Efficacy of different irrigation regimes on the push-out bond strength of various resin-based sealers at different root levels: An in vitro study.

AIM: This study aims to evaluate and compare the efficacy of various irrigation regimens on push-out bond strength of AH Plus/gutta-percha, Real Seal/Resilon, and MetaSeal/gutta-percha at three different root levels.
MATERIALS AND METHODS: Single-rooted mandibular premolars (n = 120) were prepared and divided into four groups (n = 30) based on irrigation regimen used: I: 5.25% sodium hypochlorite (NaOCl)-17% ethylenediaminetetraacetic acid (EDTA); II: 5.25% NaOCl-2.25% Peracetic acid (PAA); III: 5.25% NaOCl-18% 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) (Etidronic Acid); and IV: Distilled Water. Each group was further divided into three subgroups (n = 10); A: AH Plus/gutta-percha; B: MetaSEAL/gutta-percha; C: RealSeal/Resilon. After obturation, roots were sectioned at 3 levels and push-out tests were performed. One-way ANOVA with post hoc Tukey-honestly significant difference tests were applied to assess the significance among various groups.
RESULTS: Among irrigants, 2.25% PAA showed significantly lower values when compared with rest of the irrigants. There was no significant difference found among EDTA and HEBP. The push-out bond strength of AH Plus was significantly higher among all sealers. The bond strength values were significantly decreased in apico-coronal direction.
CONCLUSIONS: There was superior efficacy of EDTA and HEBP on the bond strength of AH Plus at apical root level when compared with other irrigants and sealers at various root levels.

INTRODUCTION

Successful root canal treatment is dependent on the meticulous cleaning of the root canal system, the eradication of pathogenic organisms and a three-dimensional filling of canal space with an inert root filling material to prevent the ingress of microorganisms from the oral cavity and its spread to the periapical tissue.

During the biomechanical preparation, an iatrogenic layer is formed on the dentinal walls, which are primarily made up of inorganic particles of calcified tissue and some organic materials, including bacteria, necrotic tissue, viable pulp tissue, odontoblastic processes, and blood cells. Therefore, after research, it is advised to remove it for the better clinical results.[1] Till date, no single irrigant has shown both the tissue dissolving and demineralizing property.

Sodium hypochlorite (NaOCl) is one of the prime endodontic irrigating solutions, well known for its tissue dissolving properties. However, its inability to dissolve inorganic contents promotes the use of an additional chemical agent with such properties. Goldman et al. reported that the most efficient method to remove the smear layer is using NaOCl and ethylenediaminetetraacetic acid (EDTA).[2]

As for the second option, Peracetic acid (PAA) is used as a final irrigant. It is a sporicidal, virucidal, bactericidal, and fungicidal in nature, even at low concentrations of < 0.5%. PAA also has an effect on smear layer and root canal wall that is comparable to 17% EDTA.

A soft chelating agent, Etidronic acid, also known as 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP), or Etidronate, has been recently suggested as an alternative to citric acid or EDTA because of its excellent chelating ability.[34]

Endodontic literature has investigated the effect of endodontic irrigants on the bond strength of various types of root canal sealers.[56] Epoxy resin-based sealers such as AH Plus sealer have been used most widely because of its acceptable physical properties, adequate biological performance, apical sealability, reduced solubility, and microretention to root dentin. In addition, it showed a better wettability of dentine and gutta-percha and good handling characteristics.

Recently, the manufacturers have blended the adhesive dentistry and endodontics, thereby introducing an obturation system with a specific concern on achieving a “monoblock” in which the sealer, core material, and the dentin form a single cohesive unit.[7] Resilon-RealSeal system consists of a self-etching primer, sealer and polycaprolactone core material, which resists shrinkage and strengthens the root.

Another sealer has been introduced with claims that it bonds with both Resilon and Gutta-percha as well as dentin. MetaSEAL is a new dual-cure and self-etching resin cement, containing methacryloyloxyethyl trimellitate anhydride (4-META).

No study till date has been done to compare the push-out bond strength of AH Plus/gutta-percha, RealSeal/Resilon, and MetaSeal/gutta-percha when used after various irrigation regimens.

Therefore, the purpose of the study is to assess and compare the efficacy of various irrigation regimens on the push-out bond strength of AH Plus/gutta-percha, RealSeal/Resilon, and MetaSeal/gutta-percha at three different root levels.

