces were removed using 17% EDTA followed by 5.25% NaOCl and the teeth were randomly divided into two groups (n = 45). Group 1 was kept as control and in group 2, uniform smear layer was created using waterproof polishing papers. Three-mm long sections of polyethylene tubing were filled with freshly mixed sealer and placed on the dentin surfaces for conducting a shear bond strength test. The data was calculated as MPa and was statistically analyzed using a two way ANOVA, Kruskal-Wallis and Mann-Whitney U tests. A significant difference was found among the bond strength of the sealers, smear layer, and control groups. AH Plus sealer showed the highest bond strength in smear layer removed surfaces (p < 0.05). Pretreatment with EDTA/NaOCl affected bond strength of AH Plus. AH Plus had the highest bond to dentin with or without smear layer.

An In Vitro Comparison of the Sealing Ability of Three Endodontic Sealers Used in Canals with Iatrogenic Enlargement of the Apical Constriction

In cases of disrupted apical constriction effort is made to create an apical stop and subsequently instrument and obturate the canal up to this point. The aim of this study was to in vitro evaluate the sealing ability of three root canal sealers used with the lateral compaction technique in teeth with enlarged constriction. Thirty-six single rooted premolars with straight canals were instrumented up to the apical constriction using a step-back technique. The constriction was enlarged and root canal instrumentation 1.5 mm short of the original working length was performed, to create a new apical stop. Teeth were obturated using lateral compaction technique with either Topseal, Roth 811, or Apexit. Teeth were subjected to area-metric analysis of dye penetration in transverse root sections, up to the most coronal extend of the dye. Sections were studied under the stereomicroscope, digital images were processed and leakage area was estimated. Statistical analysis was performed using Student's t test and Wilcoxon matched-pairs signed-rank test. No gutta-percha was extruded into the space between the apical constriction and the new iatrogenically created constriction. Topseal showed statistical significant less leakage. No significant difference was found between Apexit and Roth 811 (t = 0.99; p = 0.75).

Effect of pH Modified EDTA Solution to the Properties of Dentin

The purpose of this study was to evaluate the influence of smear layer removal with 3% EDTA solution (pH of 9.0) on the dentin in terms of the permeability of root canal disinfectants into the dentin, wetting by endodontic sealer, and adhesive strength of the sealer. Three types of disinfectant (formalin cresol, phenol, and calcium hydroxide) and 4 types of endodontic sealers (included eugenol, non-eugenol, polycarboxylic acid, and resin) were used. The contact angle between endodontic sealer solution and dentin decreased in the 3% EDTA group but increased in the 15% EDTA. The adhesive strength of endodontic sealer to dentin increased in the EDTA groups for all types of sealers. The permeability of root canal disinfectants increased to similar degrees in the 3% and the 15% EDTA groups. In comparing these properties, we propose that the 3% EDTA is more useful for clinical applications.

Comparative Study of Apical Sealing Ability of a New Resin-Based Root Canal Sealer

The purpose of this study was to compare the microleakage of two root canal sealers, Fibrefill (resin-based sealer) and calciobiotic root canal sealer (CRCS; calcium hydroxide-based sealer), with and without the presence of smear layer. The model used for the measurement of microleakage was a fluid transport model. Sixty human extracted teeth were used in this study. The teeth were divided into four groups and treated as follows. In group A, the smear layer was left intact, and canals were obturated with gutta-percha and Fibrefill. In group B, the smear layer was removed, and canals were obturated with gutta-percha and Fibrefill. In group C, the smear layer was left intact, and the canals were obturated with gutta-percha and CRCS. In group D, the smear layer was removed, and canals were obturated with gutta-percha and CRCS. Microleakage was measured at 7 days, 1 month, and 2 months. The results showed that the Fibrefill groups with and without smear layer leaked significantly less than the CRCS groups at all experimental times. No significant difference was found between the groups of same materials, but the microleakage values were less when the smear layer was removed.

Adhesion of a New Methacrylate Resin-Based Sealer to Human Dentin

The purpose of this study was to compare the shear bond strength of four root canal sealers: Fibrefill (a methacrylate resin sealer), Endion (a glass ionomer sealer), Topseal (an epoxy resin sealer), and CRCS (a calcium hydroxide sealer) to human root canal dentin. The dentin specimens were divided into four groups of 12 specimens each and etched with 3 ml of EDTA 17% before rinsing with NaOCl 2.5% and distilled water. Bond strength was tested using a test machine by subjecting samples to a shear load at a cross-head speed of 0.5 mm/min. The best results were observed in the Fibrefill group, in which the mean shear bond strength was 7.993 +/- 2.365 MPa. The values in the Endion (1.816 +/- 0.614 MPa) and CRCS (2.224 +/- 0.509 MPa) groups were significantly lower than in the Fibrefill and Topseal (6.235 +/- 1.428 MPa) groups. Inspection of the fractured surfaces revealed the bond failure to be mainly adhesive to dentin for Fibrefill and cohesive for Endion sealer. CRCS and Topseal sealers showed both adhesive and cohesive failures.

