Successful final restoration is important for the long term success of root canal treatment. A lack of adhesion in a final restoration could result in apical or coronal leakage that causes problems in the root canal treatment1,2). Endodontically-treated teeth frequently require extensive restorations with post-core system3,4).

Since composite resin bonds to the structure of teeth, it can reinforce the structure5), and composite resin, along with the dentin bonding agent, was able to restore the access cavity or build the core in endodontically-treated teeth.

When composite resin is used as a restorative material after root canal filling, the residual sealer may come into contact with the resin adhesive, which may influence its adhesive properties. It has been shown that some endodontic materials can interfere with the adhesion of composite resin6-11). A zinc oxide-eugenol (ZOE)-based sealer reduced post retention whereas a resin-based and a calcium hydroxide-based sealers did not affect post retention significantly, as compared to that without a sealer4). An epoxy resin sealer showed no significant differences when comparing the tensile or compressive strength of composite resin restoration12).

More research is needed regarding the influence of a root canal sealer on the bond strength of composite resin restoration. Therefore, the purpose of this study was to evaluate the influence of root canal sealers on the shear bond strength of composite resin on dentin, after the mechanical removal of the sealer13-15).

The results of the shear bond strength test are shown in Figure 2.

The AH-26 group and the control group showed significantly higher shear bond strength than the ZOE group (p < 0.05).

There was no significant difference between the control group and the AH-26 group (p > 0.05).

The results of the present study showed that canal filling materials can affect the bonding of composite resins and the dentin bonding agent to dentin20-23). It is known that resin polymerization can be affected by reducing agents such as phenolic compounds like eugenol24,25). Reducing agents may inhibit the adhesion of the adhesive restoration system based upon a vinylic polymerization mechanism. In the present study, the ZOE sealer treated-dentin showed a less bond strength than the untreated dentin. The results of the present study support this hypothesis.

Although eugenol does not affect on the bond strength of composites on enamel, contradictory finding exist regarding the effect of eugenol on the bond strength on dentin. While some researches9,11,24,25) have found that pre-treatment with eugenol containing-temporary cements decreases bond strength of composites on dentin, other researches have found otherwise5,6,8,10,11).

In contrast to eugenol, epoxy resin does not interact with the free-radical initiation for the composite resin. As a result, no interruption of the setting reaction occured in the present study. AH-26 has epoxy resin polymer chemistry. For epoxy resin, there is an opening of the epoxy monomer ring that results in a final polymer matrix, which contains free (-OH) groups. Since the final epoxy matrix contains a free hydroxyl group, bonding to the free radical, produced in the initiation stage of the setting reaction for the composite resin, is possible. A review of literature12,26), however, indicates that the opening of the epoxy monomer ring takes many hours, even days, whereas a full cure of the composite resin can be achieved in several minutes. Therefore, by incorporating AH-26 into the final polymer matrix of the composite resin, it does not participate chemically in the setting reaction12).

In the present study, the AH-26 treated dentin showed a similar bond strength to the untreated one, and a higher bond strength than the ZOE sealer-treated one.

It was hypothesized that the current dentinbonding systems effectively remove residual cement and eugenol-contaminated dentin and consequently, are insensitive to pre-treatment with eugenol-containing temporary restorations9). In the case of the AH-26 treated group, we can hypothesize that the effects of AH-26 do not seem to be strong enough to alter tensile strength. One may hypothesize the following: that contaminants remain on the dentin surface after cleansing; that they were soluble in the core material; and that they did not interfere with polymerization. A second possible explanation is that most or all of the contaminants on the surface were removed by the etching and bonding procedures. A third plausible explanation could be that the etchant used by the One-step adhesive system dissolved the remaining contaminants, thus eliminating their potential in reducing bond strength27). The clinical significance of this theory, however, it is questionable.

On the other hand, the AH-26 group showed significantly higher values than the ZOE-treated group. The AH-26 group didn't show any significantly different values as compared to the control group.

These results should be kept in mind when selecting appropriate materials regarding composite resin core build up. Insufficient debridement of a eugenol-based material from the dentinal surfaces may affect the quality, retention, and strength of the composite resin core build-up. In order to avoid these problems, it is better to use a material that does not contain eugenol, such as an epoxy resin root canal sealer.

Therefore, in conclusion, our study showed that the epoxy resin sealer AH-26 seemed to have no significant adverse effect on the shear bond strength of composite resin on dentin, while the ZOE sealer did show such effects.

When composite resin restoration is planned after root canal treatment, it may be desirable to use the AH-26 as a root canal sealer from the standpoint of shear bond strength. Further study is necessary to evaluate the effect of the AH-26 on the dentin bonding within a clinical environment.