The first null hypothesis tested was there is no difference in the efficacy of different irrigants on the push-out bond strength of various sealers at different root levels. The second null hypothesis tested was there is no difference in the push-out bond strength of various sealers. The third null hypothesis tested was there is no difference in the push-out bond strength measured at three different root levels.

MATERIALS AND METHODS

One hundred and twenty single-rooted mandibular premolar teeth completely formed apices, extracted for orthodontic reasons were used in the study. Teeth exhibiting only one canal which was confirmed by X-rays, no cracks or fracture after inspection under an operating microscope (×10), no dilaceration and calcification were included and immediately stored in a 0.9% thymol solution until use.

The teeth were decoronated at cementoenamel junction with a low-speed handpiece (NSK, Kanuma, Japan) and diamond disc under water cooling to obtain a standardized length of 15 mm. Working lengths was established by subtracting 1 mm from the root canal length. This was followed by standardized biomechanical preparation of the canals using Mtwo rotary files (VDW, Munich, Germany) till # 35/0.04 taper. The specimens were randomly divided into four groups of 30 samples each according to irrigation regimen used. Group I: 5.25% NaOCl followed by 17% EDTA; Group II: 5.25% NaOCl followed by 2.25% PAA; Group III: 5.25% NaOCl followed by 18% Etidronic Acid/HEBP; and Group IV: Distilled water (Control). During instrumentation, 1 ml of 5.25% NaOCl was used at each change of file. All the irrigation procedures were performed by EndoVac (Discus Dental, Culver City, CA) as per manufacturer's instructions.

Depending on the type of sealers used for the obturation; each group was further subdivided into 3 subgroups of 10 specimens each, i.e., subgroup A-AH Plus (DENTSPLY Malliefer, Switzerland)/gutta-percha (DENTSPLY Malliefer, Switzerland); subgroup B-MetaSEAL (Sun Medical, Tokyo, Japan, Parkell Inc., Farmingda)/gutta-percha; and subgroup C-RealSeal (SybronEndo, Orange, CA, USA)/Resilon (SybronEndo, Orange, CA, USA) system. In each group obturation was done using lateral compaction technique. The obturated specimens were stored at 37°C and 100% humidity for 1 week to allow setting of the sealers.

Each root was transversally sectioned into three slices of 2 mm thickness each, i.e., coronal, middle and apical. Three different plungers of 1 mm, 0.8 mm, and 0.3 mm diameter were used for coronal, middle, and apical sections, respectively. The test was done using the universal testing machine at a cross-head speed of 2 mm/min.

Push-out strength (MPa) = maximum load (N)/bonding surface area.

The adhered area of each test specimen was calculated using the formula for the conical frustum, i.e.,

Area = π(R1 + R2)√(R1 − R2)2 + H2, where,

H = height of slice.

R1 = internal radius of the greatest base.

R2 = internal radius of the smallest base.

One-way analysis of variance with post hoc analysis (Tukey honestly significant difference) was applied to assess the significance among the various groups using Statistical Package for Social Sciences software, 16.0 Version (SPSS, Chicago, illinois, U.S.A) The statistical significance level was set at P < 0.05.

RESULTS

The mean and standard deviation values of push-out bond strength (MPa) for all the irrigants and sealers at three root levels are listed in Table 1.

Table 1

Comparison of mean push-out bond strength values of different groups in respect to various subgroups at different root levels

The push-out bond strength values of 17% EDTA were the highest among all the irrigants with a nonsignificant difference with 18% HEBP. Whereas 2.25% PAA showed significantly the lowest bond strength values than 17% EDTA and 18% HEBP.

Statistical ranking for bond strength among various sealers obtained was as follows: AH Plus > MetaSEAL > RealSeal, with significant differences among all.

Push-out strength was the highest at apical and the lowest at middle third. However, the differences between the mean values at coronal and middle thirds were not significant.

DISCUSSION

The null hypothesis was rejected as there was difference in the push-out bond strength of AH Plus, MetaSEAL and RealSeal root canal sealers when used with17% EDTA, 2.25% PAA, and 18% HEBP at three different root levels.