Interaction Between Sealers and Gutta-percha Cones

Clinical observations seem to indicate that some gutta-percha cones are softened by contact with sealers. The purpose of the study was to verify whether an interaction existed between some sealers and different brands of gutta-percha cones. Because previous studies have indicated that the differences between brands of gutta-percha are magnified by heat, thermatic compaction was used in conjunction with a model of a root-canal preparation with lateral canals. Three brands of cones (Kerr, UDM, Beldent) were tested with three types of endodontic sealers (AH 26, Apexit, Roth's). A group without sealer served as a control. The length of flow into the lateral canals was measured for each combination and analyzed by two-way ANOVA. A highly significant difference was found, confirming the hypothesis that an interaction between sealer and cones is present in some combinations. It was not possible to ascribe a trend of greater effect to a certain sealer, but Roth's 811 had the least effect on flow.

Cytotoxicity Testing of Endodontic Sealers: A New Method

The purpose of this study was to compare ISO standards versus a new technique for in vitro evaluation of cytotoxicity of root canal sealers. The cytotoxicity of AH Plus, Cortisomol, and Sealapex was first recorded according to ISO standards on L 929 fibroblasts by the MTT assay. In parallel, 30 single-rooted teeth were cut at the cementum enamel junction (CEJ), and the roots were prepared and sterilized before filling with the lateral condensation using one of three sealers (n = 10). The apexes of the roots were dipped into 1 ml of minimum essential medium for 1, 2, and 30 days renewing the medium every other day. After 24-h contact between the medium and the filled roots, the medium was used to measure the cytotoxicity on L 929 with the MTT assay. ISO standards always gave a statistically higher cytotoxicity than the root-dipping technique (p < 0.0001), whatever the sealer and the exposure time. The ISO standards showed statistically significant differences among the sealers (p < 0.0001). AH Plus was noncytotoxic, Cortisomol showed a high cytotoxicity decreasing over time (p < 0.001), and Sealapex displayed a high cytotoxicity that did not decrease over time (NS). The new technique showed statistically significant differences among the sealers (p = 0.001), but the differences were so small that they were likely not clinically relevant. The high cytotoxicity of Sealapex decreased over time but the cytotoxicity of AH Plus and Cortisomol did not. The results show that the ISO standards may strongly over-evaluate the cytotoxicity of the endodontic sealers, emphasize the difference among the sealers, and may clinically correspond to a large overfilling. The new technique reduces the discrimination of the test and may clinically correspond to a classical filling. Therefore, both methods might be considered as clinically relevant, corresponding to classical and overfilling conditions.

Shear bond strength of AH-26 root canal sealer to dentine using three dentine bonding agents

OBJECTIVE

The purpose of the study was to compare the bond strength of AH-26 root canal sealer to human root canal dentine exposed to different intracanal medications both with and without the use of three bonding agents. The materials used were AH-26 sealer, two one-bottle bonding agents (Single Bond, Bond-1) and one self-etching bonding agent (Clearfill SE Bond).

METHODS

The dentine substrate was obtained from single rooted human teeth. The dentine specimens were treated either with EDTA 15% or phosphoric acid 37% to achieve the removal of smear layer. The AH-26 sealer was placed on the dentine surfaces both with and without the use of the bonding agents. Bond strength was tested using a single plane shear test assembly.

RESULTS

The SBS values were (MPa): Group A (EDTA-AH-26) 3.678+/-0.853, Group B (Phosphoric acid-AH-26) 3.470+/-0.834, Group C (EDTA-Single Bond-AH-26) 4.8+/-0.865, Group D (Phosphoric acid-Single Bond-AH-26) 5.043+/-1.022, Group E (EDTA-Bond 1-AH-26) 4.939+/-0.877, Group F (Phosphoric acid-Bond 1-AH-26) 5.101+/-1.117, Group G (Clearfill SE Bond-AH-26) 6.975+/-1.694. The use of dentine bonding agents improved significantly (p<0.05) the adhesion of AH-26 sealer with the root canal dentine. However, the best results were obtained with the self-etching system. Similar results were observed from the pretreatment of dentine either with phosphoric acid 35% or EDTA 15%.

CONCLUSIONS

The use of dentine bonding agents gave higher shear bond strengths of AH-26 sealer to human root canal dentine.