In the present study, EndoVac Irrigation System was used and the total contact period of each irrigant during each microcycle was 2 min. This was in accordance with previously reported studies.[89] The rate of flow for each irrigant was standardized to 1 ml/30 s of time period.[10]

In our study, final rinse with distilled water was performed, as it was observed that the use of NaOCl as a final rinse resulted in reduced resin bond strength because it oxidizes the dentinal matrix that inhibits the polymerization process of resins.[11]

Among the irrigants, 17% EDTA demonstrated the highest push-out bond strength values followed by 18% HEBP and 2.25% PAA, with all the sealers at all the root levels. However, the difference between EDTA and HEBP was not statistically significant, whereas other irrigants showed significant differences at all root levels. This could be attributed to the fact that 17% EDTA effectively removed the smear layer that allowed the penetration of the resin into the open dentinal tubules, hence, creating an efficient micro-retention.[1213]

Hashem et al.[5] and Neelakantan et al.[9] found out that the surface treatment with 17% EDTA favors the adhesion of resinous AH Plus.

Since 18% Etidronic acid is a soft chelating agent and produces less depth of demineralized dentin, it facilitates the complete infiltration of resins through exposed collagen fibers.[9] Therefore, this reason might have possibly resulted in comparable bond-strength values between EDTA and HEBP in our study. In accordance to the current findings, Kandaswamy et al.[14] found nonsignificant differences between 18% HEBP and 17% EDTA when used with AH Plus sealer.

Among irrigants, 2.25% PAA showed inferior push-out bond strength values because of its highly acidic pH (pH = 2.5), which resulted in more calcium elution from the root canal dentine. Taneja et al.[15] reported that irrigation with 2.25% PAA caused the highest calcium loss from the root dentin that resulted in reduced microhardness when compared with 17% EDTA.

The lowest push-out bond strength values were evident in control group (Distilled water), in which the smear layer was kept intact indicating the negative effects of undisturbed smear layer on push-out bond strength values.

Among the three sealers, the highest push-out bond strength values were shown by AH Plus followed by MetaSEAL and the least was found in RealSeal with all the irrigants at all root thirds, and the differences between all three of them were statistically significant. The possible reason for the higher values of AH Plus could be attributed to its inherent volumetric expansion property that resulted in the formation of a covalent bond between sealer and exposed amino groups of root dentin by an open epoxide ring that showed photopolymerization.[1617] In a study Rahimi et al.[18] found out that epoxy resin-based sealers showed higher bond strength values when compared to dimethacrylate-based sealers.

MetaSEAL presented inferior bond strength values when compared with AH Plus. Theoretically, methacrylate resin-based sealer forms hybrid layers to dentin and gutta-percha. However, this hybrid layer was either thin or incomplete or nonexistent when observed in self-adhesive MetaSEAL sealer.[19] This might have resulted in the gap formation and subsequent bond failure.

Similar findings were observed by Lawson et al.[20] On the other hand, Belli et al.[19] found no significant differences in the sealing ability of MetaSEAL when compared with AH Plus and RealSeal.

RealSeal showed the lowest value due to the lack of free radicals within the polymerized complex of Resilon.[16] In addition, the large plate-like filler particles of RealSeal align in parallel manner to each other as well as to the dentin, which may hinder the penetration of the sealer within the dentinal tubules.[17]

In the present study, apical third showed significantly higher push-out bond strength value followed by cervical and middle. Although the tubule density decreases from coronal to apical region, the circular cross-section of root canal at apical third might had provided higher resistance to dislodgment forces during the testing. On the other hand, coronal and middle portion has oval or even flattened root canal sections. These variations in the root canal anatomy might lead to misfit of the main gutta-percha and lead to impaired bond strength.[21]

Baldissera et al.[21] compared the effects of different irrigants on sealer-dentin bond strength when using RealSeal and stated that higher bond strength was observed in apical portion in comparison to coronal and middle regions. Contrary to this, clinical trials by clinical trials by Paque et al. (2006),[22] Lottanti et al.[23] reported the highest bond strength in the coronal region in comparison to apical region. The possible explanation for such contrasting findings might be because of the use of positive pressure irrigation technique in their studies.

CONCLUSION

Therefore, our study clearly demonstrates the superior efficacy of EDTA and HEBP on the bond strength of AH Plus at apical root level when compared with other irrigants and sealers at various root levels. Further long-term clinical studies using the similar irrigation protocol and sealers are warranted to substantiate these findings.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.